linux-kernel - [PATCH] KVM: X86: correct trace_kvm_pv_tlb

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Message-Id: <20220504182707.680-1-jon@nutanix.com>
Date:   Wed,  4 May 2022 14:27:07 -0400
From:   Jon Kohler <jon@...anix.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Jon Kohler <jon@...anix.com>
Subject: [PATCH] KVM: X86: correct trace_kvm_pv_tlb_flush stats

The trace point in record_steal_time() is above the conditional
that fires kvm_vcpu_flush_tlb_guest(), so even when we might
not be flushing tlb, we still record that we are.

Fix by nestling trace_kvm_pv_tlb_flush() under appropriate
conditional. This results in the stats for kvm:kvm_pv_tlb_flush,
as trivially observable by perf stat -e "kvm:*" -a sleep Xs, in
reporting the amount of times we actually do a pv tlb flush,
instead of just the amount of times we happen to call
record_steal_time().

Signed-off-by: Jon Kohler <jon@...anix.com>
---
 arch/x86/kvm/x86.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 4790f0d7d40b..8d4e0e58ec34 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3410,9 +3410,9 @@ static void record_steal_time(struct kvm_vcpu *vcpu)
 
 		vcpu->arch.st.preempted = 0;
 
-		trace_kvm_pv_tlb_flush(vcpu->vcpu_id,
-				       st_preempted & KVM_VCPU_FLUSH_TLB);
 		if (st_preempted & KVM_VCPU_FLUSH_TLB)
+			trace_kvm_pv_tlb_flush(vcpu->vcpu_id,
+				st_preempted & KVM_VCPU_FLUSH_TLB);
 			kvm_vcpu_flush_tlb_guest(vcpu);
 
 		if (!user_access_begin(st, sizeof(*st)))
-- 
2.30.1 (Apple Git-130)