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()? -- 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
