From 7819026eefee53eaaac3fdce1a2f157c7ea943fe Mon Sep 17 00:00:00 2001 From: Marcelo Tosatti Date: Tue, 11 Dec 2007 19:12:27 -0500 Subject: 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 Signed-off-by: Avi Kivity --- drivers/kvm/paging_tmpl.h | 29 +++++++++++++++++++++-------- 1 file changed, 21 insertions(+), 8 deletions(-) (limited to 'drivers/kvm/paging_tmpl.h') diff --git a/drivers/kvm/paging_tmpl.h b/drivers/kvm/paging_tmpl.h index 3ab3fb635e1..fb19596c958 100644 --- a/drivers/kvm/paging_tmpl.h +++ b/drivers/kvm/paging_tmpl.h @@ -65,7 +65,8 @@ struct guest_walker { int level; gfn_t table_gfn[PT_MAX_FULL_LEVELS]; - pt_element_t pte; + pt_element_t ptes[PT_MAX_FULL_LEVELS]; + gpa_t pte_gpa[PT_MAX_FULL_LEVELS]; unsigned pt_access; unsigned pte_access; gfn_t gfn; @@ -150,6 +151,7 @@ walk: pte_gpa = gfn_to_gpa(table_gfn); pte_gpa += index * sizeof(pt_element_t); walker->table_gfn[walker->level - 1] = table_gfn; + walker->pte_gpa[walker->level - 1] = pte_gpa; pgprintk("%s: table_gfn[%d] %lx\n", __FUNCTION__, walker->level - 1, table_gfn); @@ -180,6 +182,8 @@ walk: pte_access = pt_access & FNAME(gpte_access)(vcpu, pte); + walker->ptes[walker->level - 1] = pte; + if (walker->level == PT_PAGE_TABLE_LEVEL) { walker->gfn = gpte_to_gfn(pte); break; @@ -209,9 +213,9 @@ walk: goto walk; pte |= PT_DIRTY_MASK; kvm_mmu_pte_write(vcpu, pte_gpa, (u8 *)&pte, sizeof(pte)); + walker->ptes[walker->level - 1] = pte; } - walker->pte = pte; walker->pt_access = pt_access; walker->pte_access = pte_access; pgprintk("%s: pte %llx pte_access %x pt_access %x\n", @@ -268,7 +272,7 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr, u64 *shadow_ent; unsigned access = walker->pt_access; - if (!is_present_pte(walker->pte)) + if (!is_present_pte(walker->ptes[walker->level - 1])) return NULL; shadow_addr = vcpu->mmu.root_hpa; @@ -285,6 +289,7 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr, u64 shadow_pte; int metaphysical; gfn_t table_gfn; + bool new_page = 0; shadow_ent = ((u64 *)__va(shadow_addr)) + index; if (is_shadow_present_pte(*shadow_ent)) { @@ -300,16 +305,23 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr, if (level - 1 == PT_PAGE_TABLE_LEVEL && walker->level == PT_DIRECTORY_LEVEL) { metaphysical = 1; - if (!is_dirty_pte(walker->pte)) + if (!is_dirty_pte(walker->ptes[level - 1])) access &= ~ACC_WRITE_MASK; - table_gfn = gpte_to_gfn(walker->pte); + table_gfn = gpte_to_gfn(walker->ptes[level - 1]); } else { metaphysical = 0; table_gfn = walker->table_gfn[level - 2]; } shadow_page = kvm_mmu_get_page(vcpu, table_gfn, addr, level-1, metaphysical, access, - shadow_ent); + shadow_ent, &new_page); + if (new_page && !metaphysical) { + pt_element_t curr_pte; + kvm_read_guest(vcpu->kvm, walker->pte_gpa[level - 2], + &curr_pte, sizeof(curr_pte)); + if (curr_pte != walker->ptes[level - 2]) + return NULL; + } shadow_addr = __pa(shadow_page->spt); shadow_pte = shadow_addr | PT_PRESENT_MASK | PT_ACCESSED_MASK | PT_WRITABLE_MASK | PT_USER_MASK; @@ -317,7 +329,8 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr, } mmu_set_spte(vcpu, shadow_ent, access, walker->pte_access & access, - user_fault, write_fault, walker->pte & PT_DIRTY_MASK, + user_fault, write_fault, + walker->ptes[walker->level-1] & PT_DIRTY_MASK, ptwrite, walker->gfn); return shadow_ent; @@ -382,7 +395,7 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr, /* * mmio: emulate if accessible, otherwise its a guest fault. */ - if (is_io_pte(*shadow_pte)) + if (shadow_pte && is_io_pte(*shadow_pte)) return 1; ++vcpu->stat.pf_fixed; -- cgit v1.2.2