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From: "tip-bot2 for Jim Mattson" <tip-bot2@linutronix.de>
To: linux-tip-commits@vger.kernel.org
Cc: Jim Mattson <jmattson@google.com>,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>,
	Peter Shier <pshier@google.com>, Andi Kleen <ak@linux.intel.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org
Subject: [tip: perf/urgent] perf/x86/kvm: Fix Broadwell Xeon stepping in isolation_ucodes[]
Date: Fri, 23 Apr 2021 06:53:01 -0000	[thread overview]
Message-ID: <161916078180.29796.11319206773894740858.tip-bot2@tip-bot2> (raw)
In-Reply-To: <20210422001834.1748319-1-jmattson@google.com>

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

Commit-ID:     4b2f1e59229b9da319d358828cdfa4ddbc140769
Gitweb:        https://git.kernel.org/tip/4b2f1e59229b9da319d358828cdfa4ddbc140769
Author:        Jim Mattson <jmattson@google.com>
AuthorDate:    Wed, 21 Apr 2021 17:18:34 -07:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Thu, 22 Apr 2021 14:36:01 +02:00

perf/x86/kvm: Fix Broadwell Xeon stepping in isolation_ucodes[]

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@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Peter Shier <pshier@google.com>
Acked-by: Andi Kleen <ak@linux.intel.com>
Link: https://lkml.kernel.org/r/20210422001834.1748319-1-jmattson@google.com
---
 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 37ce384..c57ec8e 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -4516,7 +4516,7 @@ 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),

      parent reply	other threads:[~2021-04-23  6:53 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-22  0:18 [PATCH] perf/x86/kvm: Fix Broadwell Xeon stepping in isolation_ucodes[] Jim Mattson
2021-04-22  2:05 ` Andi Kleen
2021-04-23  6:53 ` tip-bot2 for Jim Mattson [this message]

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