linux-kernel - [PATCH v4 28/38] KVM: x86/pmu/svm: Set GuestOnly bit and clear HostOnly bit when guest writes to event selectors

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Message-ID: <20250324173121.1275209-29-mizhang@google.com>
Date: Mon, 24 Mar 2025 17:31:08 +0000
From: Mingwei Zhang <mizhang@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, Liang@...gle.com, 
	Kan <kan.liang@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>, 
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org, 
	kvm@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	Mingwei Zhang <mizhang@...gle.com>, Yongwei Ma <yongwei.ma@...el.com>, 
	Xiong Zhang <xiong.y.zhang@...ux.intel.com>, Dapeng Mi <dapeng1.mi@...ux.intel.com>, 
	Jim Mattson <jmattson@...gle.com>, Sandipan Das <sandipan.das@....com>, 
	Zide Chen <zide.chen@...el.com>, Eranian Stephane <eranian@...gle.com>, 
	Das Sandipan <Sandipan.Das@....com>, Shukla Manali <Manali.Shukla@....com>, 
	Nikunj Dadhania <nikunj.dadhania@....com>
Subject: [PATCH v4 28/38] KVM: x86/pmu/svm: Set GuestOnly bit and clear
 HostOnly bit when guest writes to event selectors

From: Sandipan Das <sandipan.das@....com>

On AMD platforms, there is no way to restore PerfCntrGlobalCtl at
VM-Entry or clear it at VM-Exit. Since the register states will be
restored before entering and saved after exiting guest context, the
counters can keep ticking and even overflow leading to chaos while
still in host context.

To avoid this, intecept event selectors, which is already done by mediated
PMU. In addition, always set the GuestOnly bit and clear the HostOnly bit
for PMU selectors on AMD. Doing so allows the counters run only in guest
context even if their enable bits are still set after VM exit and before
host/guest PMU context switch.

Signed-off-by: Sandipan Das <sandipan.das@....com>
Signed-off-by: Mingwei Zhang <mizhang@...gle.com>
---
 arch/x86/kvm/svm/pmu.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm/pmu.c b/arch/x86/kvm/svm/pmu.c
index 9feaca739b96..1a7e3a897fdf 100644
--- a/arch/x86/kvm/svm/pmu.c
+++ b/arch/x86/kvm/svm/pmu.c
@@ -165,7 +165,8 @@ static int amd_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		data &= ~pmu->reserved_bits;
 		if (data != pmc->eventsel) {
 			pmc->eventsel = data;
-			pmc->eventsel_hw = data;
+			pmc->eventsel_hw = (data & ~AMD64_EVENTSEL_HOSTONLY) |
+					   AMD64_EVENTSEL_GUESTONLY;
 			kvm_pmu_request_counter_reprogram(pmc);
 		}
 		return 0;
-- 
2.49.0.395.g12beb8f557-goog