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    SubjectRe: [PATCH 11/21] KVM: x86/mmu: Zero allocate shadow pages (outside of mmu_lock)
    On Fri, Jun 5, 2020 at 2:39 PM Sean Christopherson
    <sean.j.christopherson@intel.com> 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@google.com>
    > Cc: Peter Shier <pshier@google.com>
    > Cc: Junaid Shahid <junaids@google.com>
    > Cc: Jim Mattson <jmattson@google.com>
    > Suggested-by: Ben Gardon <bgardon@google.com>
    > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
    Reviewed-by: Ben Gardon <bgardon@google.com>
    > ---
    > 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
    >

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