Re: [PATCH v2 1/3] kvm: svm: Add support for additional SVM NPF error codes

Brijesh Singh
2017-08-04T14:23:42Z

Hi Paolo,

On 08/04/2017 09:05 AM, Paolo Bonzini wrote:
> On 04/08/2017 02:30, Brijesh Singh wrote:
>>
>>
>> On 8/2/17 5:42 AM, Paolo Bonzini wrote:
>>> On 01/08/2017 15:36, Brijesh Singh wrote:
>>>>> The flow is:
>>>>>
>>>>> hardware walks page table; L2 page table points to read only memory
>>>>> -> pf_interception (code =
>>>>> -> kvm_handle_page_fault (need_unprotect = false)
>>>>> -> kvm_mmu_page_fault
>>>>> -> paging64_page_fault (for example)
>>>>> -> try_async_pf
>>>>> map_writable set to false
>>>>> -> paging64_fetch(write_fault = true, map_writable = false,
>>>>> prefault = false)
>>>>> -> mmu_set_spte(speculative = false, host_writable = false,
>>>>> write_fault = true)
>>>>> -> set_spte
>>>>> mmu_need_write_protect returns true
>>>>> return true
>>>>> write_fault == true -> set emulate = true
>>>>> return true
>>>>> return true
>>>>> return true
>>>>> emulate
>>>>>
>>>>> Without this patch, emulation would have called
>>>>>
>>>>> ..._gva_to_gpa_nested
>>>>> -> translate_nested_gpa
>>>>> -> paging64_gva_to_gpa
>>>>> -> paging64_walk_addr
>>>>> -> paging64_walk_addr_generic
>>>>> set fault (nested_page_fault=true)
>>>>>
>>>>> and then:
>>>>>
>>>>> kvm_propagate_fault
>>>>> -> nested_svm_inject_npf_exit
>>>>>
>>>> maybe then safer thing would be to qualify the new error_code check with
>>>> !mmu_is_nested(vcpu) or something like that. So that way it would run on
>>>> L1 guest, and not the L2 guest. I believe that would restrict it avoid
>>>> hitting this case. Are you okay with this change ?
>>> Or check "vcpu->arch.mmu.direct_map"? That would be true when not using
>>> shadow pages.
>>
>> Yes that can be used.
>
> Are you going to send a patch for this?
>

Yes. I should be posting it by Monday or Tuesday - need sometime to verify it.

-Brijesh