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

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Date:   Fri, 4 Aug 2017 09:23:29 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     brijesh.singh@....com, kvm@...r.kernel.org,
        thomas lendacky <thomas.lendacky@....com>, rkrcmar@...hat.com,
        joro@...tes.org, x86@...nel.org, linux-kernel@...r.kernel.org,
        mingo@...hat.com, hpa@...or.com, tglx@...utronix.de, bp@...e.de
Subject: Re: [PATCH v2 1/3] kvm: svm: Add support for additional SVM NPF error
 codes

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