RE: [PATCH v4 4/5] cxl: CXL Performance Monitoring Unit driver

[Dan Williams]

Jonathan Cameron wrote:
> CXL rev 3.0 introduces a standard performance monitoring hardware
> block to CXL. Instances are discovered using CXL Register Locator DVSEC
> entries. Each CXL component may have multiple PMUs.
> 
> This initial driver supports on a subset of types of counter.

s/on//?

> It support counters that are either fixed or configurable, but requires

s/support/supports/

> that they support the ability to freeze and write value whilst frozen.
> 
> Development done with QEMU model which will be posted shortly.

Per the comment on the cover letter is there a sense that set of
counters supported in QEMU and this patchset are representative of a
"common" set even if that is by convention and not specification? Just
trying to get a sense of how many real world CXL PMU instances this
might cover.

> Reviewed-by: Dave Jiang <dave.jiang@xxxxxxxxx>
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>

One thing I would have liked to see is a sample perf command line and
output.

One concern I have is how usable DPA based perf events is going to be
for end users. Is there a concept of a synthetic event that can turn
data gathered from all the devices in an interleave set into HPA
relative data? Or do you expect that is the responsibility of the perf
tool to grow that support in userspace?

> 
> ---
> v4:
> - Add defines for masks used for config, config1 etc and reorder
>   code so those can be next to the attrs.  Note that one of the
>   bits was wrong showing the advantage of bring all this info
>   into one place.
> - Use enabled counter bitmap rather than pointer array to make the
>   fixed counter handling look more like the variable counter handling.
> - Drop PERF_EF_RELOAD handling that did nothing.
> - Simplify code as nothing special to do if the counting is already
>   up to date (no harm in setting the already set flag).
> ---
>  drivers/cxl/Kconfig  |  13 +
>  drivers/cxl/Makefile |   1 +
>  drivers/cxl/cpmu.c   | 940 +++++++++++++++++++++++++++++++++++++++++++

Yeah, this is a bunch of code and ABI that is more relevant to drivers/perf/
than drivers/cxl/, so this wants to move to drivers/perf/cxl.c.

> diff --git a/drivers/cxl/Kconfig b/drivers/cxl/Kconfig
> index ff4e78117b31..0be514b00b8f 100644
> --- a/drivers/cxl/Kconfig
> +++ b/drivers/cxl/Kconfig
> @@ -139,4 +139,17 @@ config CXL_REGION_INVALIDATION_TEST
>  	  If unsure, or if this kernel is meant for production environments,
>  	  say N.
>  
> +config CXL_CPMU
> +	tristate "CXL Performance Monitoring Unit"
> +	default CXL_BUS
> +	depends on PERF_EVENTS
> +	help
> +	  Support performance monitoring as defined in CXL rev 3.0
> +	  section 13.2: Performance Monitoring. CXL components may have
> +	  one or more CXL Performance Monitoring Units (CPMUs).
> +
> +	  Say 'y/m' to enable a driver that will attach to performance
> +	  monitoring units and provide standard perf based interfaces.
> +
> +	  If unsure say 'm'.
>  endif

...and this wants to move to drivers/perf/Kconfig as well.

It's similar to "CONFIG_DEV_DAX_CXL" as an external to drivers/cxl/
cxl-driver.

> diff --git a/drivers/cxl/Makefile b/drivers/cxl/Makefile
> index db321f48ba52..024bb739554b 100644
> --- a/drivers/cxl/Makefile
> +++ b/drivers/cxl/Makefile
> @@ -5,6 +5,7 @@ obj-$(CONFIG_CXL_MEM) += cxl_mem.o
>  obj-$(CONFIG_CXL_ACPI) += cxl_acpi.o
>  obj-$(CONFIG_CXL_PMEM) += cxl_pmem.o
>  obj-$(CONFIG_CXL_PORT) += cxl_port.o
> +obj-$(CONFIG_CXL_CPMU) += cpmu.o
>  
>  cxl_mem-y := mem.o
>  cxl_pci-y := pci.o
> diff --git a/drivers/cxl/cpmu.c b/drivers/cxl/cpmu.c
> new file mode 100644
> index 000000000000..e6821771a4f6
> --- /dev/null
> +++ b/drivers/cxl/cpmu.c
> @@ -0,0 +1,940 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +
> +/*
> + * Copyright(c) 2023 Huawei
> + *
> + * The CXL 3.0 specification includes a standard Performance Monitoring Unit,
> + * called the CXL PMU, or CPMU. In order to allow a high degree of
> + * implementation flexibility the specification provides a wide range of
> + * options all of which are self describing.
> + *
> + * Details in CXL rev 3.0 section 8.2.7 CPMU Register Interface
> + *
> + * TODO
> + * o Discoverability of counters. Allow perftool to provide summed counters
> + *   and vendor defined counters.
> + * o Support free running counters - copy the Intel uncore PMU handling for these.
> + * o CPMUs which do not support freeze.

Wouldn't this be driven by the arrival of hardware? I.e. is there 
> + * o Add filter validation in cpmu_event_init() so problems are detected earlier.
> + * o Reject configurations that the hardware is ignoring
> + *   (e.g. invert when not invertible)
> + * o Support CPMUs with no interrupts using an HRTIMER.

Is it worthwhile to maintain the TODO list in the code? I just fear this
getting stale over time.

> + */
> +
> +#include <linux/io-64-nonatomic-lo-hi.h>
> +#include <linux/perf_event.h>
> +#include <linux/bitops.h>
> +#include <linux/device.h>
> +#include <linux/bits.h>
> +#include <linux/list.h>
> +#include <linux/bug.h>
> +#include <linux/pci.h>
> +
> +#include "cpmu.h"
> +#include "cxlpci.h"
> +#include "cxl.h"
> +
> +/* CXL rev 3.0 Table 13-5 Events under CXL Vendor ID */
> +#define CPMU_GID_CLOCK_TICKS		0x00
> +#define CPMU_GID_D2H_REQ		0x0010
> +#define CPMU_GID_D2H_RSP		0x0011
> +#define CPMU_GID_H2D_REQ		0x0012
> +#define CPMU_GID_H2D_RSP		0x0013
> +#define CPMU_GID_CACHE_DATA		0x0014
> +#define CPMU_GID_M2S_REQ		0x0020
> +#define CPMU_GID_M2S_RWD		0x0021
> +#define CPMU_GID_M2S_BIRSP		0x0022
> +#define CPMU_GID_S2M_BISNP		0x0023
> +#define CPMU_GID_S2M_NDR		0x0024
> +#define CPMU_GID_S2M_DRS		0x0025
> +#define CPMU_GID_DDR			0x8000

Last note about the naming quibble, I notice that CPMU exists in other
places in the kernel, but CXL_PMU does not, so there is a small
grep'ability win as well.

> +
> +static int cpmu_cpuhp_state_num;
> +
> +struct cpmu_event {
> +	u16 vid;
> +	u16 gid;
> +	u32 msk;
> +	union {
> +		int counter_idx; /* fixed counters */
> +		int event_idx; /* configurable counters */
> +	};
> +	struct list_head node;
> +};
> +
> +#define CPMU_MAX_COUNTERS 64
> +struct cpmu_info {
> +	struct pmu pmu;
> +	void __iomem *base;
> +	struct perf_event **hw_events;
> +	struct list_head events_configurable;
> +	struct list_head events_fixed;

Linked lists? Didn't xarray kill the linked list?

> +	DECLARE_BITMAP(used_counter_bm, CPMU_MAX_COUNTERS);
> +	DECLARE_BITMAP(conf_counter_bm, CPMU_MAX_COUNTERS);
> +	u16 counter_width;
> +	u8 num_counters;
> +	u8 num_event_capabilities;
> +	int on_cpu;
> +	struct hlist_node node;
> +	bool freeze_for_enable;
> +	bool filter_hdm;
> +	int irq;
> +};
> +
> +#define pmu_to_cpmu_info(_pmu) container_of(_pmu, struct cpmu_info, pmu)
> +
> +/*
> + * All CPMU counters are discoverable via the Event Capabilities Registers.
> + * Each Event Capability register contains a a VID / GroupID.
> + * A counter may then count any combination (by summing) of events in
> + * that group which are in the Supported Events Bitmask.
> + * However, there are some complexities to the scheme.
> + *  - Fixed function counters refer to an Event Capabilities register.
> + *    That event capability register is not then used for Configurable
> + *    counters.
> + */
> +static int cpmu_parse_caps(struct device *dev, struct cpmu_info *info)
> +{
> +	DECLARE_BITMAP(fixed_counter_event_cap_bm, 32) = {0};

An 'unsigned long' is always at least 32-bits, and:

unsigned long fixed_counter_event_cap_bm = 0;

...would not have interrupted my reading of the code.

> +	void __iomem *base = info->base;
> +	u64 val, eval;
> +	int i;
> +
> +	val = readq(base + CPMU_CAP_REG);
> +	info->freeze_for_enable = FIELD_GET(CPMU_CAP_WRITEABLE_WHEN_FROZEN, val) &
> +		FIELD_GET(CPMU_CAP_FREEZE, val);

Why does 'struct cpmu_info' need to carry the freeze_for_enable flag if
its only used to gate loading the driver?

When / if support for "freeze_for_enable == false" arrives then I can
see 'struct cpmu_info' having a need to cache it.

> +	if (!info->freeze_for_enable) {
> +		dev_err(dev, "Driver does not support CPMUs that do not support freeze for enable\n");

Perhaps just:

"Counters not writable while frozen."

...will suffice, no need to mention what the driver supports, that's
implied.

> +		return -ENODEV;
> +	}
> +
> +	info->num_counters = FIELD_GET(CPMU_CAP_NUM_COUNTERS_MSK, val) + 1;
> +	info->counter_width = FIELD_GET(CPMU_CAP_COUNTER_WIDTH_MSK, val);
> +	info->num_event_capabilities = FIELD_GET(CPMU_CAP_NUM_EVN_CAP_REG_SUP_MSK, val) + 1;
> +
> +	info->filter_hdm = FIELD_GET(CPMU_CAP_FILTERS_SUP_MSK, val) & CPMU_FILTER_HDM;
> +	if (FIELD_GET(CPMU_CAP_INT, val))
> +		info->irq = FIELD_GET(CPMU_CAP_MSI_N_MSK, val);
> +	else
> +		info->irq = -1;
> +
> +	/* First handle fixed function counters; note if configurable counters found */
> +	for (i = 0; i < info->num_counters; i++) {
> +		struct cpmu_event *cpmu_ev;
> +		u32 events_msk;
> +		u8 group_idx;
> +
> +		val = readq(base + CPMU_COUNTER_CFG_REG(i));
> +
> +		if (FIELD_GET(CPMU_COUNTER_CFG_TYPE_MSK, val) ==
> +			CPMU_COUNTER_CFG_TYPE_CONFIGURABLE) {
> +			set_bit(i, info->conf_counter_bm);
> +		}
> +
> +		if (FIELD_GET(CPMU_COUNTER_CFG_TYPE_MSK, val) !=
> +		    CPMU_COUNTER_CFG_TYPE_FIXED_FUN)
> +			continue;
> +
> +		/* In this case we know which fields are const */
> +		group_idx = FIELD_GET(CPMU_COUNTER_CFG_EVENT_GRP_ID_IDX_MSK, val);
> +		events_msk = FIELD_GET(CPMU_COUNTER_CFG_EVENTS_MSK, val);
> +		eval = readq(base + CPMU_EVENT_CAP_REG(group_idx));
> +		cpmu_ev = devm_kzalloc(dev, sizeof(*cpmu_ev), GFP_KERNEL);
> +		if (!cpmu_ev)
> +			return -ENOMEM;
> +
> +		cpmu_ev->vid = FIELD_GET(CPMU_EVENT_CAP_VENDOR_ID_MSK, eval);
> +		cpmu_ev->gid = FIELD_GET(CPMU_EVENT_CAP_GROUP_ID_MSK, eval);
> +		/* For a fixed purpose counter use the events mask from the counter CFG */
> +		cpmu_ev->msk = events_msk;
> +		cpmu_ev->counter_idx = i;
> +		/* This list add is never unwound as all entries deleted on remove */
> +		list_add(&cpmu_ev->node, &info->events_fixed);
> +		/*
> +		 * Configurable counters must not use an Event Capability registers that
> +		 * is in use for a Fixed counter
> +		 */
> +		set_bit(group_idx, fixed_counter_event_cap_bm);
> +	}
> +
> +	if (!bitmap_empty(info->conf_counter_bm, CPMU_MAX_COUNTERS)) {
> +		struct cpmu_event *cpmu_ev;
> +		int j;
> +		/* Walk event capabilities unused by fixed counters */
> +		for_each_clear_bit(j, fixed_counter_event_cap_bm,
> +				   info->num_event_capabilities) {
> +			cpmu_ev = devm_kzalloc(dev, sizeof(*cpmu_ev), GFP_KERNEL);
> +			if (!cpmu_ev)
> +				return -ENOMEM;
> +
> +			eval = readq(base + CPMU_EVENT_CAP_REG(j));
> +			cpmu_ev->vid = FIELD_GET(CPMU_EVENT_CAP_VENDOR_ID_MSK, eval);
> +			cpmu_ev->gid = FIELD_GET(CPMU_EVENT_CAP_GROUP_ID_MSK, eval);
> +			cpmu_ev->msk = FIELD_GET(CPMU_EVENT_CAP_SUPPORTED_EVENTS_MSK, eval);
> +			cpmu_ev->event_idx = j;
> +			list_add(&cpmu_ev->node, &info->events_configurable);
> +		}
> +	}
> +
> +	return 0;
> +}
> +
> +static ssize_t cpmu_format_sysfs_show(struct device *dev,
> +				      struct device_attribute *attr, char *buf)
> +{
> +	struct dev_ext_attribute *eattr;
> +
> +	eattr = container_of(attr, struct dev_ext_attribute, attr);
> +
> +	return sysfs_emit(buf, "%s\n", (char *)eattr->var);
> +}
> +
> +#define CPMU_FORMAT_ATTR(_name, _format)\
> +	(&((struct dev_ext_attribute[]) {				\
> +		{							\
> +			.attr = __ATTR(_name, 0444,			\
> +				       cpmu_format_sysfs_show, NULL),	\
> +			.var = (void *)_format				\
> +		}							  \
> +		})[0].attr.attr)
> +
> +enum {
> +	cpmu_mask_attr,
> +	cpmu_gid_attr,
> +	cpmu_vid_attr,
> +	cpmu_threshold_attr,
> +	cpmu_invert_attr,
> +	cpmu_edge_attr,
> +	cpmu_hdm_filter_en_attr,
> +	cpmu_hdm_attr,
> +};
> +
> +static struct attribute *cpmu_format_attr[] = {
> +	[cpmu_mask_attr] = CPMU_FORMAT_ATTR(mask, "config:0-31"),
> +	[cpmu_gid_attr] = CPMU_FORMAT_ATTR(gid, "config:32-47"),
> +	[cpmu_vid_attr] = CPMU_FORMAT_ATTR(vid, "config:48-63"),
> +	[cpmu_threshold_attr] = CPMU_FORMAT_ATTR(threshold, "config1:0-15"),
> +	[cpmu_invert_attr] = CPMU_FORMAT_ATTR(invert, "config1:16"),
> +	[cpmu_edge_attr] = CPMU_FORMAT_ATTR(edge, "config1:17"),
> +	[cpmu_hdm_filter_en_attr] = CPMU_FORMAT_ATTR(hdm_filter_en, "config1:18"),
> +	[cpmu_hdm_attr] = CPMU_FORMAT_ATTR(hdm, "config2:0-15"),
> +	NULL
> +};

Most of this is brand new ABI to me, so I leave it to perf folks to
check for correctness.

> +
> +#define CPMU_ATTR_CONFIG_MASK_MSK	GENMASK_ULL(63, 48)
> +#define CPMU_ATTR_CONFIG_GID_MSK	GENMASK_ULL(47, 32)
> +#define CPMU_ATTR_CONFIG_VID_MSK	GENMASK_ULL(63, 48)
> +#define CPMU_ATTR_CONFIG1_THRESHOLD_MSK	GENMASK_ULL(15, 0)
> +#define CPMU_ATTR_CONFIG1_INVERT_MSK	BIT(16)
> +#define CPMU_ATTR_CONFIG1_EDGE_MSK	BIT(17)
> +#define CPMU_ATTR_CONFIG1_FILTER_EN_MSK	BIT(18)
> +#define CPMU_ATTR_CONFIG2_HDM_MSK	GENMASK(15, 0)
> +
> +static umode_t cpmu_format_is_visible(struct kobject *kobj, struct attribute *attr, int a)
> +{
> +	struct device *dev = kobj_to_dev(kobj);
> +	struct cpmu_info *info = dev_get_drvdata(dev);
> +
> +	/*
> +	 * Filter capability at the CPMU level, so hide the attributes if the particular
> +	 * filter is not supported.
> +	 */
> +	if (attr == cpmu_format_attr[cpmu_hdm_filter_en_attr] ||
> +	    attr == cpmu_format_attr[cpmu_hdm_attr]) {
> +		if (info->filter_hdm)
> +			return 0444;
> +		else
> +			return 0;
> +	} else {
> +		return 0444;
> +	}
> +}

Maybe simplify to:

        if (!info->filter_hdm &&
            (attr == cpmu_format_attr[cpmu_hdm_filter_en_attr] ||
             attr == cpmu_format_attr[cpmu_hdm_attr]))
                return 0;
        return attr->mode;

> +
> +static const struct attribute_group cpmu_format_group = {
> +	.name = "format",
> +	.attrs = cpmu_format_attr,
> +	.is_visible = cpmu_format_is_visible,
> +};
> +
> +static u32 cpmu_config_get_mask(struct perf_event *event)
> +{
> +	return FIELD_GET(CPMU_ATTR_CONFIG_MASK_MSK, event->attr.config);
> +}
> +
> +static u16 cpmu_config_get_gid(struct perf_event *event)
> +{
> +	return FIELD_GET(CPMU_ATTR_CONFIG_GID_MSK, event->attr.config);
> +}
> +
> +static u16 cpmu_config_get_vid(struct perf_event *event)
> +{
> +	return FIELD_GET(CPMU_ATTR_CONFIG_VID_MSK, event->attr.config);
> +}
> +
> +static u8 cpmu_config1_get_threshold(struct perf_event *event)
> +{
> +	return FIELD_GET(CPMU_ATTR_CONFIG1_THRESHOLD_MSK, event->attr.config1);
> +}
> +
> +static bool cpmu_config1_get_invert(struct perf_event *event)
> +{
> +	return FIELD_GET(CPMU_ATTR_CONFIG1_INVERT_MSK, event->attr.config1);
> +}
> +
> +static bool cpmu_config1_get_edge(struct perf_event *event)
> +{
> +	return FIELD_GET(CPMU_ATTR_CONFIG1_EDGE_MSK, event->attr.config1);
> +}
> +
> +/*
> + * CPMU specification allows for 8 filters, each with a 16 bit value...
> + * So we need to find 8x16bits to store it in.
> + * As the value used for disable is 0xffff, a separate enable switch
> + * is needed.
> + */
> +
> +static bool cpmu_config1_hdm_filter_en(struct perf_event *event)
> +{
> +	return FIELD_GET(CPMU_ATTR_CONFIG1_FILTER_EN_MSK, event->attr.config1);
> +}
> +
> +static u16 cpmu_config2_get_hdm_decoder(struct perf_event *event)
> +{
> +	return FIELD_GET(CPMU_ATTR_CONFIG2_HDM_MSK, event->attr.config2);
> +}
> +
> +static ssize_t cpmu_event_sysfs_show(struct device *dev,
> +				     struct device_attribute *attr, char *buf)
> +{
> +	struct perf_pmu_events_attr *pmu_attr =
> +		container_of(attr, struct perf_pmu_events_attr, attr);
> +
> +	return sysfs_emit(buf, "config=%#llx\n", pmu_attr->id);
> +}
> +
> +#define CPMU_PMU_EVENT_ATTR(_name, _vid, _gid, _msk)			\
> +	PMU_EVENT_ATTR_ID(_name, cpmu_event_sysfs_show,			\
> +			  ((u64)(_vid) << 48) | ((u64)(_gid) << 32) | (u64)(_msk))
> +
> +/* For CXL spec defined events */
> +#define CPMU_PMU_EVENT_CXL_ATTR(_name, _gid, _msk) \
> +	CPMU_PMU_EVENT_ATTR(_name, PCI_DVSEC_VENDOR_ID_CXL, _gid, _msk)
> +
> +static struct attribute *cpmu_event_attrs[] = {
> +	CPMU_PMU_EVENT_CXL_ATTR(clock_ticks,			CPMU_GID_CLOCK_TICKS, BIT(0)),
> +	/* CXL rev 3.0 Table 3-17 - Device to Host Requests */
> +	CPMU_PMU_EVENT_CXL_ATTR(d2h_req_rdcurr,			CPMU_GID_D2H_REQ, BIT(1)),
> +	CPMU_PMU_EVENT_CXL_ATTR(d2h_req_rdown,			CPMU_GID_D2H_REQ, BIT(2)),
> +	CPMU_PMU_EVENT_CXL_ATTR(d2h_req_rdshared,		CPMU_GID_D2H_REQ, BIT(3)),
> +	CPMU_PMU_EVENT_CXL_ATTR(d2h_req_rdany,			CPMU_GID_D2H_REQ, BIT(4)),
> +	CPMU_PMU_EVENT_CXL_ATTR(d2h_req_rdownnodata,		CPMU_GID_D2H_REQ, BIT(5)),
> +	CPMU_PMU_EVENT_CXL_ATTR(d2h_req_itomwr,			CPMU_GID_D2H_REQ, BIT(6)),
> +	CPMU_PMU_EVENT_CXL_ATTR(d2h_req_wrcurr,			CPMU_GID_D2H_REQ, BIT(7)),
> +	CPMU_PMU_EVENT_CXL_ATTR(d2h_req_clflush,		CPMU_GID_D2H_REQ, BIT(8)),
> +	CPMU_PMU_EVENT_CXL_ATTR(d2h_req_cleanevict,		CPMU_GID_D2H_REQ, BIT(9)),
> +	CPMU_PMU_EVENT_CXL_ATTR(d2h_req_dirtyevict,		CPMU_GID_D2H_REQ, BIT(10)),
> +	CPMU_PMU_EVENT_CXL_ATTR(d2h_req_cleanevictnodata,	CPMU_GID_D2H_REQ, BIT(11)),
> +	CPMU_PMU_EVENT_CXL_ATTR(d2h_req_wowrinv,		CPMU_GID_D2H_REQ, BIT(12)),
> +	CPMU_PMU_EVENT_CXL_ATTR(d2h_req_wowrinvf,		CPMU_GID_D2H_REQ, BIT(13)),
> +	CPMU_PMU_EVENT_CXL_ATTR(d2h_req_wrinv,			CPMU_GID_D2H_REQ, BIT(14)),
> +	CPMU_PMU_EVENT_CXL_ATTR(d2h_req_cacheflushed,		CPMU_GID_D2H_REQ, BIT(16)),
> +	/* CXL rev 3.0 Table 3-20 - D2H Repsonse Encodings */
> +	CPMU_PMU_EVENT_CXL_ATTR(d2h_rsp_rspihiti,		CPMU_GID_D2H_RSP, BIT(4)),
> +	CPMU_PMU_EVENT_CXL_ATTR(d2h_rsp_rspvhitv,		CPMU_GID_D2H_RSP, BIT(6)),
> +	CPMU_PMU_EVENT_CXL_ATTR(d2h_rsp_rspihitse,		CPMU_GID_D2H_RSP, BIT(5)),
> +	CPMU_PMU_EVENT_CXL_ATTR(d2h_rsp_rspshitse,		CPMU_GID_D2H_RSP, BIT(1)),
> +	CPMU_PMU_EVENT_CXL_ATTR(d2h_rsp_rspsfwdm,		CPMU_GID_D2H_RSP, BIT(7)),
> +	CPMU_PMU_EVENT_CXL_ATTR(d2h_rsp_rspifwdm,		CPMU_GID_D2H_RSP, BIT(15)),
> +	CPMU_PMU_EVENT_CXL_ATTR(d2h_rsp_rspvfwdv,		CPMU_GID_D2H_RSP, BIT(22)),
> +	/* CXL rev 3.0 Table 3-21 - CXL.cache - Mapping of H2D Requests to D2H Responses */
> +	CPMU_PMU_EVENT_CXL_ATTR(h2d_req_snpdata,		CPMU_GID_H2D_REQ, BIT(1)),
> +	CPMU_PMU_EVENT_CXL_ATTR(h2d_req_snpinv,			CPMU_GID_H2D_REQ, BIT(2)),
> +	CPMU_PMU_EVENT_CXL_ATTR(h2d_req_snpcur,			CPMU_GID_H2D_REQ, BIT(3)),
> +	/* CXL rev 3.0 Table 3-22 - H2D Response Opcode Encodings */
> +	CPMU_PMU_EVENT_CXL_ATTR(h2d_rsp_writepull,		CPMU_GID_H2D_RSP, BIT(1)),
> +	CPMU_PMU_EVENT_CXL_ATTR(h2d_rsp_go,			CPMU_GID_H2D_RSP, BIT(4)),
> +	CPMU_PMU_EVENT_CXL_ATTR(h2d_rsp_gowritepull,		CPMU_GID_H2D_RSP, BIT(5)),
> +	CPMU_PMU_EVENT_CXL_ATTR(h2d_rsp_extcmp,			CPMU_GID_H2D_RSP, BIT(6)),
> +	CPMU_PMU_EVENT_CXL_ATTR(h2d_rsp_gowritepulldrop,	CPMU_GID_H2D_RSP, BIT(8)),
> +	CPMU_PMU_EVENT_CXL_ATTR(h2d_rsp_fastgowritepull,	CPMU_GID_H2D_RSP, BIT(13)),
> +	CPMU_PMU_EVENT_CXL_ATTR(h2d_rsp_goerrwritepull,		CPMU_GID_H2D_RSP, BIT(15)),
> +	/* CXL rev 3.0 Table 13-5 directly lists these */
> +	CPMU_PMU_EVENT_CXL_ATTR(cachedata_d2h_data,		CPMU_GID_CACHE_DATA, BIT(0)),
> +	CPMU_PMU_EVENT_CXL_ATTR(cachedata_h2d_data,		CPMU_GID_CACHE_DATA, BIT(1)),
> +	/* CXL rev 3.0 Table 3-29 M2S Req Memory Opcodes */
> +	CPMU_PMU_EVENT_CXL_ATTR(m2s_req_meminv,			CPMU_GID_M2S_REQ, BIT(0)),
> +	CPMU_PMU_EVENT_CXL_ATTR(m2s_req_memrd,			CPMU_GID_M2S_REQ, BIT(1)),
> +	CPMU_PMU_EVENT_CXL_ATTR(m2s_req_memrddata,		CPMU_GID_M2S_REQ, BIT(2)),
> +	CPMU_PMU_EVENT_CXL_ATTR(m2s_req_memrdfwd,		CPMU_GID_M2S_REQ, BIT(3)),
> +	CPMU_PMU_EVENT_CXL_ATTR(m2s_req_memwrfwd,		CPMU_GID_M2S_REQ, BIT(4)),
> +	CPMU_PMU_EVENT_CXL_ATTR(m2s_req_memspecrd,		CPMU_GID_M2S_REQ, BIT(8)),
> +	CPMU_PMU_EVENT_CXL_ATTR(m2s_req_meminvnt,		CPMU_GID_M2S_REQ, BIT(9)),
> +	CPMU_PMU_EVENT_CXL_ATTR(m2s_req_memcleanevict,		CPMU_GID_M2S_REQ, BIT(10)),
> +	/* CXL rev 3.0 Table 3-35 M2S RwD Memory Opcodes */
> +	CPMU_PMU_EVENT_CXL_ATTR(m2s_rwd_memwr,			CPMU_GID_M2S_RWD, BIT(1)),
> +	CPMU_PMU_EVENT_CXL_ATTR(m2s_rwd_memwrptl,		CPMU_GID_M2S_RWD, BIT(2)),
> +	CPMU_PMU_EVENT_CXL_ATTR(m2s_rwd_biconflict,		CPMU_GID_M2S_RWD, BIT(4)),
> +	/* CXL rev 3.0 Table 3-38 M2S BIRsp Memory Opcodes */
> +	CPMU_PMU_EVENT_CXL_ATTR(m2s_birsp_i,			CPMU_GID_M2S_BIRSP, BIT(0)),
> +	CPMU_PMU_EVENT_CXL_ATTR(m2s_birsp_s,			CPMU_GID_M2S_BIRSP, BIT(1)),
> +	CPMU_PMU_EVENT_CXL_ATTR(m2s_birsp_e,			CPMU_GID_M2S_BIRSP, BIT(2)),
> +	CPMU_PMU_EVENT_CXL_ATTR(m2s_birsp_iblk,			CPMU_GID_M2S_BIRSP, BIT(4)),
> +	CPMU_PMU_EVENT_CXL_ATTR(m2s_birsp_sblk,			CPMU_GID_M2S_BIRSP, BIT(5)),
> +	CPMU_PMU_EVENT_CXL_ATTR(m2s_birsp_eblk,			CPMU_GID_M2S_BIRSP, BIT(6)),
> +	/* CXL rev 3.0 Table 3-40 S2M BISnp Opcodes */
> +	CPMU_PMU_EVENT_CXL_ATTR(s2m_bisnp_cur,			CPMU_GID_S2M_BISNP, BIT(0)),
> +	CPMU_PMU_EVENT_CXL_ATTR(s2m_bisnp_data,			CPMU_GID_S2M_BISNP, BIT(1)),
> +	CPMU_PMU_EVENT_CXL_ATTR(s2m_bisnp_inv,			CPMU_GID_S2M_BISNP, BIT(2)),
> +	CPMU_PMU_EVENT_CXL_ATTR(s2m_bisnp_curblk,		CPMU_GID_S2M_BISNP, BIT(4)),
> +	CPMU_PMU_EVENT_CXL_ATTR(s2m_bisnp_datblk,		CPMU_GID_S2M_BISNP, BIT(5)),
> +	CPMU_PMU_EVENT_CXL_ATTR(s2m_bisnp_invblk,		CPMU_GID_S2M_BISNP, BIT(6)),
> +	/* CXL rev 3.0 Table 3-43 S2M NDR Opcopdes */
> +	CPMU_PMU_EVENT_CXL_ATTR(s2m_ndr_cmp,			CPMU_GID_S2M_NDR, BIT(0)),
> +	CPMU_PMU_EVENT_CXL_ATTR(s2m_ndr_cmps,			CPMU_GID_S2M_NDR, BIT(1)),
> +	CPMU_PMU_EVENT_CXL_ATTR(s2m_ndr_cmpe,			CPMU_GID_S2M_NDR, BIT(2)),
> +	CPMU_PMU_EVENT_CXL_ATTR(s2m_ndr_biconflictack,		CPMU_GID_S2M_NDR, BIT(3)),
> +	/* CXL rev 3.0 Table 3-46 S2M DRS opcodes */
> +	CPMU_PMU_EVENT_CXL_ATTR(s2m_drs_memdata,		CPMU_GID_S2M_DRS, BIT(0)),
> +	CPMU_PMU_EVENT_CXL_ATTR(s2m_drs_memdatanxm,		CPMU_GID_S2M_DRS, BIT(1)),
> +	/* CXL rev 3.0 Table 13-5 directly lists these */
> +	CPMU_PMU_EVENT_CXL_ATTR(ddr_act,			CPMU_GID_DDR, BIT(0)),
> +	CPMU_PMU_EVENT_CXL_ATTR(ddr_pre,			CPMU_GID_DDR, BIT(1)),
> +	CPMU_PMU_EVENT_CXL_ATTR(ddr_casrd,			CPMU_GID_DDR, BIT(2)),
> +	CPMU_PMU_EVENT_CXL_ATTR(ddr_caswr,			CPMU_GID_DDR, BIT(3)),
> +	CPMU_PMU_EVENT_CXL_ATTR(ddr_refresh,			CPMU_GID_DDR, BIT(4)),
> +	CPMU_PMU_EVENT_CXL_ATTR(ddr_selfrefreshent,		CPMU_GID_DDR, BIT(5)),
> +	CPMU_PMU_EVENT_CXL_ATTR(ddr_rfm,			CPMU_GID_DDR, BIT(6)),
> +	NULL
> +};
> +
> +static struct cpmu_event *cpmu_find_fixed_counter_event(struct cpmu_info *info,
> +							int vid, int gid, int msk)
> +{
> +	struct cpmu_event *cpmu_ev;
> +
> +	list_for_each_entry(cpmu_ev, &info->events_fixed, node) {
> +		if (vid != cpmu_ev->vid || gid != cpmu_ev->gid)
> +			continue;
> +
> +		/* Precise match for fixed counter */
> +		if (msk == cpmu_ev->msk)
> +			return cpmu_ev;

It looks like the lookup parameters fit in 64-bits which if using an
xarray could do a direct lookup (assuming this driver 'depends on 64BIT'
which is not unreasonable).

> +	}
> +
> +	return ERR_PTR(-EINVAL);
> +}
> +
> +static struct cpmu_event *cpmu_find_config_counter_event(struct cpmu_info *info,
> +							 int vid, int gid, int msk)
> +{
> +	struct cpmu_event *cpmu_ev;
> +
> +	list_for_each_entry(cpmu_ev, &info->events_configurable, node) {
> +		if (vid != cpmu_ev->vid || gid != cpmu_ev->gid)
> +			continue;
> +
> +		/* Request mask must be subset of supported */
> +		if (msk & ~cpmu_ev->msk)
> +			continue;
> +
> +		return cpmu_ev;
> +	}
> +
> +	return ERR_PTR(-EINVAL);
> +}
> +
> +static umode_t cpmu_event_is_visible(struct kobject *kobj, struct attribute *attr, int a)
> +{
> +	struct device_attribute *dev_attr = container_of(attr, struct device_attribute, attr);
> +	struct perf_pmu_events_attr *pmu_attr =
> +		container_of(dev_attr, struct perf_pmu_events_attr, attr);
> +	struct device *dev = kobj_to_dev(kobj);
> +	struct cpmu_info *info = dev_get_drvdata(dev);
> +	int vid = FIELD_GET(CPMU_ATTR_CONFIG_VID_MSK, pmu_attr->id);
> +	int gid = FIELD_GET(CPMU_ATTR_CONFIG_GID_MSK, pmu_attr->id);
> +	int msk = FIELD_GET(CPMU_ATTR_CONFIG_MASK_MSK, pmu_attr->id);
> +
> +	if (!IS_ERR(cpmu_find_fixed_counter_event(info, vid, gid, msk)))
> +		return attr->mode;
> +
> +	if (!IS_ERR(cpmu_find_config_counter_event(info, vid, gid, msk)))
> +		return attr->mode;
> +
> +	return 0;
> +}
> +
> +static const struct attribute_group cpmu_events = {
> +	.name = "events",
> +	.attrs = cpmu_event_attrs,
> +	.is_visible = cpmu_event_is_visible,
> +};
> +
> +static ssize_t cpumask_show(struct device *dev, struct device_attribute *attr,
> +			    char *buf)
> +{
> +	struct cpmu_info *info = dev_get_drvdata(dev);
> +
> +	return cpumap_print_to_pagebuf(true, buf, cpumask_of(info->on_cpu));
> +}
> +static DEVICE_ATTR_RO(cpumask);
> +
> +static struct attribute *cpmu_cpumask_attrs[] = {
> +	&dev_attr_cpumask.attr,
> +	NULL
> +};
> +
> +static const struct attribute_group cpmu_cpumask_group = {
> +	.attrs = cpmu_cpumask_attrs,
> +};
> +
> +static const struct attribute_group *cpmu_attr_groups[] = {
> +	&cpmu_events,
> +	&cpmu_format_group,
> +	&cpmu_cpumask_group,
> +	NULL
> +};
> +
> +/* If counter_idx == NULL, don't try to allocate a counter. */
> +static int cpmu_get_event_idx(struct perf_event *event, int *counter_idx, int *event_idx)
> +{
> +	struct cpmu_info *info = pmu_to_cpmu_info(event->pmu);
> +	DECLARE_BITMAP(configurable_and_free, CPMU_MAX_COUNTERS);
> +	struct cpmu_event *cpmu_ev;
> +	u32 mask;
> +	u16 gid, vid;
> +	int i;
> +
> +	vid = cpmu_config_get_vid(event);
> +	gid = cpmu_config_get_gid(event);
> +	mask = cpmu_config_get_mask(event);
> +
> +	cpmu_ev = cpmu_find_fixed_counter_event(info, vid, gid, mask);
> +	if (!IS_ERR(cpmu_ev)) {
> +		if (!counter_idx)
> +			return 0;
> +		if (!test_bit(cpmu_ev->counter_idx, info->used_counter_bm)) {
> +			*counter_idx = cpmu_ev->counter_idx;
> +			return 0;
> +		}
> +		/* Fixed counter is in use, but maybe a configurable one? */
> +	}
> +
> +	cpmu_ev = cpmu_find_config_counter_event(info, vid, gid, mask);
> +	if (!IS_ERR(cpmu_ev)) {
> +		if (!counter_idx)
> +			return 0;
> +
> +		bitmap_andnot(configurable_and_free, info->conf_counter_bm,
> +			info->used_counter_bm, CPMU_MAX_COUNTERS);
> +
> +		i = find_first_bit(configurable_and_free, CPMU_MAX_COUNTERS);
> +		if (i == CPMU_MAX_COUNTERS)
> +			return -EINVAL;
> +
> +		*counter_idx = i;
> +		return 0;
> +	}
> +
> +	return -EINVAL;
> +}
> +
> +static int cpmu_event_init(struct perf_event *event)
> +{
> +	struct cpmu_info *info = pmu_to_cpmu_info(event->pmu);
> +
> +	event->cpu = info->on_cpu;
> +	/* Top level type sanity check - is this a Hardware Event being requested */
> +	if (event->attr.type != event->pmu->type)
> +		return -ENOENT;
> +
> +	if (is_sampling_event(event) || event->attach_state & PERF_ATTACH_TASK)
> +		return -EOPNOTSUPP;
> +	/* TODO: Validation of any filter */
> +
> +	/*
> +	 * Verify that it is possible to count what was requested. Either must
> +	 * be a fixed counter that is a precise match or a configurable counter
> +	 * where this is a subset.
> +	 */
> +	return cpmu_get_event_idx(event, NULL, NULL);
> +}
> +
> +static void cpmu_pmu_enable(struct pmu *pmu)
> +{
> +	struct cpmu_info *info = pmu_to_cpmu_info(pmu);
> +	void __iomem *base = info->base;
> +
> +	/* We don't have a global enable, but we 'might' have a global freeze which we can use */
> +	if (info->freeze_for_enable) {
> +		/* Can assume frozen at this stage */
> +		writeq(0, base + CPMU_FREEZE_REG);
> +
> +		return;
> +	}
> +}
> +
> +static void cpmu_pmu_disable(struct pmu *pmu)
> +{
> +	struct cpmu_info *info = pmu_to_cpmu_info(pmu);
> +	void __iomem *base = info->base;
> +
> +	if (info->freeze_for_enable) {
> +		/*
> +		 * Whilst bits above number of counters are RsvdZ
> +		 * they are unlikely to be repurposed given
> +		 * number of counters is allowed to be 64 leaving
> +		 * no reserved bits.  Hence this is only slightly
> +		 * naughty.
> +		 */
> +		writeq(GENMASK_ULL(63, 0), base + CPMU_FREEZE_REG);
> +		return;
> +	}
> +}

These can be swapped out for versions that do nothing in the
freeze_for_enable == false case when that support arrives, otherwise
these can be simplified because the check was resolved at init time.

> +
> +static void cpmu_event_start(struct perf_event *event, int flags)
> +{
> +	struct cpmu_info *info = pmu_to_cpmu_info(event->pmu);
> +	struct hw_perf_event *hwc = &event->hw;
> +	void __iomem *base = info->base;
> +	u64 cfg;
> +
> +	if (WARN_ON_ONCE(!(hwc->state & PERF_HES_STOPPED)))
> +		return;
> +
> +	WARN_ON_ONCE(!(hwc->state & PERF_HES_UPTODATE));

Maybe a comment about why these warns will likely never fire in practice?

> +	hwc->state = 0;
> +
> +	/*
> +	 * Currently only hdm filter control is implemnted, this code will
> +	 * want generalizing when more filters are added.
> +	 */
> +	if (info->filter_hdm) {
> +		if (cpmu_config1_hdm_filter_en(event))
> +			cfg = cpmu_config2_get_hdm_decoder(event);
> +		else
> +			cfg = GENMASK(15, 0); /* No filtering if 0xFFFF_FFFF */
> +		writeq(cfg, base + CPMU_FILTER_CFG_REG(hwc->idx, 0));
> +	}
> +
> +	cfg = readq(base + CPMU_COUNTER_CFG_REG(hwc->idx));
> +	cfg |= FIELD_PREP(CPMU_COUNTER_CFG_INT_ON_OVRFLW, 1);
> +	cfg |= FIELD_PREP(CPMU_COUNTER_CFG_ENABLE, 1);
> +	cfg |= FIELD_PREP(CPMU_COUNTER_CFG_EDGE, cpmu_config1_get_edge(event) ? 1 : 0);
> +	cfg |= FIELD_PREP(CPMU_COUNTER_CFG_INVERT, cpmu_config1_get_invert(event) ? 1 : 0);
> +
> +	/* Fixed purpose counters have next two fields RO */
> +	if (test_bit(hwc->idx, info->conf_counter_bm)) {
> +		cfg |= FIELD_PREP(CPMU_COUNTER_CFG_EVENT_GRP_ID_IDX_MSK, hwc->event_base);
> +		cfg |= FIELD_PREP(CPMU_COUNTER_CFG_EVENTS_MSK, cpmu_config_get_mask(event));
> +	}
> +	cfg &= ~CPMU_COUNTER_CFG_THRESHOLD_MSK;
> +	/*
> +	 * For events that generate only 1 count per clock the CXL 3.0 spec
> +	 * states the threshold shall be set to 1 but if set to 0 it will
> +	 * count the raw value anwyay?
> +	 * There is no definition of what events will count multiple per cycle
> +	 * and hence to which non 1 values of threshold can apply.
> +	 * (CXL 3.0 8.2.7.2.1 Counter Configuration - threshold field definition)
> +	 */
> +	cfg |= FIELD_PREP(CPMU_COUNTER_CFG_THRESHOLD_MSK,
> +			  cpmu_config1_get_threshold(event));
> +	writeq(cfg, base + CPMU_COUNTER_CFG_REG(hwc->idx));
> +
> +	local64_set(&hwc->prev_count, 0);
> +	writeq(0, base + CPMU_COUNTER_REG(hwc->idx));
> +
> +	perf_event_update_userpage(event);
> +}
> +
> +static u64 cpmu_read_counter(struct perf_event *event)
> +{
> +	struct cpmu_info *info = pmu_to_cpmu_info(event->pmu);
> +	void __iomem *base = info->base;
> +
> +	return readq(base + CPMU_COUNTER_REG(event->hw.idx));
> +}
> +
> +static void __cpmu_read(struct perf_event *event, bool overflow)
> +{
> +	struct cpmu_info *info = pmu_to_cpmu_info(event->pmu);
> +	struct hw_perf_event *hwc = &event->hw;
> +	u64 new_cnt, prev_cnt, delta;
> +
> +	do {
> +		prev_cnt = local64_read(&hwc->prev_count);
> +		new_cnt = cpmu_read_counter(event);
> +	} while (local64_cmpxchg(&hwc->prev_count, prev_cnt, new_cnt) != prev_cnt);
> +
> +	/*
> +	 * If we know an overflow occur then take that into account.
> +	 * Note counter is not reset as that would lose events
> +	 */
> +	delta = (new_cnt - prev_cnt) & GENMASK_ULL(info->counter_width - 1, 0);
> +	if (overflow && delta < GENMASK_ULL(info->counter_width - 1, 0))
> +		delta += (1UL << info->counter_width);
> +
> +	local64_add(delta, &event->count);
> +}
> +
> +static void cpmu_read(struct perf_event *event)
> +{
> +	__cpmu_read(event, false);
> +}
> +
> +static void cpmu_event_stop(struct perf_event *event, int flags)
> +{
> +	struct cpmu_info *info = pmu_to_cpmu_info(event->pmu);
> +	void __iomem *base = info->base;
> +	struct hw_perf_event *hwc = &event->hw;
> +	u64 cfg;
> +
> +	cpmu_read(event);
> +	WARN_ON_ONCE(hwc->state & PERF_HES_STOPPED);
> +	hwc->state |= PERF_HES_STOPPED;
> +
> +	cfg = readq(base + CPMU_COUNTER_CFG_REG(hwc->idx));
> +	cfg &= ~(FIELD_PREP(CPMU_COUNTER_CFG_INT_ON_OVRFLW, 1) |
> +		 FIELD_PREP(CPMU_COUNTER_CFG_ENABLE, 1));
> +	writeq(cfg, base + CPMU_COUNTER_CFG_REG(hwc->idx));
> +
> +	hwc->state |= PERF_HES_UPTODATE;
> +}
> +
> +/*
> + * Reset ensures no possibility of any information leaking to wrong
> + * counter. Note that all fields written during start()
> + */
> +static void cpmu_reset_counter(struct cpmu_info *info, int idx)
> +{
> +	void __iomem *base = info->base;
> +
> +	/* Much of this register is read only */
> +	writeq(0, base + CPMU_EVENT_CAP_REG(idx));
> +	/* Filters are not per counter, so no reset here */
> +	writeq(0, base + CPMU_COUNTER_REG(idx));
> +}
> +
> +static int cpmu_event_add(struct perf_event *event, int flags)
> +{
> +	struct cpmu_info *info = pmu_to_cpmu_info(event->pmu);
> +	struct hw_perf_event *hwc = &event->hw;
> +	int idx, rc;
> +	int event_idx = 0;
> +
> +	hwc->state = PERF_HES_STOPPED | PERF_HES_UPTODATE;
> +
> +	rc = cpmu_get_event_idx(event, &idx, &event_idx);
> +	if (rc < 0)
> +		return rc;
> +
> +	hwc->idx = idx;
> +
> +	/* Only set for configurable counters */
> +	hwc->event_base = event_idx;
> +	info->hw_events[idx] = event;
> +	set_bit(idx, info->used_counter_bm);
> +
> +	cpmu_reset_counter(info, idx);
> +
> +	if (flags & PERF_EF_START)
> +		cpmu_event_start(event, PERF_EF_RELOAD);
> +
> +	return 0;
> +}
> +
> +static void cpmu_event_del(struct perf_event *event, int flags)
> +{
> +	struct cpmu_info *info = pmu_to_cpmu_info(event->pmu);
> +	struct hw_perf_event *hwc = &event->hw;
> +
> +	cpmu_event_stop(event, PERF_EF_UPDATE);
> +	clear_bit(hwc->idx, info->used_counter_bm);
> +	info->hw_events[hwc->idx] = NULL;
> +	perf_event_update_userpage(event);
> +}
> +
> +static irqreturn_t cpmu_irq(int irq, void *data)
> +{
> +	struct cpmu_info *info = data;
> +	void __iomem *base = info->base;
> +	u64 overflowed;
> +	DECLARE_BITMAP(overflowedbm, 64);
> +	int i;
> +
> +	overflowed = readq(base + CPMU_OVERFLOW_REG);
> +
> +	/* Interrupt may be shared, so maybe it isn't ours */
> +	if (!overflowed)
> +		return IRQ_NONE;
> +
> +	bitmap_from_arr64(overflowedbm, &overflowed, 64);
> +	for_each_set_bit(i, overflowedbm, info->num_counters) {
> +		struct perf_event *event = info->hw_events[i];
> +
> +		if (!event) {
> +			dev_dbg(info->pmu.dev,
> +				"overflow but on non enabled counter %d\n", i);
> +			continue;
> +		}
> +
> +		__cpmu_read(event, true);
> +	}
> +
> +	writeq(overflowed, base + CPMU_OVERFLOW_REG);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +static int cxl_cpmu_probe(struct device *dev)
> +{
> +	struct cxl_cpmu *cpmu = to_cxl_cpmu(dev);
> +	struct pci_dev *pdev = to_pci_dev(dev->parent);
> +	struct cpmu_info *info;
> +	char *irq_name;
> +	int rc, irq;
> +
> +	info = devm_kzalloc(dev, sizeof(*info), GFP_KERNEL);
> +	if (!info)
> +		return -ENOMEM;
> +
> +	INIT_LIST_HEAD(&info->events_fixed);
> +	INIT_LIST_HEAD(&info->events_configurable);
> +
> +	info->base = cpmu->base;
> +
> +	info->on_cpu = -1;
> +	rc = cpmu_parse_caps(dev, info);
> +	if (rc)
> +		return rc;
> +
> +	info->hw_events = devm_kcalloc(dev, sizeof(*info->hw_events),
> +				       info->num_counters, GFP_KERNEL);
> +	if (!info->hw_events)
> +		return -ENOMEM;
> +
> +	info->pmu = (struct pmu) {
> +		.name = dev_name(dev),
> +		.parent = dev,
> +		.module = THIS_MODULE,
> +		.event_init = cpmu_event_init,
> +		.pmu_enable = cpmu_pmu_enable,
> +		.pmu_disable = cpmu_pmu_disable,
> +		.add = cpmu_event_add,
> +		.del = cpmu_event_del,
> +		.start = cpmu_event_start,
> +		.stop = cpmu_event_stop,
> +		.read = cpmu_read,
> +		.task_ctx_nr = perf_invalid_context,
> +		.attr_groups = cpmu_attr_groups,
> +		.capabilities = PERF_PMU_CAP_NO_EXCLUDE,
> +	};
> +
> +	if (info->irq <= 0)
> +		return -EINVAL;
> +
> +	rc = pci_irq_vector(pdev, info->irq);
> +	if (rc < 0)
> +		return rc;
> +	irq = rc;
> +
> +	irq_name = devm_kasprintf(dev, GFP_KERNEL, "%s_overflow\n", dev_name(dev));
> +	if (!irq_name)
> +		return -ENOMEM;
> +
> +	rc = devm_request_irq(dev, irq, cpmu_irq, IRQF_SHARED, irq_name, info);

This also wants IRQF_ONESHOT, see:

5a84711fd734 cxl/pci: Fix irq oneshot expectations


> +	if (rc)
> +		return rc;
> +	info->irq = irq;
> +
> +	rc = cpuhp_state_add_instance(cpmu_cpuhp_state_num, &info->node);
> +	if (rc)
> +		return rc;
> +
> +	rc = perf_pmu_register(&info->pmu, info->pmu.name, -1);
> +	if (rc)
> +		return rc;
> +
> +	dev_set_drvdata(dev, info);

Is it really the case that drvdata can be set after the pmu is already
registered and live, or maybe just getting lucky with accessing the ABI
after probe returns?

> +
> +	return 0;
> +}
> +
> +static void cxl_cpmu_remove(struct device *dev)
> +{
> +	struct cpmu_info *info = dev_get_drvdata(dev);
> +
> +	perf_pmu_unregister(&info->pmu);
> +	cpuhp_state_remove_instance_nocalls(cpmu_cpuhp_state_num, &info->node);

How about add devm_add_action_or_reset() calls for these and delete
cxl_cpmu_remove()?

> +}
> +
> +static struct cxl_driver cxl_cpmu_driver = {
> +	.name = "cxl_cpmu",
> +	.probe = cxl_cpmu_probe,
> +	.remove = cxl_cpmu_remove,
> +	.id = CXL_DEVICE_CPMU,
> +};
> +
> +static int cpmu_online_cpu(unsigned int cpu, struct hlist_node *node)
> +{
> +	struct cpmu_info *info = hlist_entry_safe(node, struct cpmu_info, node);
> +
> +	if (info->on_cpu != -1)
> +		return 0;
> +
> +	info->on_cpu = cpu;
> +	WARN_ON(irq_set_affinity(info->irq, cpumask_of(cpu)));

Is this really a kernel crashable scenario for folks that have
panic_on_warn() set? If it's a "should never" happen type situation then
maybe a comment, otherwise pr_warn().

> +
> +	return 0;
> +}
> +
> +static int cpmu_offline_cpu(unsigned int cpu, struct hlist_node *node)
> +{
> +	struct cpmu_info *info = hlist_entry_safe(node, struct cpmu_info, node);
> +	unsigned int target;
> +
> +	if (info->on_cpu != cpu)
> +		return 0;
> +
> +	info->on_cpu = -1;
> +	target = cpumask_first(cpu_online_mask);
> +	if (target >= nr_cpu_ids) {
> +		dev_err(info->pmu.dev, "Unable to find a suitable CPU\n");
> +		return 0;
> +	}
> +
> +	perf_pmu_migrate_context(&info->pmu, cpu, target);
> +	info->on_cpu = target;
> +	WARN_ON(irq_set_affinity(info->irq, cpumask_of(target)));
> +
> +	return 0;
> +}
> +
> +static __init int cxl_cpmu_init(void)
> +{
> +	int rc;
> +
> +	rc = cpuhp_setup_state_multi(CPUHP_AP_ONLINE_DYN,
> +				     "AP_PERF_CPMU_ONLINE",
> +				     cpmu_online_cpu, cpmu_offline_cpu);
> +	if (rc < 0)
> +		return rc;
> +	cpmu_cpuhp_state_num = rc;
> +
> +	rc = cxl_driver_register(&cxl_cpmu_driver);
> +	if (rc)
> +		cpuhp_remove_multi_state(cpmu_cpuhp_state_num);
> +
> +	return rc;
> +}
> +
> +static __exit void cxl_cpmu_exit(void)
> +{
> +	cxl_driver_unregister(&cxl_cpmu_driver);
> +	cpuhp_remove_multi_state(cpmu_cpuhp_state_num);
> +}
> +
> +MODULE_LICENSE("GPL");
> +MODULE_IMPORT_NS(CXL);
> +module_init(cxl_cpmu_init);
> +module_exit(cxl_cpmu_exit);
> +MODULE_ALIAS_CXL(CXL_DEVICE_CPMU);
> -- 
> 2.37.2
> 

This looks good to me, I'd be happy to take it through the CXL tree when
it finalizes with perf folks acks, just let me know.