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 18:23:55 +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 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 :)).

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!

Thanks,

Paolo