Messages in this thread |  | | Date | Thu, 21 Oct 2021 19:44:40 +0200 | Subject | Re: [PATCH 3/4] KVM: X86: Use smp_rmb() to pair with smp_wmb() in mmu_try_to_unsync_pages() | From | Paolo Bonzini <> |
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On 19/10/21 13:01, Lai Jiangshan wrote: > From: Lai Jiangshan<laijs@linux.alibaba.com> > > The commit 578e1c4db2213 ("kvm: x86: Avoid taking MMU lock in > kvm_mmu_sync_roots if no sync is needed") added smp_wmb() in > mmu_try_to_unsync_pages(), but the corresponding smp_load_acquire() > isn't used on the load of SPTE.W which is impossible since the load of > SPTE.W is performed in the CPU's pagetable walking. > > This patch changes to use smp_rmb() instead. This patch fixes nothing > but just comments since smp_rmb() is NOP and compiler barrier() is not > required since the load of SPTE.W is before VMEXIT.
I think that even implicit loads during pagetable walking obey read-read ordering on x86, but this is clearer and it is necessary for patch 4.
Paolo
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