From: Sean Christopherson <seanjc@google.com>
To: Junaid Shahid <junaids@google.com>
Cc: kvm@vger.kernel.org, pbonzini@redhat.com, jmattson@google.com,
bgardon@google.com
Subject: Re: [PATCH] kvm: mmu: Use fast PF path for access tracking of huge pages when possible
Date: Wed, 3 Nov 2021 21:45:44 +0000 [thread overview]
Message-ID: <YYMDCPNuUdt2EukD@google.com> (raw)
In-Reply-To: <20211102032900.1888262-1-junaids@google.com>
On Mon, Nov 01, 2021, Junaid Shahid wrote:
> The fast page fault path bails out on write faults to huge pages in
> order to accommodate dirty logging. This change adds a check to do that
> only when dirty logging is actually enabled, so that access tracking for
> huge pages can still use the fast path for write faults in the common
> case.
>
> Signed-off-by: Junaid Shahid <junaids@google.com>
One nit, otherwise
Reviewed-by: Sean Christopherson <seanjc@google.com>
> ---
> arch/x86/kvm/mmu/mmu.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 354d2ca92df4..5df9181c5082 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -3191,8 +3191,9 @@ static int fast_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> new_spte |= PT_WRITABLE_MASK;
>
> /*
> - * Do not fix write-permission on the large spte. Since
> - * we only dirty the first page into the dirty-bitmap in
> + * Do not fix write-permission on the large spte when
> + * dirty logging is enabled. Since we only dirty the
> + * first page into the dirty-bitmap in
> * fast_pf_fix_direct_spte(), other pages are missed
> * if its slot has dirty logging enabled.
> *
> @@ -3201,7 +3202,8 @@ static int fast_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> *
> * See the comments in kvm_arch_commit_memory_region().
This part is slightly stale as kvm_mmu_slot_apply_flags() now has the comments.
Maybe just drop it entirely? The comments there don't do a whole lot to make this
code more understandable.
> */
> - if (sp->role.level > PG_LEVEL_4K)
> + if (sp->role.level > PG_LEVEL_4K &&
> + kvm_slot_dirty_track_enabled(fault->slot))
> break;
> }
>
> --
> 2.33.1.1089.g2158813163f-goog
>
prev parent reply other threads:[~2021-11-03 21:45 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-02 3:29 [PATCH] kvm: mmu: Use fast PF path for access tracking of huge pages when possible Junaid Shahid
2021-11-02 17:41 ` Ben Gardon
2021-11-03 21:45 ` Sean Christopherson [this message]
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