Re: [Xen-devel] SSE instruction emulation issues

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 10.07.15 at 14:00, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 09/07/15 20:32, Zhi Wang wrote:
>>     We found that MOVD instruction are used by some windows driver
>> during developing XenGT, and also we found this one:
>>
>> (XEN) MMIO emulation failed: d7v1 64bit @ 0010:fffff8000294e273 -> 66
>> 0f e7 00 48 83 c0 10 45 3
>> b cb 73 f0 45 85 c9 
> 
> Disassembly:
>    0:    66 0f e7 00              movntdq %xmm0,(%rax)
>    4:    48 83 c0 10              add    $0x10,%rax
>    8:    45 3b cb                 cmp    %r11d,%r9d
>    b:    73 f0                    jae    0xfffffffffffffffd
>    d:    45 85 c9                 test   %r9d,%r9d
> 
> The x86 instruction emulator does appear to have a decode for this
> instruction.  This failure suggests that the implementation is buggy.
> 
> To start with diagnosing, add a test case to
> tools/tests/x86_emulator/test_x86_emulator.c

Considering that we already test MOVDQU, the emulation of which
shares code with MOVNTDQ (which only differs in aspects not of
interest to the emulator) I'm not sure this will turn up anything
interesting. Perhaps an even easier step would be to simply run
the emulator test on the machine where the issue is seen? We're
playing some prefix byte tricks there... Otoh failure to execute
the constructed instruction would bring down the hypervisor.

Jan


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