Hi Gleb,
Thanks for your review and sorry for the delay reply since i was on my vacation.
On 12/23/2012 11:02 PM, Gleb Natapov wrote:
> On Sat, Dec 15, 2012 at 03:01:12PM +0800, Xiao Guangrong wrote:
>>
>> + 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.
Yes, it is clearer, will do it in the next version.
>
>> 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.
Fine to me.
>
>>
>> - /*
>> - * 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?
Good suggestion, will do. :)
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