Re: [PATCH 11/21] KVM: x86/mmu: Zero allocate shadow pages (outside of mmu_lock)

[Ben Gardon]

On Fri, Jun 5, 2020 at 2:39 PM Sean Christopherson
<sean.j.christopherson@xxxxxxxxx> wrote:
>
> Set __GFP_ZERO for the shadow page memory cache and drop the explicit
> clear_page() from kvm_mmu_get_page().  This moves the cost of zeroing a
> page to the allocation time of the physical page, i.e. when topping up
> the memory caches, and thus avoids having to zero out an entire page
> while holding mmu_lock.
>
> Cc: Peter Feiner <pfeiner@xxxxxxxxxx>
> Cc: Peter Shier <pshier@xxxxxxxxxx>
> Cc: Junaid Shahid <junaids@xxxxxxxxxx>
> Cc: Jim Mattson <jmattson@xxxxxxxxxx>
> Suggested-by: Ben Gardon <bgardon@xxxxxxxxxx>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Reviewed-by: Ben Gardon <bgardon@xxxxxxxxxx>
> ---
>  arch/x86/kvm/mmu/mmu.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 6b0ec9060786..a8f8eebf67df 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -2545,7 +2545,6 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
>                 if (level > PG_LEVEL_4K && need_sync)
>                         flush |= kvm_sync_pages(vcpu, gfn, &invalid_list);
>         }
> -       clear_page(sp->spt);
>         trace_kvm_mmu_get_page(sp, true);
>
>         kvm_mmu_flush_or_zap(vcpu, &invalid_list, false, flush);
> @@ -5687,6 +5686,8 @@ int kvm_mmu_create(struct kvm_vcpu *vcpu)
>         vcpu->arch.mmu_page_header_cache.kmem_cache = mmu_page_header_cache;
>         vcpu->arch.mmu_page_header_cache.gfp_zero = __GFP_ZERO;
>
> +       vcpu->arch.mmu_shadow_page_cache.gfp_zero = __GFP_ZERO;
> +
>         vcpu->arch.mmu = &vcpu->arch.root_mmu;
>         vcpu->arch.walk_mmu = &vcpu->arch.root_mmu;
>
> --
> 2.26.0
>