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

On 28/05/13 19:09, 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
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.

Would this require changes to qemu?

It's definitely too late in the release cycle to be making this kind of change, especially because, as Ian said, we don't know how many more niggles we may run into if we fix this one.


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