KVM: MMU: Fix SMP shadow instantiation race
There is a race where VCPU0 is shadowing a pagetable entry while VCPU1 is updating it, which results in a stale shadow copy. Fix that by comparing the contents of the cached guest pte with the current guest pte after write-protecting the guest pagetable. Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com> Signed-off-by: Avi Kivity <avi@qumranet.com>
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parent
1d07543414
commit
7819026eef
2 changed files with 29 additions and 12 deletions
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@ -681,7 +681,8 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
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unsigned level,
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int metaphysical,
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unsigned access,
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u64 *parent_pte)
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u64 *parent_pte,
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bool *new_page)
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{
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union kvm_mmu_page_role role;
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unsigned index;
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@ -720,6 +721,8 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
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vcpu->mmu.prefetch_page(vcpu, sp);
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if (!metaphysical)
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rmap_write_protect(vcpu->kvm, gfn);
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if (new_page)
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*new_page = 1;
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return sp;
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}
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@ -993,7 +996,8 @@ static int nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, int write, gfn_t gfn)
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>> PAGE_SHIFT;
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new_table = kvm_mmu_get_page(vcpu, pseudo_gfn,
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v, level - 1,
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1, ACC_ALL, &table[index]);
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1, ACC_ALL, &table[index],
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NULL);
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if (!new_table) {
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pgprintk("nonpaging_map: ENOMEM\n");
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return -ENOMEM;
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@ -1059,7 +1063,7 @@ static void mmu_alloc_roots(struct kvm_vcpu *vcpu)
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ASSERT(!VALID_PAGE(root));
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sp = kvm_mmu_get_page(vcpu, root_gfn, 0,
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PT64_ROOT_LEVEL, 0, ACC_ALL, NULL);
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PT64_ROOT_LEVEL, 0, ACC_ALL, NULL, NULL);
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root = __pa(sp->spt);
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++sp->root_count;
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vcpu->mmu.root_hpa = root;
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@ -1080,7 +1084,7 @@ static void mmu_alloc_roots(struct kvm_vcpu *vcpu)
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root_gfn = 0;
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sp = kvm_mmu_get_page(vcpu, root_gfn, i << 30,
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PT32_ROOT_LEVEL, !is_paging(vcpu),
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ACC_ALL, NULL);
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ACC_ALL, NULL, NULL);
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root = __pa(sp->spt);
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++sp->root_count;
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vcpu->mmu.pae_root[i] = root | PT_PRESENT_MASK;
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@ -65,7 +65,8 @@
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struct guest_walker {
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int level;
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gfn_t table_gfn[PT_MAX_FULL_LEVELS];
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pt_element_t pte;
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pt_element_t ptes[PT_MAX_FULL_LEVELS];
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gpa_t pte_gpa[PT_MAX_FULL_LEVELS];
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unsigned pt_access;
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unsigned pte_access;
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gfn_t gfn;
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@ -150,6 +151,7 @@ walk:
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pte_gpa = gfn_to_gpa(table_gfn);
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pte_gpa += index * sizeof(pt_element_t);
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walker->table_gfn[walker->level - 1] = table_gfn;
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walker->pte_gpa[walker->level - 1] = pte_gpa;
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pgprintk("%s: table_gfn[%d] %lx\n", __FUNCTION__,
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walker->level - 1, table_gfn);
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@ -180,6 +182,8 @@ walk:
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pte_access = pt_access & FNAME(gpte_access)(vcpu, pte);
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walker->ptes[walker->level - 1] = pte;
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if (walker->level == PT_PAGE_TABLE_LEVEL) {
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walker->gfn = gpte_to_gfn(pte);
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break;
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@ -209,9 +213,9 @@ walk:
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goto walk;
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pte |= PT_DIRTY_MASK;
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kvm_mmu_pte_write(vcpu, pte_gpa, (u8 *)&pte, sizeof(pte));
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walker->ptes[walker->level - 1] = pte;
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}
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walker->pte = pte;
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walker->pt_access = pt_access;
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walker->pte_access = pte_access;
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pgprintk("%s: pte %llx pte_access %x pt_access %x\n",
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@ -268,7 +272,7 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
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u64 *shadow_ent;
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unsigned access = walker->pt_access;
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if (!is_present_pte(walker->pte))
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if (!is_present_pte(walker->ptes[walker->level - 1]))
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return NULL;
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shadow_addr = vcpu->mmu.root_hpa;
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@ -285,6 +289,7 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
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u64 shadow_pte;
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int metaphysical;
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gfn_t table_gfn;
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bool new_page = 0;
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shadow_ent = ((u64 *)__va(shadow_addr)) + index;
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if (is_shadow_present_pte(*shadow_ent)) {
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@ -300,16 +305,23 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
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if (level - 1 == PT_PAGE_TABLE_LEVEL
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&& walker->level == PT_DIRECTORY_LEVEL) {
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metaphysical = 1;
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if (!is_dirty_pte(walker->pte))
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if (!is_dirty_pte(walker->ptes[level - 1]))
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access &= ~ACC_WRITE_MASK;
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table_gfn = gpte_to_gfn(walker->pte);
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table_gfn = gpte_to_gfn(walker->ptes[level - 1]);
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} else {
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metaphysical = 0;
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table_gfn = walker->table_gfn[level - 2];
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}
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shadow_page = kvm_mmu_get_page(vcpu, table_gfn, addr, level-1,
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metaphysical, access,
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shadow_ent);
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shadow_ent, &new_page);
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if (new_page && !metaphysical) {
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pt_element_t curr_pte;
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kvm_read_guest(vcpu->kvm, walker->pte_gpa[level - 2],
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&curr_pte, sizeof(curr_pte));
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if (curr_pte != walker->ptes[level - 2])
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return NULL;
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}
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shadow_addr = __pa(shadow_page->spt);
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shadow_pte = shadow_addr | PT_PRESENT_MASK | PT_ACCESSED_MASK
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| PT_WRITABLE_MASK | PT_USER_MASK;
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@ -317,7 +329,8 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
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}
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mmu_set_spte(vcpu, shadow_ent, access, walker->pte_access & access,
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user_fault, write_fault, walker->pte & PT_DIRTY_MASK,
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user_fault, write_fault,
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walker->ptes[walker->level-1] & PT_DIRTY_MASK,
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ptwrite, walker->gfn);
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return shadow_ent;
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@ -382,7 +395,7 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr,
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/*
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* mmio: emulate if accessible, otherwise its a guest fault.
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*/
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if (is_io_pte(*shadow_pte))
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if (shadow_pte && is_io_pte(*shadow_pte))
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return 1;
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++vcpu->stat.pf_fixed;
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