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SubjectRe: [PATCH] KVM: x86/mmu: Skip !MMU-present SPTEs when removing SP in exclusive mode
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On 10/03/21 01:30, Sean Christopherson wrote:
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index 50ef757c5586..f0c99fa04ef2 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -323,7 +323,18 @@ static void handle_removed_tdp_mmu_page(struct kvm *kvm, u64 *pt,
> cpu_relax();
> }
> } else {
> + /*
> + * If the SPTE is not MMU-present, there is no backing
> + * page associated with the SPTE and so no side effects
> + * that need to be recorded, and exclusive ownership of
> + * mmu_lock ensures the SPTE can't be made present.
> + * Note, zapping MMIO SPTEs is also unnecessary as they
> + * are guarded by the memslots generation, not by being
> + * unreachable.
> + */
> old_child_spte = READ_ONCE(*sptep);
> + if (!is_shadow_present_pte(old_child_spte))
> + continue;
>
> /*
> * Marking the SPTE as a removed SPTE is not

Ben, do you plan to make this path take mmu_lock for read? If so, this
wouldn't be too useful IIUC.

Paolo

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