[PATCH v3] x86/Hyper-V: Support for free page reporting

From: Sunil Muthuswamy
Date: Wed Jan 06 2021 - 18:21:55 EST

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Linux has support for free page reporting now (36e66c554b5c) for
virtualized environment. On Hyper-V when virtually backed VMs are
configured, Hyper-V will advertise cold memory discard capability,
when supported. This patch adds the support to hook into the free
page reporting infrastructure and leverage the Hyper-V cold memory
discard hint hypercall to report/free these pages back to the host.

Signed-off-by: Sunil Muthuswamy <sunilmut@xxxxxxxxxxxxx>
Tested-by: Matheus Castello <matheus@xxxxxxxxxxxxxxx>
---
In V2:
- Addressed feedback comments
- Added page reporting config option tied to hyper-v balloon config

In V3:
- Addressed feedback from Vitaly
---
arch/x86/hyperv/hv_init.c | 31 +++++++++++
arch/x86/kernel/cpu/mshyperv.c | 6 +-
drivers/hv/Kconfig | 1 +
drivers/hv/hv_balloon.c | 93 +++++++++++++++++++++++++++++++
include/asm-generic/hyperv-tlfs.h | 32 ++++++++++-
include/asm-generic/mshyperv.h | 2 +
6 files changed, 162 insertions(+), 3 deletions(-)

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index e04d90af4c27..5b610e47d091 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -528,3 +528,34 @@ bool hv_is_hibernation_supported(void)
return acpi_sleep_state_supported(ACPI_STATE_S4);
}
EXPORT_SYMBOL_GPL(hv_is_hibernation_supported);
+
+/* Bit mask of the extended capability to query: see HV_EXT_CAPABILITY_xxx */
+bool hv_query_ext_cap(u64 cap_query)
+{
+ u64 *cap;
+ unsigned long flags;
+ u64 ext_cap = 0;
+
+ /*
+ * Querying extended capabilities is an extended hypercall. Check if the
+ * partition supports extended hypercall, first.
+ */
+ if (!(ms_hyperv.priv_high & HV_ENABLE_EXTENDED_HYPERCALLS))
+ return 0;
+
+ /*
+ * Repurpose the input page arg to accept output from Hyper-V for
+ * now because this is the only call that needs output from the
+ * hypervisor. It should be fixed properly by introducing an
+ * output arg once we have more places that require output.
+ */
+ local_irq_save(flags);
+ cap = *(u64 **)this_cpu_ptr(hyperv_pcpu_input_arg);
+ if (hv_do_hypercall(HV_EXT_CALL_QUERY_CAPABILITIES, NULL, cap) ==
+ HV_STATUS_SUCCESS)
+ ext_cap = *cap;
+
+ local_irq_restore(flags);
+ return ext_cap & cap_query;
+}
+EXPORT_SYMBOL_GPL(hv_query_ext_cap);
diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index 05ef1f4550cb..f4c0d69c61ae 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -225,11 +225,13 @@ static void __init ms_hyperv_init_platform(void)
* Extract the features and hints
*/
ms_hyperv.features = cpuid_eax(HYPERV_CPUID_FEATURES);
+ ms_hyperv.priv_high = cpuid_ebx(HYPERV_CPUID_FEATURES);
ms_hyperv.misc_features = cpuid_edx(HYPERV_CPUID_FEATURES);
ms_hyperv.hints = cpuid_eax(HYPERV_CPUID_ENLIGHTMENT_INFO);

- pr_info("Hyper-V: features 0x%x, hints 0x%x, misc 0x%x\n",
- ms_hyperv.features, ms_hyperv.hints, ms_hyperv.misc_features);
+ pr_info("Hyper-V: privilege flags low:0x%x, high:0x%x, hints:0x%x, misc:0x%x\n",
+ ms_hyperv.features, ms_hyperv.priv_high, ms_hyperv.hints,
+ ms_hyperv.misc_features);

ms_hyperv.max_vp_index = cpuid_eax(HYPERV_CPUID_IMPLEMENT_LIMITS);
ms_hyperv.max_lp_index = cpuid_ebx(HYPERV_CPUID_IMPLEMENT_LIMITS);
diff --git a/drivers/hv/Kconfig b/drivers/hv/Kconfig
index 79e5356a737a..66c794d92391 100644
--- a/drivers/hv/Kconfig
+++ b/drivers/hv/Kconfig
@@ -23,6 +23,7 @@ config HYPERV_UTILS
config HYPERV_BALLOON
tristate "Microsoft Hyper-V Balloon driver"
depends on HYPERV
+ select PAGE_REPORTING
help
Select this option to enable Hyper-V Balloon driver.

diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
index 8c471823a5af..c0ff0a48f540 100644
--- a/drivers/hv/hv_balloon.c
+++ b/drivers/hv/hv_balloon.c
@@ -21,6 +21,7 @@
#include <linux/memory.h>
#include <linux/notifier.h>
#include <linux/percpu_counter.h>
+#include <linux/page_reporting.h>

#include <linux/hyperv.h>
#include <asm/hyperv-tlfs.h>
@@ -563,6 +564,10 @@ struct hv_dynmem_device {
* The negotiated version agreed by host.
*/
__u32 version;
+
+#ifdef CONFIG_PAGE_REPORTING
+ struct page_reporting_dev_info pr_dev_info;
+#endif
};

static struct hv_dynmem_device dm_device;
@@ -1568,6 +1573,84 @@ static void balloon_onchannelcallback(void *context)

}

+#ifdef CONFIG_PAGE_REPORTING
+/* Hyper-V only supports reporting 2MB pages or higher */
+#define HV_MIN_PAGE_REPORTING_ORDER 9
+#define HV_MIN_PAGE_REPORTING_LEN (HV_HYP_PAGE_SIZE << HV_MIN_PAGE_REPORTING_ORDER)
+static int hv_free_page_report(struct page_reporting_dev_info *pr_dev_info,
+ struct scatterlist *sgl, unsigned int nents)
+{
+ unsigned long flags;
+ struct hv_memory_hint *hint;
+ int i;
+ u64 status;
+ struct scatterlist *sg;
+
+ WARN_ON_ONCE(nents > HV_MEMORY_HINT_MAX_GPA_PAGE_RANGES);
+ local_irq_save(flags);
+ hint = *(struct hv_memory_hint **)this_cpu_ptr(hyperv_pcpu_input_arg);
+ if (!hint) {
+ local_irq_restore(flags);
+ return -ENOSPC;
+ }
+
+ hint->type = HV_EXT_MEMORY_HEAT_HINT_TYPE_COLD_DISCARD;
+ hint->reserved = 0;
+ for_each_sg(sgl, sg, nents, i) {
+ union hv_gpa_page_range *range;
+
+ range = &hint->ranges[i];
+ range->address_space = 0;
+ /* page reportting only reports 2MB pages or higher */
+ range->page.largepage = 1;
+ range->page.additional_pages =
+ (sg->length / HV_MIN_PAGE_REPORTING_LEN) - 1;
+ range->base_large_pfn =
+ page_to_pfn(sg_page(sg)) >> HV_MIN_PAGE_REPORTING_ORDER;
+ }
+
+ status = hv_do_rep_hypercall(HV_EXT_CALL_MEMORY_HEAT_HINT, nents, 0,
+ hint, NULL);
+ local_irq_restore(flags);
+ if ((status & HV_HYPERCALL_RESULT_MASK) != HV_STATUS_SUCCESS) {
+ pr_err("Cold memory discard hypercall failed with status %llx\n",
+ status);
+ return -EINVAL;
+ }
+
+ return 0;
+}
+
+static void enable_page_reporting(void)
+{
+ int ret;
+
+ BUILD_BUG_ON(pageblock_order < HV_MIN_PAGE_REPORTING_ORDER);
+ if (!hv_query_ext_cap(HV_EXT_CAPABILITY_MEMORY_COLD_DISCARD_HINT)) {
+ pr_debug("Cold memory discard hint not supported by Hyper-V\n");
+ return;
+ }
+
+ BUILD_BUG_ON(PAGE_REPORTING_CAPACITY > HV_MEMORY_HINT_MAX_GPA_PAGE_RANGES);
+ dm_device.pr_dev_info.report = hv_free_page_report;
+ ret = page_reporting_register(&dm_device.pr_dev_info);
+ if (ret < 0) {
+ dm_device.pr_dev_info.report = NULL;
+ pr_err("Failed to enable cold memory discard: %d\n", ret);
+ } else {
+ pr_info("Cold memory discard hint enabled\n");
+ }
+}
+
+static void disable_page_reporting(void)
+{
+ if (dm_device.pr_dev_info.report) {
+ page_reporting_unregister(&dm_device.pr_dev_info);
+ dm_device.pr_dev_info.report = NULL;
+ }
+}
+#endif /* CONFIG_PAGE_REPORTING */
+
static int balloon_connect_vsp(struct hv_device *dev)
{
struct dm_version_request version_req;
@@ -1713,6 +1796,10 @@ static int balloon_probe(struct hv_device *dev,
if (ret != 0)
return ret;

+#ifdef CONFIG_PAGE_REPORTING
+ enable_page_reporting();
+#endif
+
dm_device.state = DM_INITIALIZED;

dm_device.thread =
@@ -1731,6 +1818,9 @@ static int balloon_probe(struct hv_device *dev,
#ifdef CONFIG_MEMORY_HOTPLUG
unregister_memory_notifier(&hv_memory_nb);
restore_online_page_callback(&hv_online_page);
+#endif
+#ifdef CONFIG_PAGE_REPORTING
+ disable_page_reporting();
#endif
return ret;
}
@@ -1753,6 +1843,9 @@ static int balloon_remove(struct hv_device *dev)
#ifdef CONFIG_MEMORY_HOTPLUG
unregister_memory_notifier(&hv_memory_nb);
restore_online_page_callback(&hv_online_page);
+#endif
+#ifdef CONFIG_PAGE_REPORTING
+ disable_page_reporting();
#endif
spin_lock_irqsave(&dm_device.ha_lock, flags);
list_for_each_entry_safe(has, tmp, &dm->ha_region_list, list) {
diff --git a/include/asm-generic/hyperv-tlfs.h b/include/asm-generic/hyperv-tlfs.h
index e73a11850055..75c20be2cc44 100644
--- a/include/asm-generic/hyperv-tlfs.h
+++ b/include/asm-generic/hyperv-tlfs.h
@@ -89,6 +89,7 @@
#define HV_ACCESS_STATS BIT(8)
#define HV_DEBUGGING BIT(11)
#define HV_CPU_POWER_MANAGEMENT BIT(12)
+#define HV_ENABLE_EXTENDED_HYPERCALLS BIT(20)

/*
@@ -152,11 +153,18 @@ struct ms_hyperv_tsc_page {
#define HVCALL_FLUSH_GUEST_PHYSICAL_ADDRESS_SPACE 0x00af
#define HVCALL_FLUSH_GUEST_PHYSICAL_ADDRESS_LIST 0x00b0

+/* Extended hypercalls */
+#define HV_EXT_CALL_QUERY_CAPABILITIES 0x8001
+#define HV_EXT_CALL_MEMORY_HEAT_HINT 0x8003
+
#define HV_FLUSH_ALL_PROCESSORS BIT(0)
#define HV_FLUSH_ALL_VIRTUAL_ADDRESS_SPACES BIT(1)
#define HV_FLUSH_NON_GLOBAL_MAPPINGS_ONLY BIT(2)
#define HV_FLUSH_USE_EXTENDED_RANGE_FORMAT BIT(3)

+/* Extended capability bits */
+#define HV_EXT_CAPABILITY_MEMORY_COLD_DISCARD_HINT BIT(8)
+
enum HV_GENERIC_SET_FORMAT {
HV_GENERIC_SET_SPARSE_4K,
HV_GENERIC_SET_ALL,
@@ -367,7 +375,7 @@ struct hv_guest_mapping_flush {
*/
#define HV_MAX_FLUSH_PAGES (2048)

-/* HvFlushGuestPhysicalAddressList hypercall */
+/* HvFlushGuestPhysicalAddressList, HvExtCallMemoryHeatHint hypercall */
union hv_gpa_page_range {
u64 address_space;
struct {
@@ -375,6 +383,12 @@ union hv_gpa_page_range {
u64 largepage:1;
u64 basepfn:52;
} page;
+ struct {
+ u64 reserved:12;
+ u64 page_size:1;
+ u64 reserved1:8;
+ u64 base_large_pfn:43;
+ };
};

/*
@@ -494,4 +508,20 @@ struct hv_set_vp_registers_input {
} element[];
} __packed;

+/*
+ * The whole argument should fit in a page to be able to pass to the hypervisor
+ * in one hypercall.
+ */
+#define HV_MEMORY_HINT_MAX_GPA_PAGE_RANGES \
+ ((PAGE_SIZE - sizeof(struct hv_memory_hint)) / \
+ sizeof(union hv_gpa_page_range))
+
+/* HvExtCallMemoryHeatHint hypercall */
+#define HV_EXT_MEMORY_HEAT_HINT_TYPE_COLD_DISCARD 2
+struct hv_memory_hint {
+ u64 type:2;
+ u64 reserved:62;
+ union hv_gpa_page_range ranges[];
+} __packed;
+
#endif
diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
index c57799684170..93c1303f5e00 100644
--- a/include/asm-generic/mshyperv.h
+++ b/include/asm-generic/mshyperv.h
@@ -27,6 +27,7 @@

struct ms_hyperv_info {
u32 features;
+ u32 priv_high;
u32 misc_features;
u32 hints;
u32 nested_features;
@@ -170,6 +171,7 @@ void hyperv_report_panic_msg(phys_addr_t pa, size_t size);
bool hv_is_hyperv_initialized(void);
bool hv_is_hibernation_supported(void);
void hyperv_cleanup(void);
+bool hv_query_ext_cap(u64 cap_query);
#else /* CONFIG_HYPERV */
static inline bool hv_is_hyperv_initialized(void) { return false; }
static inline bool hv_is_hibernation_supported(void) { return false; }
--
2.17.1

Next message: Paul E. McKenney: "Re: [PATCH RFC x86/mce] Make mce_timed_out() identify holdout CPUs"
Previous message: Stephen Rothwell: "Re: linux-next: build warning after merge of the origin tree"
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