From 00a669780ffa8c4b5f3e37346b5bf45508dd15bb Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Tue, 22 Jun 2021 10:56:55 -0700 Subject: [PATCH] KVM: x86/mmu: Use MMU role to check for matching guest page sizes Originally, __kvm_sync_page used to check the cr4_pae bit in the role to avoid zapping 4-byte kvm_mmu_pages when guest page size are 8-byte or the other way round. However, in commit 47c42e6b4192 ("KVM: x86: fix handling of role.cr4_pae and rename it to 'gpte_size'", 2019-03-28) it was observed that this did not work for nested EPT, where the page table size would be 8 bytes even if CR4.PAE=0. (Note that the check still has to be done for nested *NPT*, so it is not possible to use tdp_enabled or similar). Therefore, a hack was introduced to identify nested EPT shadow pages and unconditionally call __kvm_sync_page() on them. However, it is possible to do without the hack to identify nested EPT shadow pages: if EPT is active, there will be no shadow pages in non-EPT format, and all of them will have gpte_is_8_bytes set to true; we can just check the MMU role directly, and the test will always be true. Even for non-EPT shadow MMUs, this test should really always be true now that __kvm_sync_page() is called if and only if the role is an exact match (kvm_mmu_get_page()) or is part of the current MMU context (kvm_mmu_sync_roots()). A future commit will convert the likely-pointless check into a meaningful WARN to enforce that the mmu_roles of the current context and the shadow page are compatible. Cc: Vitaly Kuznetsov Signed-off-by: Sean Christopherson Message-Id: <20210622175739.3610207-11-seanjc@google.com> Signed-off-by: Paolo Bonzini --- Documentation/virt/kvm/mmu.rst | 3 --- arch/x86/kvm/mmu/mmu.c | 16 +++------------- 2 files changed, 3 insertions(+), 16 deletions(-) diff --git a/Documentation/virt/kvm/mmu.rst b/Documentation/virt/kvm/mmu.rst index 20d85daed395..ddbb23998742 100644 --- a/Documentation/virt/kvm/mmu.rst +++ b/Documentation/virt/kvm/mmu.rst @@ -192,9 +192,6 @@ Shadow pages contain the following information: Contains the value of cr4.smap && !cr0.wp for which the page is valid (pages for which this is true are different from other pages; see the treatment of cr0.wp=0 below). - role.ept_sp: - This is a virtual flag to denote a shadowed nested EPT page. ept_sp - is true if "cr0_wp && smap_andnot_wp", an otherwise invalid combination. role.smm: Is 1 if the page is valid in system management mode. This field determines which of the kvm_memslots array was used to build this diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 4af466f0ec6d..71a2ee755224 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -1780,16 +1780,13 @@ static void kvm_mmu_commit_zap_page(struct kvm *kvm, &(_kvm)->arch.mmu_page_hash[kvm_page_table_hashfn(_gfn)]) \ if ((_sp)->gfn != (_gfn) || (_sp)->role.direct) {} else -static inline bool is_ept_sp(struct kvm_mmu_page *sp) -{ - return sp->role.cr0_wp && sp->role.smap_andnot_wp; -} - /* @sp->gfn should be write-protected at the call site */ static bool __kvm_sync_page(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp, struct list_head *invalid_list) { - if ((!is_ept_sp(sp) && sp->role.gpte_is_8_bytes != !!is_pae(vcpu)) || + union kvm_mmu_page_role mmu_role = vcpu->arch.mmu->mmu_role.base; + + if (sp->role.gpte_is_8_bytes != mmu_role.gpte_is_8_bytes || vcpu->arch.mmu->sync_page(vcpu, sp) == 0) { kvm_mmu_prepare_zap_page(vcpu->kvm, sp, invalid_list); return false; @@ -4721,13 +4718,6 @@ kvm_calc_shadow_ept_root_page_role(struct kvm_vcpu *vcpu, bool accessed_dirty, role.base.guest_mode = true; role.base.access = ACC_ALL; - /* - * WP=1 and NOT_WP=1 is an impossible combination, use WP and the - * SMAP variation to denote shadow EPT entries. - */ - role.base.cr0_wp = true; - role.base.smap_andnot_wp = true; - role.ext = kvm_calc_mmu_role_ext(vcpu); role.ext.execonly = execonly;