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Date: Tue, 26 May 2015 13:56:49 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 03/29] display: enable DIRTY_MEMORY_VGA
	tracking explicitly
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: Fam Zheng <famz@redhat.com>, "Michael S. Tsirkin" <mst@redhat.com>, Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>, QEMU Developers <qemu-devel@nongnu.org>, Stefan Hajnoczi <stefanha@redhat.com>, Aurelien Jarno <aurelien@aurel32.net>



On 26/05/2015 13:52, Peter Maydell wrote:
> On 26 May 2015 at 12:24, Paolo Bonzini <pbonzini@redhat.com> wrote:
>> > Peter, Mark, Aurelien, can you review and ack this patch?
> Could you provide some explanation/documentation of when a
> display device needs to set DIRTY_MEMORY_VGA (and when it
> doesn't)?

It needs to set it if it uses memory_region_get/set/clear_dirty with
DIRTY_MEMORY_VGA as the last argument.

> If we get it wrong is there any way to make qemu
> assert or otherwise catch the error?

It may be possible to check against mr->dirty_log_mask in
memory_region_get/set/clear_dirty.  However, it is just as likely to
have some corner case that is correct but triggers the assertion.

I haven't thought much about it, because a simple grep for
DIRTY_MEMORY_VGA will catch the device models that need care.

Paolo