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KVM: x86: Ensure a full memory barrier is emitted in the VM-Exit path
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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@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
[sean: massage changelog]
Tested-by: Xiangfei Ma <xiangfeix.ma@intel.com>
Tested-by: Yongwei Ma <yongwei.ma@intel.com>
Link: https://lore.kernel.org/r/20240309010929.1403984-5-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
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Yan Zhao authored and Sean Christopherson committed Jun 7, 2024
1 parent f05eda1 commit 65a4de0
Showing 1 changed file with 6 additions and 0 deletions.
6 changes: 6 additions & 0 deletions arch/x86/kvm/x86.c
Original file line number Diff line number Diff line change
Expand Up @@ -11135,6 +11135,12 @@ 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:
*/
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