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Re: [Xen-devel] sse, mmx support for hvm guests

Masking from CPUID should work. I'm surprised it would cause a guest to fail
to boot.


On 25/10/08 23:30, "Ashish Bijlani" <ashish.bijlani@xxxxxxxxx> wrote:

> it's just masking the sse/mmx features from cpuid return value or
> something more to it? because i tried masking sse/mmx features from
> cpuid and now the hvm domain doesn't boot!! any idea if sse/mmx
> support can be disabled using bios?
> Thanks,
> Ashish
> On Sat, Oct 25, 2008 at 7:13 PM, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
> wrote:
>> On 25/10/08 20:34, "Ashish Bijlani" <ashish.bijlani@xxxxxxxxx> wrote:
>>> I've a quad-core x86_64 machine (Intel Xeon), with sse/mmx support.
>>> However, I want to disable sse/mmx support from HVM guests. How can I
>>> do this? Also, is it reasonable to expect illegal instruction fault in
>>> non-root VMX mode if a guest VM runs an application with sse/mmx
>>> instructions?
>> You can hide SSE/MMX in CPUID info, so the guest should not attempt to use
>> the instructions. This is obviously true since CPUID causes vmexit and then
>> the instruction is always emulated. But I don't think you can make the
>> sse/mmx instructions fault if the guest does actually try to use them
>> anyway.
>>  -- Keir

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