Messages in this thread | | | Date | Mon, 22 Feb 2021 08:24:51 -0800 | From | Sean Christopherson <> | Subject | Re: [PATCH v4 2/2] KVM: x86/mmu: Consider the hva in mmu_notifier retry |
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On Mon, Feb 22, 2021, David Stevens wrote: > --- > v3 -> v4: > - Skip prefetch while invalidations are in progress
Oof, nice catch.
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> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index 9ac0a727015d..f6aaac729667 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -2758,6 +2758,13 @@ static void direct_pte_prefetch(struct kvm_vcpu *vcpu, u64 *sptep) > if (sp->role.level > PG_LEVEL_4K) > return; > > + /* > + * If addresses are being invalidated, skip prefetching to avoid > + * accidentally prefetching those addresses. > + */ > + if (unlikely(vcpu->kvm->mmu_notifier_count)) > + return;
FNAME(pte_prefetch) needs the same check.
Paolo, this brings up a good addition for the work to integrate the mmu notifier into the rest of KVM, e.g. for vmcs12 pages. Ideally, gfn_to_page_many_atomic() and __gfn_to_pfn_memslot() would WARN if mmu_notifier_count is non-zero, but that will fire all over the place until the nested code properly integrates the notifier. There are a few use cases where racing with the notifier is acceptable, e.g. reexecute_instruction(), but hopefully we can address those flows without things getting too ugly.
> + > __direct_pte_prefetch(vcpu, sp, sptep); > }
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