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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <20210422001834.1748319-1-jmattson@google.com>
Date:   Wed, 21 Apr 2021 17:18:34 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>, linux-kernel@...r.kernel.org,
        kvm-list@...r.kernel.org
Cc:     Jim Mattson <jmattson@...gle.com>, Peter Shier <pshier@...gle.com>
Subject: [PATCH] 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")
Cc: Andi Kleen <ak@...ux.intel.com>
Reported-by: Peter Shier <pshier@...gle.com>
Signed-off-by: Jim Mattson <jmattson@...gle.com>
Reviewed-by: Peter Shier <pshier@...gle.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 37ce38403cb8..c57ec8e27907 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),
-- 
2.31.1.368.gbe11c130af-goog