[RFC PATCH 18/31] x86/resctrl: Introduce memory region based MBM read callback on MMIO space
From: Chen Yu
Date: Sun Aug 02 2026 - 12:17:29 EST
Enhance erdt_mon_read() to support region-based memory bandwidth reads,
and implement the low-level MMIO-based region-aware
erdt_read_region_mbm() to deal with region-aware MBM.
Signed-off-by: Chen Yu <yu.c.chen@xxxxxxxxx>
---
arch/x86/kernel/cpu/resctrl/erdt.c | 102 +++++++++++++++++++++++++
arch/x86/kernel/cpu/resctrl/internal.h | 4 +
arch/x86/kernel/cpu/resctrl/monitor.c | 8 +-
include/linux/resctrl_types.h | 5 ++
4 files changed, 115 insertions(+), 4 deletions(-)
diff --git a/arch/x86/kernel/cpu/resctrl/erdt.c b/arch/x86/kernel/cpu/resctrl/erdt.c
index a14de9eb8b88..35217f48b3d9 100644
--- a/arch/x86/kernel/cpu/resctrl/erdt.c
+++ b/arch/x86/kernel/cpu/resctrl/erdt.c
@@ -30,6 +30,8 @@ static bool erdt_enabled;
/* Set in a monitoring counter when it holds no valid data to report. */
#define UNAVAILABLE_COUNTER BIT_ULL(63)
#define CMRC_FLAG_UNAVAILABLE_BIT BIT(0)
+#define MMRC_FLAG_UNAVAILABLE_BIT BIT(0)
+#define FIXPOINT_LOW_BITS 16
/* Bitmask of valid sub-tables found in the first RMDD, used to ensure all RMDDs match. */
static u32 valid_subtbl_mask;
@@ -96,6 +98,103 @@ static int erdt_read_l3_occupancy(const struct erdt_domain_info *d, u32 rmid, u6
return 0;
}
+static void __iomem *mmrc_index_function_1(const struct erdt_domain_info *d,
+ struct acpi_erdt_mmrc *mmrc,
+ int rmid, int region_idx)
+{
+ u64 blk_rmid, blk_offset;
+ void __iomem *vaddr;
+
+ /*
+ * Block_to_locate_RMID# = floor((RMID# % 32) / 8) x 4 x 4096B;
+ * Offset_within_this_Block = (floor(((RMID#/32)x8)+RMID#%8) x
+ * 8B)+(Region# x 2048B);
+ * MMIO_ADDRESS_for_RMID#_Region# =
+ * MBM Register Block Base Address + Block_to_locate_RMID# +
+ * Offset_within_this_Block;
+ */
+ blk_rmid = ((rmid % 32) / 8) * 4 * 4096;
+ blk_offset = ((rmid / 32) * 8 + (rmid % 8)) * 8 + region_idx * 2048;
+ vaddr = d->base[ERDT_MMIO_MMRC_BASE] + blk_rmid + blk_offset;
+
+ return vaddr;
+}
+
+static u64 apply_correction_factor(u64 val, u32 factor)
+{
+ if (!factor)
+ return val;
+
+ return ((val * factor) >> FIXPOINT_LOW_BITS);
+}
+
+static int erdt_read_region_mbm(struct rdt_domain_hdr *hdr,
+ const struct erdt_domain_info *d, int rmid,
+ int eventid, u64 *val)
+{
+ int region_idx = eventid - QOS_L3_MBM_R0_EVENT_ID;
+ int corr_factor_len, corr_factor = 0;
+ struct rdt_hw_l3_mon_domain *hw_dom;
+ u64 mbm_rmid_count = 0, chunks = 0;
+ struct acpi_erdt_mmrc *mmrc = NULL;
+ struct rdt_l3_mon_domain *mon_dom;
+ struct arch_mbm_state *am;
+ void __iomem *vaddr;
+
+ mmrc = d->mmrc;
+ if (!mmrc)
+ return -EIO;
+
+ if (!domain_header_is_valid(hdr, RESCTRL_MON_DOMAIN, RDT_RESOURCE_L3))
+ return -EIO;
+
+ mon_dom = container_of(hdr, struct rdt_l3_mon_domain, hdr);
+ hw_dom = resctrl_to_arch_mon_dom(mon_dom);
+
+ vaddr = mmrc_index_function_1(d, mmrc, rmid, region_idx);
+ mbm_rmid_count = readq(vaddr);
+
+ /*
+ * Bit 63 only reports whether the data is unavailable on domains that
+ * advertise support for it. Where it is not supported the bit is part
+ * of the counter and must not be interpreted as a status flag.
+ */
+ if ((mmrc->flags & MMRC_FLAG_UNAVAILABLE_BIT) &&
+ (mbm_rmid_count & UNAVAILABLE_COUNTER))
+ return -EINVAL;
+
+ corr_factor_len = mmrc->corr_factor_list_len;
+ if (corr_factor_len) {
+ /*
+ * 0: Do not apply a correction factor to
+ * the MBM values.
+ * 1: Apply a single correction factor.
+ * Max RMID+1: Apply the indicated indexed
+ * correction factor to the corresponding
+ * RMID value for MBM counter.
+ */
+ if (corr_factor_len == 1)
+ corr_factor = mmrc->corr_factor_list[0];
+ else if (rmid < corr_factor_len)
+ corr_factor = mmrc->corr_factor_list[rmid];
+ else
+ return -EINVAL;
+ }
+
+ am = get_arch_mbm_state(hw_dom, rmid, eventid);
+ if (am) {
+ am->chunks += mbm_overflow_count(am->prev_mon_val, mbm_rmid_count,
+ mmrc->counter_width);
+
+ chunks = apply_correction_factor(am->chunks, corr_factor);
+ am->prev_mon_val = mbm_rmid_count;
+ }
+
+ *val = chunks * mmrc->up_scale;
+
+ return 0;
+}
+
int erdt_mon_read(struct rdt_domain_hdr *hdr, enum resctrl_event_id evtid, u32 rmid, u64 *val)
{
struct rdt_hw_l3_mon_domain *hw_dom;
@@ -109,6 +208,9 @@ int erdt_mon_read(struct rdt_domain_hdr *hdr, enum resctrl_event_id evtid, u32 r
if (evtid == QOS_L3_OCCUP_EVENT_ID)
return erdt_read_l3_occupancy(d, rmid, val);
+ if (rmbm_event(evtid))
+ return erdt_read_region_mbm(hdr, d, rmid, evtid, val);
+
return -EIO;
}
diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index c337c4336789..b665b19b6f8b 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -320,4 +320,8 @@ int erdt_mon_read(struct rdt_domain_hdr *hdr, enum resctrl_event_id evtid, u32 r
int erdt_init(void);
void erdt_exit(void);
+u64 mbm_overflow_count(u64 prev_val, u64 cur_val, unsigned int width);
+struct arch_mbm_state *get_arch_mbm_state(struct rdt_hw_l3_mon_domain *hw_dom,
+ u32 rmid,
+ enum resctrl_event_id eventid);
#endif /* _ASM_X86_RESCTRL_INTERNAL_H */
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index ac5353fd0efd..c60d3d55a96c 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -157,9 +157,9 @@ static int __rmid_read_phys(u32 prmid, enum resctrl_event_id eventid, u64 *val)
return 0;
}
-static struct arch_mbm_state *get_arch_mbm_state(struct rdt_hw_l3_mon_domain *hw_dom,
- u32 rmid,
- enum resctrl_event_id eventid)
+struct arch_mbm_state *get_arch_mbm_state(struct rdt_hw_l3_mon_domain *hw_dom,
+ u32 rmid,
+ enum resctrl_event_id eventid)
{
struct arch_mbm_state *state;
@@ -209,7 +209,7 @@ void resctrl_arch_reset_rmid_all(struct rdt_resource *r, struct rdt_l3_mon_domai
}
}
-static u64 mbm_overflow_count(u64 prev_val, u64 cur_val, unsigned int width)
+u64 mbm_overflow_count(u64 prev_val, u64 cur_val, unsigned int width)
{
u64 shift = 64 - width, chunks;
diff --git a/include/linux/resctrl_types.h b/include/linux/resctrl_types.h
index 41dc1dff8c16..ee8fc7df22f9 100644
--- a/include/linux/resctrl_types.h
+++ b/include/linux/resctrl_types.h
@@ -77,6 +77,11 @@ enum resctrl_event_id {
QOS_NUM_EVENTS,
};
+static inline bool rmbm_event(unsigned int e)
+{
+ return (e >= QOS_L3_MBM_R0_EVENT_ID) && (e <= QOS_L3_MBM_R3_EVENT_ID);
+}
+
#define QOS_NUM_L3_MBM_EVENTS (QOS_L3_MBM_R3_EVENT_ID - QOS_L3_MBM_TOTAL_EVENT_ID + 1)
#define MBM_STATE_IDX(evt) ((evt) - QOS_L3_MBM_TOTAL_EVENT_ID)
--
2.43.0