From 93c05d3ef25275829d421a255271595ac219a518 Mon Sep 17 00:00:00 2001 From: Xiao Guangrong Date: Sun, 13 Jan 2013 23:49:07 +0800 Subject: [PATCH] KVM: x86: improve reexecute_instruction The current reexecute_instruction can not well detect the failed instruction emulation. It allows guest to retry all the instructions except it accesses on error pfn For example, some cases are nested-write-protect - if the page we want to write is used as PDE but it chains to itself. Under this case, we should stop the emulation and report the case to userspace Reviewed-by: Gleb Natapov Signed-off-by: Xiao Guangrong Signed-off-by: Marcelo Tosatti --- arch/x86/include/asm/kvm_host.h | 7 +++++++ arch/x86/kvm/paging_tmpl.h | 27 ++++++++++++++++++++------- arch/x86/kvm/x86.c | 22 ++++++++++++++++++---- 3 files changed, 45 insertions(+), 11 deletions(-) diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index f75e1fe..77d56a4 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -497,6 +497,13 @@ struct kvm_vcpu_arch { u64 msr_val; struct gfn_to_hva_cache data; } pv_eoi; + + /* + * Indicate whether the access faults on its page table in guest + * which is set when fix page fault and used to detect unhandeable + * instruction. + */ + bool write_fault_to_shadow_pgtable; }; struct kvm_lpage_info { diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h index 3d1a352..ca69dcc 100644 --- a/arch/x86/kvm/paging_tmpl.h +++ b/arch/x86/kvm/paging_tmpl.h @@ -497,26 +497,34 @@ out_gpte_changed: * created when kvm establishes shadow page table that stop kvm using large * page size. Do it early can avoid unnecessary #PF and emulation. * + * @write_fault_to_shadow_pgtable will return true if the fault gfn is + * currently used as its page table. + * * Note: the PDPT page table is not checked for PAE-32 bit guest. It is ok * since the PDPT is always shadowed, that means, we can not use large page * size to map the gfn which is used as PDPT. */ static bool FNAME(is_self_change_mapping)(struct kvm_vcpu *vcpu, - struct guest_walker *walker, int user_fault) + struct guest_walker *walker, int user_fault, + bool *write_fault_to_shadow_pgtable) { int level; gfn_t mask = ~(KVM_PAGES_PER_HPAGE(walker->level) - 1); + bool self_changed = false; if (!(walker->pte_access & ACC_WRITE_MASK || (!is_write_protection(vcpu) && !user_fault))) return false; - for (level = walker->level; level <= walker->max_level; level++) - if (!((walker->gfn ^ walker->table_gfn[level - 1]) & mask)) - return true; + for (level = walker->level; level <= walker->max_level; level++) { + gfn_t gfn = walker->gfn ^ walker->table_gfn[level - 1]; + + self_changed |= !(gfn & mask); + *write_fault_to_shadow_pgtable |= !gfn; + } - return false; + return self_changed; } /* @@ -544,7 +552,7 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr, u32 error_code, int level = PT_PAGE_TABLE_LEVEL; int force_pt_level; unsigned long mmu_seq; - bool map_writable; + bool map_writable, is_self_change_mapping; pgprintk("%s: addr %lx err %x\n", __func__, addr, error_code); @@ -572,9 +580,14 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr, u32 error_code, return 0; } + vcpu->arch.write_fault_to_shadow_pgtable = false; + + is_self_change_mapping = FNAME(is_self_change_mapping)(vcpu, + &walker, user_fault, &vcpu->arch.write_fault_to_shadow_pgtable); + if (walker.level >= PT_DIRECTORY_LEVEL) force_pt_level = mapping_level_dirty_bitmap(vcpu, walker.gfn) - || FNAME(is_self_change_mapping)(vcpu, &walker, user_fault); + || is_self_change_mapping; else force_pt_level = 1; if (!force_pt_level) { diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 6f9cab0..e00dd05 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -4751,7 +4751,8 @@ static int handle_emulation_failure(struct kvm_vcpu *vcpu) return r; } -static bool reexecute_instruction(struct kvm_vcpu *vcpu, gva_t cr2) +static bool reexecute_instruction(struct kvm_vcpu *vcpu, gva_t cr2, + bool write_fault_to_shadow_pgtable) { gpa_t gpa = cr2; pfn_t pfn; @@ -4808,7 +4809,13 @@ static bool reexecute_instruction(struct kvm_vcpu *vcpu, gva_t cr2) * guest to let CPU execute the instruction. */ kvm_mmu_unprotect_page(vcpu->kvm, gpa_to_gfn(gpa)); - return true; + + /* + * If the access faults on its page table, it can not + * be fixed by unprotecting shadow page and it should + * be reported to userspace. + */ + return !write_fault_to_shadow_pgtable; } static bool retry_instruction(struct x86_emulate_ctxt *ctxt, @@ -4867,7 +4874,13 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, int r; struct x86_emulate_ctxt *ctxt = &vcpu->arch.emulate_ctxt; bool writeback = true; + bool write_fault_to_spt = vcpu->arch.write_fault_to_shadow_pgtable; + /* + * Clear write_fault_to_shadow_pgtable here to ensure it is + * never reused. + */ + vcpu->arch.write_fault_to_shadow_pgtable = false; kvm_clear_exception_queue(vcpu); if (!(emulation_type & EMULTYPE_NO_DECODE)) { @@ -4886,7 +4899,8 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, if (r != EMULATION_OK) { if (emulation_type & EMULTYPE_TRAP_UD) return EMULATE_FAIL; - if (reexecute_instruction(vcpu, cr2)) + if (reexecute_instruction(vcpu, cr2, + write_fault_to_spt)) return EMULATE_DONE; if (emulation_type & EMULTYPE_SKIP) return EMULATE_FAIL; @@ -4916,7 +4930,7 @@ restart: return EMULATE_DONE; if (r == EMULATION_FAILED) { - if (reexecute_instruction(vcpu, cr2)) + if (reexecute_instruction(vcpu, cr2, write_fault_to_spt)) return EMULATE_DONE; return handle_emulation_failure(vcpu); -- 2.7.4