From f068dd9e5f4dd6ec67b96ddeb58f84027b5ec0a7 Mon Sep 17 00:00:00 2001 From: Wanpeng Li Date: Tue, 18 May 2021 05:00:33 -0700 Subject: [PATCH] KVM: X86: Fix vCPU preempted state from guest's point of view Commit ffe79f85161f (kvm: x86: only provide PV features if enabled in guest's CPUID) avoids to access pv tlb shootdown host side logic when this pv feature is not exposed to guest, however, kvm_steal_time.preempted not only leveraged by pv tlb shootdown logic but also mitigate the lock holder preemption issue. From guest's point of view, vCPU is always preempted since we lose the reset of kvm_steal_time.preempted before vmentry if pv tlb shootdown feature is not exposed. This patch fixes it by clearing kvm_steal_time.preempted before vmentry. Fixes: ffe79f85161f (kvm: x86: only provide PV features if enabled in guest's CPUID) Reviewed-by: Sean Christopherson Cc: stable@vger.kernel.org Signed-off-by: Wanpeng Li Message-Id: <1621339235-11131-3-git-send-email-wanpengli@tencent.com> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/x86.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index dfb7c320581fc..bed7b5348c0e9 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -3105,6 +3105,8 @@ static void record_steal_time(struct kvm_vcpu *vcpu) st->preempted & KVM_VCPU_FLUSH_TLB); if (xchg(&st->preempted, 0) & KVM_VCPU_FLUSH_TLB) kvm_vcpu_flush_tlb_guest(vcpu); + } else { + st->preempted = 0; } vcpu->arch.st.preempted = 0; -- 2.39.5