linux-kernel - [PATCH 03/10] KVM: x86/pmu: Squash period for checkpointed events based on host HLE/RTM

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Date: Fri,  5 Apr 2024 16:55:56 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Sandipan Das <sandipan.das@....com>, Jim Mattson <jmattson@...gle.com>, 
	Like Xu <like.xu.linux@...il.com>
Subject: [PATCH 03/10] KVM: x86/pmu: Squash period for checkpointed events
 based on host HLE/RTM

Zero out the sampling period for checkpointed events if the host supports
HLE or RTM, i.e. supports transactions and thus checkpointed events, not
based on whether the vCPU vendor model is Intel.  Perf's refusal to allow
a sample period for checkpointed events is based purely on whether or not
the CPU supports HLE/RTM transactions, i.e. perf has no knowledge of the
vCPU vendor model.

Note, it is _extremely_ unlikely that the existing code is a problem in
real world usage, as there are far, far bigger hurdles that would need to
be cleared to support cross-vendor vPMUs.  The motivation is mainly to
eliminate the use of guest_cpuid_is_intel(), in order to get to a state
where KVM pivots on AMD vs. Intel compatibility, i.e. doesn't check for
exactly vendor==Intel except in rare circumstances (i.e. for CPU quirks).

Cc: Like Xu <like.xu.linux@...il.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/pmu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
index c397b28e3d1b..8c3564917953 100644
--- a/arch/x86/kvm/pmu.c
+++ b/arch/x86/kvm/pmu.c
@@ -194,7 +194,7 @@ static int pmc_reprogram_counter(struct kvm_pmc *pmc, u32 type, u64 config,
 	attr.sample_period = get_sample_period(pmc, pmc->counter);

 	if ((attr.config & HSW_IN_TX_CHECKPOINTED) &&
-	    guest_cpuid_is_intel(pmc->vcpu)) {
+	    (boot_cpu_has(X86_FEATURE_RTM) || boot_cpu_has(X86_FEATURE_HLE))) {
 		/*
 		 * HSW_IN_TX_CHECKPOINTED is not supported with nonzero
 		 * period. Just clear the sample period so at least
-- 
2.44.0.478.gd926399ef9-goog