From: Yan Zhao <yan.y.zhao@xxxxxxxxx> Ensure a full memory barrier is emitted in the VM-Exit path, as a full barrier is required on Intel CPUs to evict WC buffers. This will allow unconditionally honoring guest PAT on Intel CPUs that support self-snoop. As srcu_read_lock() is always called in the VM-Exit path and it internally has a smp_mb(), call smp_mb__after_srcu_read_lock() to avoid adding a second fence and make sure smp_mb() is called without dependency on implementation details of srcu_read_lock(). Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> Cc: Sean Christopherson <seanjc@xxxxxxxxxx> Cc: Kevin Tian <kevin.tian@xxxxxxxxx> Signed-off-by: Yan Zhao <yan.y.zhao@xxxxxxxxx> [sean: massage changelog] Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> --- arch/x86/kvm/x86.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 276ae56dd888..69e815df1699 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -11082,6 +11082,12 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) kvm_vcpu_srcu_read_lock(vcpu); + /* + * Call this to ensure WC buffers in guest are evicted after each VM + * Exit, so that the evicted WC writes can be snooped across all cpus + */ + smp_mb__after_srcu_read_lock(); + /* * Profile KVM exit RIPs: */ -- 2.44.0.278.ge034bb2e1d-goog
