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

[Keir Fraser <keir.xen@xxxxxxxxx>]

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.

 -- Keir

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