From: Wanpeng Li wanpengli@tencent.com
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 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) Cc: stable@vger.kernel.org Signed-off-by: Wanpeng Li wanpengli@tencent.com --- arch/x86/kvm/x86.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index c0244a6..c38e990 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -3105,7 +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;
On Sat, May 08, 2021, Wanpeng Li wrote:
From: Wanpeng Li wanpengli@tencent.com
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 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) Cc: stable@vger.kernel.org Signed-off-by: Wanpeng Li wanpengli@tencent.com
arch/x86/kvm/x86.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index c0244a6..c38e990 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -3105,7 +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;
Curly braces needed since the if-statment needs 'em. Other than that,
Reviewed-by: Sean Christopherson seanjc@google.com
vcpu->arch.st.preempted = 0; -- 2.7.4
On Tue, 11 May 2021 at 08:18, Sean Christopherson seanjc@google.com wrote:
On Sat, May 08, 2021, Wanpeng Li wrote:
From: Wanpeng Li wanpengli@tencent.com
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 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) Cc: stable@vger.kernel.org Signed-off-by: Wanpeng Li wanpengli@tencent.com
arch/x86/kvm/x86.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index c0244a6..c38e990 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -3105,7 +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);
}
} elsest->preempted = 0;Curly braces needed since the if-statment needs 'em. Other than that,
Will send out a new version after 1-2 get reviewed. :)
Reviewed-by: Sean Christopherson seanjc@google.com
vcpu->arch.st.preempted = 0;-- 2.7.4
linux-stable-mirror@lists.linaro.org
-
Sean Christopherson -
Wanpeng Li