[PATCH v2 11/21] KVM: x86/mmu: Zero allocate shadow pages (outside of mmu_lock)

Sean Christopherson sean.j.christopherson at intel.com
Mon Jun 22 16:08:12 EDT 2020

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 at google.com>
Cc: Peter Shier <pshier at google.com>
Cc: Junaid Shahid <junaids at google.com>
Cc: Jim Mattson <jmattson at google.com>
Suggested-by: Ben Gardon <bgardon at google.com>
Reviewed-by: Ben Gardon <bgardon at google.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson at intel.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;

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