On Wed, Nov 28, 2012 at 10:59:35PM +0800, Xiao Guangrong wrote: > On 11/28/2012 10:12 PM, Gleb Natapov wrote: > > On Tue, Nov 27, 2012 at 11:30:24AM +0800, Xiao Guangrong wrote: > >> On 11/27/2012 06:41 AM, Marcelo Tosatti wrote: > >> > >>>> > >>>> - return false; > >>>> +again: > >>>> + page_fault_count = ACCESS_ONCE(vcpu->kvm->arch.page_fault_count); > >>>> + > >>>> + /* > >>>> + * 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. > >>>> + */ > >>>> + kvm_mmu_unprotect_page(vcpu->kvm, gpa_to_gfn(gpa)); > >>>> + emulate = vcpu->arch.mmu.page_fault(vcpu, cr3, PFERR_WRITE_MASK, false); > >>> > >>> Can you explain what is the objective here? > >>> > >> > >> Sure. :) > >> > >> The instruction emulation is caused by fault access on cr3. After unprotect > >> the target page, we call vcpu->arch.mmu.page_fault to fix the mapping of cr3. > >> if it return 1, mmu can not fix the mapping, we should report the error, > >> otherwise it is good to return to guest and let it re-execute the instruction > >> again. > >> > >> page_fault_count is used to avoid the race on other vcpus, since after we > >> unprotect the target page, other cpu can enter page fault path and let the > >> page be write-protected again. > >> > >> This way can help us to detect all the case that mmu can not be fixed. > >> > > Can you write this in a comment above vcpu->arch.mmu.page_fault()? > > Okay, if Marcelo does not object this way. :) I do object, since it is possible to detect precisely the condition by storing which gfns have been cached. Then, Xiao, you need a way to handle large read-only sptes. -- 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
