KVM: x86/mmu: Zero allocate shadow pages (outside of mmu_lock)

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>
Reviewed-by: Ben Gardon <bgardon@google.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200703023545.8771-12-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 6e57044..a9fb427 100644 (file)
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -2535,7 +2535,6 @@ trace_get_page:
                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);
@@ -5708,6 +5707,8 @@ 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;