linux-kernel - [PATCH] x86/perf: Fix guest_get_msrs static call if there is no PMU

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Message-Id: <20210305223331.4173565-1-seanjc@google.com>
Date:   Fri,  5 Mar 2021 14:33:31 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, x86@...nel.org
Cc:     Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        Like Xu <like.xu@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>, kvm@...r.kernel.org,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: [PATCH] x86/perf: Fix guest_get_msrs static call if there is no PMU

Handle a NULL x86_pmu.guest_get_msrs at invocation instead of patching
in perf_guest_get_msrs_nop() during setup.  If there is no PMU, setup
bails before updating the static calls, leaving x86_pmu.guest_get_msrs
NULL and thus a complete nop.  Ultimately, this causes VMX abort on
VM-Exit due to KVM putting random garbage from the stack into the MSR
load list.

Fixes: abd562df94d1 ("x86/perf: Use static_call for x86_pmu.guest_get_msrs")
Cc: Like Xu <like.xu@...ux.intel.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Jim Mattson <jmattson@...gle.com>
Cc: kvm@...r.kernel.org
Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/events/core.c | 16 +++++-----------
 1 file changed, 5 insertions(+), 11 deletions(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 6ddeed3cd2ac..ff874461f14c 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -671,7 +671,11 @@ void x86_pmu_disable_all(void)
 
 struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr)
 {
-	return static_call(x86_pmu_guest_get_msrs)(nr);
+	if (x86_pmu.guest_get_msrs)
+		return static_call(x86_pmu_guest_get_msrs)(nr);
+
+	*nr = 0;
+	return NULL;
 }
 EXPORT_SYMBOL_GPL(perf_guest_get_msrs);
 
@@ -1944,13 +1948,6 @@ static void _x86_pmu_read(struct perf_event *event)
 	x86_perf_event_update(event);
 }
 
-static inline struct perf_guest_switch_msr *
-perf_guest_get_msrs_nop(int *nr)
-{
-	*nr = 0;
-	return NULL;
-}
-
 static int __init init_hw_perf_events(void)
 {
 	struct x86_pmu_quirk *quirk;
@@ -2024,9 +2021,6 @@ static int __init init_hw_perf_events(void)
 	if (!x86_pmu.read)
 		x86_pmu.read = _x86_pmu_read;
 
-	if (!x86_pmu.guest_get_msrs)
-		x86_pmu.guest_get_msrs = perf_guest_get_msrs_nop;
-
 	x86_pmu_static_call_update();
 
 	/*
-- 
2.30.1.766.gb4fecdf3b7-goog