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

Sean Christopherson
2020-06-05T21:43:33Z

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>
---
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