Re: Compatibility between -device sga and -machine graphics=off

[Paolo Bonzini]

Oh, that's cool. It must be part of the kvmvapic migration data. Still, there are very likely some rare cases that would break (on any machine), e.g. if migrating while seabios is accessing the list of option roms.

Paolo

Il mer 8 set 2021, 18:36 Daniel P. Berrangé <berrange@redhat.com> ha scritto:

On Wed, Sep 08, 2021 at 06:28:01PM +0200, Paolo Bonzini wrote:
> On 08/09/21 18:08, Daniel P. Berrangé wrote:
> > Despite this difference, I was able migrate from a x86 guest using SGA
> > to a guest using graphics=off without errors being reported. So it
> > doesn't seem to change the migration data sections sent on the wire
> > at least.
>
> It would probably break with Windows XP/2003 guests on AMD processors, as
> those are the ones that use kvmvapic.  On other guests and processors, it's
> a no-op.

After running an incoming migrate, the target QEMU's  'info mtree'
changed to reflect what the src QEMU originally reported.  So whatever
difference 'graphics=off' causes compared to -device sga initially,
appears to have been eliminated by running the migrate. Not sure if
that's true in the general case or not - I'm just testing with a
minimalist CLI and no real OS running

 qemu-system-x86_64 -nodefaults -display sdl -device VGA -serial stdio  -device sga

vs

 qemu-system-x86_64 -nodefaults -display sdl -device VGA -serial stdio  -machine graphics=off

Regards,
Daniel
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