On Sat, Dec 15, 2012 at 03:01:12PM +0800, Xiao Guangrong wrote: > 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 > > Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx> > --- > arch/x86/include/asm/kvm_host.h | 7 +++++ > arch/x86/kvm/paging_tmpl.h | 23 +++++++++++----- > arch/x86/kvm/x86.c | 58 +++++++++++++++++++++++++-------------- > 3 files changed, 60 insertions(+), 28 deletions(-) > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index dc87b65..487f0a1 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -502,6 +502,13 @@ struct kvm_vcpu_arch { > u64 msr_val; > struct gfn_to_hva_cache data; > } pv_eoi; > + > + /* > + * Cache the access info when fix page fault then use > + * them to detect unhandeable instruction. > + */ > + gva_t fault_addr; > + bool target_gfn_is_pt; > }; > > struct kvm_lpage_info { > diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h > index 0453fa0..b67fab3 100644 > --- a/arch/x86/kvm/paging_tmpl.h > +++ b/arch/x86/kvm/paging_tmpl.h > @@ -506,21 +506,27 @@ out_gpte_changed: > * size to map the gfn which is used as PDPT. > */ > static bool > -FNAME(is_self_change_mapping)(struct kvm_vcpu *vcpu, > +FNAME(is_self_change_mapping)(struct kvm_vcpu *vcpu, gva_t addr, > struct guest_walker *walker, int user_fault) > { > 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; > + vcpu->arch.fault_addr = addr; > > - return false; > + for (level = walker->level; level <= walker->max_level; level++) { > + gfn_t gfn = walker->gfn ^ walker->table_gfn[level - 1]; > + > + self_changed |= !(gfn & mask); > + vcpu->arch.target_gfn_is_pt |= !gfn; > + } > + > + return self_changed; > } > > /* > @@ -548,7 +554,7 @@ 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); > > @@ -576,9 +582,12 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr, u32 error_code, > return 0; > } > > + is_self_change_mapping = FNAME(is_self_change_mapping)(vcpu, addr, > + &walker, user_fault); > + is_self_change_mapping() has a subtle side-effect by setting vcpu->arch.target_gfn_is_pt. From reading the page_fault() function you cannot guess why is_self_change_mapping() is not called inside "if (walker.level >= PT_DIRECTORY_LEVEL)" since this is the only place where its output is used. May be pass it pointer to target_gfn_is_pt as a parameter to make it clear that return value is not the only output of the function. > 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 bf66169..fc33563 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -4756,29 +4756,25 @@ static int handle_emulation_failure(struct kvm_vcpu *vcpu) > static bool reexecute_instruction(struct kvm_vcpu *vcpu, unsigned long cr2) > { > gpa_t gpa = cr2; > + gfn_t gfn; > pfn_t pfn; > - unsigned int indirect_shadow_pages; > - > - spin_lock(&vcpu->kvm->mmu_lock); > - indirect_shadow_pages = vcpu->kvm->arch.indirect_shadow_pages; > - spin_unlock(&vcpu->kvm->mmu_lock); > - > - if (!indirect_shadow_pages) > - return false; > > if (!vcpu->arch.mmu.direct_map) { > - gpa = kvm_mmu_gva_to_gpa_read(vcpu, cr2, NULL); > + /* > + * Write permission should be allowed since only > + * write access need to be emulated. > + */ > + gpa = kvm_mmu_gva_to_gpa_write(vcpu, cr2, NULL); > + > + /* > + * If the mapping is invalid in guest, let cpu retry > + * it to generate fault. > + */ > if (gpa == UNMAPPED_GVA) > - return true; /* let cpu generate fault */ > + return true; > } Why not fold this change to if (!vcpu->arch.mmu.direct_map) into previous patch where it was introduced. This looks independent of what you are doing in this patch. > > - /* > - * if emulation was due to access to shadowed page table > - * and it failed try to unshadow page and re-enter the > - * guest to let CPU execute the instruction. > - */ > - if (kvm_mmu_unprotect_page(vcpu->kvm, gpa_to_gfn(gpa))) > - return true; > + gfn = gpa_to_gfn(gpa); > > /* > * Do not retry the unhandleable instruction if it faults on the > @@ -4786,13 +4782,33 @@ static bool reexecute_instruction(struct kvm_vcpu *vcpu, unsigned long cr2) > * retry instruction -> write #PF -> emulation fail -> retry > * instruction -> ... > */ > - pfn = gfn_to_pfn(vcpu->kvm, gpa_to_gfn(gpa)); > - if (!is_error_noslot_pfn(pfn)) { > - kvm_release_pfn_clean(pfn); > + pfn = gfn_to_pfn(vcpu->kvm, gfn); > + > + /* > + * If the instruction failed on the error pfn, it can not be fixed, > + * report the error to userspace. > + */ > + if (is_error_noslot_pfn(pfn)) > + return false; > + > + kvm_release_pfn_clean(pfn); > + > + /* The instructions are well-emulated on direct mmu. */ > + if (vcpu->arch.mmu.direct_map) { > + unsigned int indirect_shadow_pages; > + > + spin_lock(&vcpu->kvm->mmu_lock); > + indirect_shadow_pages = vcpu->kvm->arch.indirect_shadow_pages; > + spin_unlock(&vcpu->kvm->mmu_lock); > + > + if (indirect_shadow_pages) > + kvm_mmu_unprotect_page(vcpu->kvm, gfn); > + > return true; > } > > - return false; > + kvm_mmu_unprotect_page(vcpu->kvm, gfn); > + return !(vcpu->arch.fault_addr == cr2 && vcpu->arch.target_gfn_is_pt); Do you store fault_addr only to avoid using stale target_gfn_is_pt? If yes why not reset target_gfn_is_pt to false at the beginning of a page fault and get rid of fault_addr? > } > > static bool retry_instruction(struct x86_emulate_ctxt *ctxt, > -- > 1.7.7.6 -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html