KVM: X86: Fix vCPU preempted state from guest's point of view

Commit 66570e966dd9 (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: 66570e966dd9 (kvm: x86: only provide PV features if enabled in guest's CPUID)
Reviewed-by: Sean Christopherson <seanjc@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Message-Id: <1621339235-11131-3-git-send-email-wanpengli@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index dfb7c320581fcbed892fd45e45a82ed5a416a6d0..bed7b5348c0e90494decca271abf6916a7697b96 100644 (file)
--- 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;