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Message-Id: <20201124205245.4164633-2-fenghua.yu@intel.com>
Date: Tue, 24 Nov 2020 20:52:42 +0000
From: Fenghua Yu <fenghua.yu@...el.com>
To: "Thomas Gleixner" <tglx@...utronix.de>,
"Borislav Petkov" <bp@...en8.de>, "Ingo Molnar" <mingo@...hat.com>,
"Peter Zijlstra" <peterz@...radead.org>,
"Tony Luck" <tony.luck@...el.com>,
"Randy Dunlap" <rdunlap@...radead.org>,
"Xiaoyao Li " <xiaoyao.li@...el.com>,
"Ravi V Shankar" <ravi.v.shankar@...el.com>
Cc: "linux-kernel" <linux-kernel@...r.kernel.org>,
"x86" <x86@...nel.org>, Fenghua Yu <fenghua.yu@...el.com>
Subject: [PATCH v4 1/4] x86/cpufeatures: Enumerate #DB for bus lock detection
A bus lock is acquired though either split locked access to
writeback (WB) memory or any locked access to non-WB memory. This is
typically >1000 cycles slower than an atomic operation within a cache
line. It also disrupts performance on other cores.
Some CPUs have ability to notify the kernel by an #DB trap after a user
instruction acquires a bus lock and is executed. This allows the kernel
to enforce user application throttling or mitigations.
The CPU feature flag to be shown in /proc/cpuinfo will be "bus_lock_detect".
Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
Reviewed-by: Tony Luck <tony.luck@...el.com>
---
arch/x86/include/asm/cpufeatures.h | 1 +
1 file changed, 1 insertion(+)
diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index dad350d42ecf..f375d9cb8123 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -352,6 +352,7 @@
#define X86_FEATURE_AVX512_VPOPCNTDQ (16*32+14) /* POPCNT for vectors of DW/QW */
#define X86_FEATURE_LA57 (16*32+16) /* 5-level page tables */
#define X86_FEATURE_RDPID (16*32+22) /* RDPID instruction */
+#define X86_FEATURE_BUS_LOCK_DETECT (16*32+24) /* Bus Lock detect */
#define X86_FEATURE_CLDEMOTE (16*32+25) /* CLDEMOTE instruction */
#define X86_FEATURE_MOVDIRI (16*32+27) /* MOVDIRI instruction */
#define X86_FEATURE_MOVDIR64B (16*32+28) /* MOVDIR64B instruction */
--
2.29.2
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