On 3/9/24 02:09, Sean Christopherson wrote:
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().
Do you really need mfence or is a locked operation enough? mfence is mb(), not smp_mb().
Paolo
+ /* + * 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();
