linux-kernel - [tip: x86/urgent] x86/resctrl: Fix memory bandwidth counter width for Hygon

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Message-ID: <176832083920.510.6826832603557460892.tip-bot2@tip-bot2>
Date: Tue, 13 Jan 2026 16:13:59 -0000
From: "tip-bot2 for Xiaochen Shen" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Xiaochen Shen <shenxiaochen@...n-hieco.net>,
 "Borislav Petkov (AMD)" <bp@...en8.de>, Tony Luck <tony.luck@...el.com>,
 Reinette Chatre <reinette.chatre@...el.com>, stable@...r.kernel.org,
 x86@...nel.org, linux-kernel@...r.kernel.org
Subject:
 [tip: x86/urgent] x86/resctrl: Fix memory bandwidth counter width for Hygon

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     7517e899e1b87b4c22a92c7e40d8733c48e4ec3c
Gitweb:        https://git.kernel.org/tip/7517e899e1b87b4c22a92c7e40d8733c48e4ec3c
Author:        Xiaochen Shen <shenxiaochen@...n-hieco.net>
AuthorDate:    Tue, 09 Dec 2025 14:26:50 +08:00
Committer:     Borislav Petkov (AMD) <bp@...en8.de>
CommitterDate: Tue, 13 Jan 2026 16:44:26 +01:00

x86/resctrl: Fix memory bandwidth counter width for Hygon

The memory bandwidth calculation relies on reading the hardware counter
and measuring the delta between samples. To ensure accurate measurement,
the software reads the counter frequently enough to prevent it from
rolling over twice between reads.

The default Memory Bandwidth Monitoring (MBM) counter width is 24 bits.
Hygon CPUs provide a 32-bit width counter, but they do not support the
MBM capability CPUID leaf (0xF.[ECX=1]:EAX) to report the width offset
(from 24 bits).

Consequently, the kernel falls back to the 24-bit default counter width,
which causes incorrect overflow handling on Hygon CPUs.

Fix this by explicitly setting the counter width offset to 8 bits (resulting
in a 32-bit total counter width) for Hygon CPUs.

Fixes: d8df126349da ("x86/cpu/hygon: Add missing resctrl_cpu_detect() in bsp_init helper")
Signed-off-by: Xiaochen Shen <shenxiaochen@...n-hieco.net>
Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
Reviewed-by: Tony Luck <tony.luck@...el.com>
Reviewed-by: Reinette Chatre <reinette.chatre@...el.com>
Cc: stable@...r.kernel.org
Link: https://patch.msgid.link/20251209062650.1536952-3-shenxiaochen@open-hieco.net
---
 arch/x86/kernel/cpu/resctrl/core.c     | 15 +++++++++++++--
 arch/x86/kernel/cpu/resctrl/internal.h |  3 +++
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index 10de159..6ebff44 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -1021,8 +1021,19 @@ void resctrl_cpu_detect(struct cpuinfo_x86 *c)
 		c->x86_cache_occ_scale = ebx;
 		c->x86_cache_mbm_width_offset = eax & 0xff;
 
-		if (c->x86_vendor == X86_VENDOR_AMD && !c->x86_cache_mbm_width_offset)
-			c->x86_cache_mbm_width_offset = MBM_CNTR_WIDTH_OFFSET_AMD;
+		if (!c->x86_cache_mbm_width_offset) {
+			switch (c->x86_vendor) {
+			case X86_VENDOR_AMD:
+				c->x86_cache_mbm_width_offset = MBM_CNTR_WIDTH_OFFSET_AMD;
+				break;
+			case X86_VENDOR_HYGON:
+				c->x86_cache_mbm_width_offset = MBM_CNTR_WIDTH_OFFSET_HYGON;
+				break;
+			default:
+				/* Leave c->x86_cache_mbm_width_offset as 0 */
+				break;
+			}
+		}
 	}
 }
 
diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index 4a916c8..79c1865 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -14,6 +14,9 @@
 
 #define MBM_CNTR_WIDTH_OFFSET_AMD	20
 
+/* Hygon MBM counter width as an offset from MBM_CNTR_WIDTH_BASE */
+#define MBM_CNTR_WIDTH_OFFSET_HYGON	8
+
 #define RMID_VAL_ERROR			BIT_ULL(63)
 
 #define RMID_VAL_UNAVAIL		BIT_ULL(62)