From ff76d506030daeeeb967be8b8a189bf7aee8e7a8 Mon Sep 17 00:00:00 2001 From: Kai Huang Date: Thu, 29 Apr 2021 16:12:26 +1200 Subject: [PATCH] KVM: x86/mmu: Avoid unnecessary page table allocation in kvm_tdp_mmu_map() In kvm_tdp_mmu_map(), while iterating TDP MMU page table entries, it is possible SPTE has already been frozen by another thread but the frozen is not done yet, for instance, when another thread is still in middle of zapping large page. In this case, the !is_shadow_present_pte() check for old SPTE in tdp_mmu_for_each_pte() may hit true, and in this case allocating new page table is unnecessary since tdp_mmu_set_spte_atomic() later will return false and page table will need to be freed. Add is_removed_spte() check before allocating new page table to avoid this. Signed-off-by: Kai Huang Message-Id: <20210429041226.50279-1-kai.huang@intel.com> Reviewed-by: Ben Gardon Signed-off-by: Paolo Bonzini --- arch/x86/kvm/mmu/tdp_mmu.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c index 88f69a6..3c82848 100644 --- a/arch/x86/kvm/mmu/tdp_mmu.c +++ b/arch/x86/kvm/mmu/tdp_mmu.c @@ -1009,6 +1009,14 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code, } if (!is_shadow_present_pte(iter.old_spte)) { + /* + * If SPTE has been forzen by another thread, just + * give up and retry, avoiding unnecessary page table + * allocation and free. + */ + if (is_removed_spte(iter.old_spte)) + break; + sp = alloc_tdp_mmu_page(vcpu, iter.gfn, iter.level); child_pt = sp->spt; -- 2.7.4