[PATCH 1/2] kvm: mmu/x86: Remove redundant spte present check in mmu_set_spte

Mingwei Zhang
2021-07-21T05:15:13Z

Drop an unnecessary is_shadow_present_pte() check when updating the rmaps
after installing a non-MMIO SPTE. set_spte() is used only to create
shadow-present SPTEs, e.g. MMIO SPTEs are handled early on, mmu_set_spte()
runs with mmu_lock held for write, i.e. the SPTE can't be zapped between
writing the SPTE and updating the rmaps.

Opportunistically combine the "new SPTE" logic for large pages and rmaps.

No functional change intended.

Suggested-by: Ben Gardon <bgardon@google.com>
Signed-off-by: Mingwei Zhang <mizhang@google.com>
---
arch/x86/kvm/mmu/mmu.c | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index b888385d1933..c45ddd2c964f 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -2693,12 +2693,10 @@ static int mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
if (!was_rmapped && is_large_pte(*sptep))
++vcpu->kvm->stat.lpages;

- if (is_shadow_present_pte(*sptep)) {
- if (!was_rmapped) {
- rmap_count = rmap_add(vcpu, sptep, gfn);
- if (rmap_count > RMAP_RECYCLE_THRESHOLD)
- rmap_recycle(vcpu, sptep, gfn);
- }
+ if (!was_rmapped) {
+ rmap_count = rmap_add(vcpu, sptep, gfn);
+ if (rmap_count > RMAP_RECYCLE_THRESHOLD)
+ rmap_recycle(vcpu, sptep, gfn);
}

return ret;
--
2.32.0.402.g57bb445576-goog