Re: [Xen-devel] [PATCH v6 08/16] x86/hvm: unify stdvga mmio intercept with standard mmio intercept

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 03.07.15 at 18:25, <paul.durrant@xxxxxxxxxx> wrote:
> It's clear from the following check in hvmemul_rep_movs:
> 
>     if ( sp2mt == p2m_mmio_direct || dp2mt == p2m_mmio_direct ||
>          (sp2mt == p2m_mmio_dm && dp2mt == p2m_mmio_dm) )
>         return X86EMUL_UNHANDLEABLE;
> 
> that mmio <-> mmio copy is not handled. This means the code in the
> stdvga mmio intercept that explicitly handles mmio <-> mmio copy when
> hvm_copy_to/from_guest_phys() fails is never going to be executed.

And in the end we have to realize that this is a regression introduced
by (afaict) 3bb4f99d8c ("x86 hvm: Replace old MMIO emulator with
x86_emulate()-based harness"). Whether there are any meaningful
use cases (i.e. whether addressing this would be needed/wanted)
isn't clear though - the only way I can trigger this (without creating a
DOS VM) is via leaving grub's gfx mode.

Jan


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