linux-kernel - [PATCH 5.10 15/36] perf/x86/kvm: Fix Broadwell Xeon stepping in isolation

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Date:   Mon, 26 Apr 2021 09:29:57 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Jim Mattson <jmattson@...gle.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Peter Shier <pshier@...gle.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.10 15/36] perf/x86/kvm: Fix Broadwell Xeon stepping in isolation_ucodes[]

From: Jim Mattson <jmattson@...gle.com>

[ Upstream commit 4b2f1e59229b9da319d358828cdfa4ddbc140769 ]

The only stepping of Broadwell Xeon parts is stepping 1. Fix the
relevant isolation_ucodes[] entry, which previously enumerated
stepping 2.

Although the original commit was characterized as an optimization, it
is also a workaround for a correctness issue.

If a PMI arrives between kvm's call to perf_guest_get_msrs() and the
subsequent VM-entry, a stale value for the IA32_PEBS_ENABLE MSR may be
restored at the next VM-exit. This is because, unbeknownst to kvm, PMI
throttling may clear bits in the IA32_PEBS_ENABLE MSR. CPUs with "PEBS
isolation" don't suffer from this issue, because perf_guest_get_msrs()
doesn't report the IA32_PEBS_ENABLE value.

Fixes: 9b545c04abd4f ("perf/x86/kvm: Avoid unnecessary work in guest filtering")
Signed-off-by: Jim Mattson <jmattson@...gle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Peter Shier <pshier@...gle.com>
Acked-by: Andi Kleen <ak@...ux.intel.com>
Link: https://lkml.kernel.org/r/20210422001834.1748319-1-jmattson@google.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/x86/events/intel/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index e7dc13fe5e29..0b9975200ae3 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -4387,7 +4387,7 @@ static const struct x86_cpu_desc isolation_ucodes[] = {
 	INTEL_CPU_DESC(INTEL_FAM6_BROADWELL_D,		 3, 0x07000009),
 	INTEL_CPU_DESC(INTEL_FAM6_BROADWELL_D,		 4, 0x0f000009),
 	INTEL_CPU_DESC(INTEL_FAM6_BROADWELL_D,		 5, 0x0e000002),
-	INTEL_CPU_DESC(INTEL_FAM6_BROADWELL_X,		 2, 0x0b000014),
+	INTEL_CPU_DESC(INTEL_FAM6_BROADWELL_X,		 1, 0x0b000014),
 	INTEL_CPU_DESC(INTEL_FAM6_SKYLAKE_X,		 3, 0x00000021),
 	INTEL_CPU_DESC(INTEL_FAM6_SKYLAKE_X,		 4, 0x00000000),
 	INTEL_CPU_DESC(INTEL_FAM6_SKYLAKE_X,		 5, 0x00000000),
-- 
2.30.2