linux-kernel - Re: [PATCH v2 3/3] kvm: svm: Use the hardware provided GPA instead of page walk

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Date:   Wed, 14 Dec 2016 19:47:12 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     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 3/3] kvm: svm: Use the hardware provided GPA instead of
 page walk



On 14/12/2016 19:39, Brijesh Singh wrote:
> 
> On 12/14/2016 11:23 AM, Paolo Bonzini wrote:
>>
>>
>> On 14/12/2016 18:07, Brijesh Singh wrote:
>>>>
>>>
>>> Since now we are going to perform multiple conditional checks before
>>> concluding that its safe to use HW provided GPA. How about if we add two
>>> functions "emulator_is_rep_string_op" and "emulator_is_two_mem_op" into
>>> emulator.c and  use these functions inside the x86.c to determine if its
>>> safe to use HW provided gpa?
>>
>> Why not export only emulator_can_use_gpa from emulate.c?  (So in the end
>> leaving emulator_is_string_op in emulate.c was the right thing to do, it
>> was just the test that was wrong :)).
>>
> 
> Actually, I was not sure if putting emulator_can_use_gpa() in emulate.c
> was right thing - mainly because emulator.c does not deal with GPA. I
> will go with your advice and put it in emulator.c, it makes easy :)
> 
> 
>> The patch below is still missing the check for cross-page MMIO.  Your
>> reference to the BKDG only covers MMCONFIG (sometimes referred to as
>> ECAM), not MMIO in general.  Doing AND or OR into video memory for
>> example is perfectly legal, and I'm fairly sure that some obscure legacy
>> software does PUSH/POP into vram as well!
>>
>>
> 
> I used your below code snippet to detect cross-page MMIO access. After
> applying these changes cross-page MMIO read/write unit test is passing
> just fine. I will include it in patch.

Great, thanks.  I hope we can include it in 4.10.

Paolo