Re: [Xen-devel] [PATCH] libxl: Remove qxl support for the 4.3 release

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2013-05-28 at 19:09 +0100, Keir Fraser wrote:
> On 28/05/2013 17:51, "Ian Jackson" <Ian.Jackson@xxxxxxxxxxxxx> wrote:
> 
> > George Dunlap writes ("[PATCH] libxl: Remove qxl support for the 4.3
> > release"):
> >> The qxl drivers for Windows and Linux end up calling instructions
> >> that cannot be used for MMIO at the moment.  Just for the 4.3 release,
> >> remove qxl support.
> >> 
> >> This patch should be reverted as soon as the 4.4 development window opens.
> >> 
> >> The issue in question:
> >> 
> >> (XEN) emulate.c:88:d18 bad mmio size 16
> >> (XEN) io.c:201:d18 MMIO emulation failed @ 0033:7fd2de390430: f3 0f 6f
> >> 19 41 83 e8 403
> >> 
> >> The instruction in question is "movdqu (%rcx),%xmm3".  Xen knows how
> >> to emulate it, but unfortunately %xmm3 is 16 bytes long, and the interface
> >> between Xen and qemu at the moment would appear to only allow MMIO accesses
> >> of 8 bytes.
> >> 
> >> It's too late in the release cycle to find a fix or a workaround.
> > 
> > Acked-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> 
> It could be plumbed through hvmemul_do_io's multi-cycle read/write logic,
> and done as two 8-byte cycles to qemu. This would avoid bloating the ioreq
> structure that communicates to qemu.

Are you proposing we do this for 4.3? I'm not sure how big that change
would be in terms of impact (just that one instruction, any 16 byte
operand?).

Of course even if we did this for 4.3 we don't know what the next issue
will be with QXL.

Ian.


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