Re: [PATCH v3 08/28] KVM: x86/mmu: Batch TLB flushes from TDP MMU for MMU notifier change_spte

Mingwei Zhang
2022-03-03T18:08:55Z

On Sat, Feb 26, 2022, Sean Christopherson wrote:
> Batch TLB flushes (with other MMUs) when handling ->change_spte()
> notifications in the TDP MMU. The MMU notifier path in question doesn't
> allow yielding and correcty flushes before dropping mmu_lock.
nit: correctly
>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> Reviewed-by: Ben Gardon <bgardon@google.com>
Reviewed-by: Mingwei Zhang <mizhang@google.com>
> ---
> arch/x86/kvm/mmu/tdp_mmu.c | 13 ++++++-------
> 1 file changed, 6 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index 848448b65703..634a2838e117 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -1203,13 +1203,12 @@ static bool set_spte_gfn(struct kvm *kvm, struct tdp_iter *iter,
> */
> bool kvm_tdp_mmu_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
> {
> - bool flush = kvm_tdp_mmu_handle_gfn(kvm, range, set_spte_gfn);
> -
> - /* FIXME: return 'flush' instead of flushing here. */
> - if (flush)
> - kvm_flush_remote_tlbs_with_address(kvm, range->start, 1);
> -
> - return false;
> + /*
> + * No need to handle the remote TLB flush under RCU protection, the
> + * target SPTE _must_ be a leaf SPTE, i.e. cannot result in freeing a
> + * shadow page. See the WARN on pfn_changed in __handle_changed_spte().
> + */
> + return kvm_tdp_mmu_handle_gfn(kvm, range, set_spte_gfn);
> }
>
> /*
> --
> 2.35.1.574.g5d30c73bfb-goog
>