Re: [PATCH] KVM: x86: XSAVE/XRSTOR live migration support

[Avi Kivity <avi@redhat.com>]

On 05/31/2010 02:21 PM, Sheng Yang wrote:
>
>> Need to reserve way more space here for future xsave growth.  I think at
>> least 4K.  LRB wa 32x512bit = 1K (though it probably isn't a candidate
>> for vmx).  Would be good to get an opinion from your processor architects.
>>
>> I don't think we need to detail the contents of the structures since
>> they're described by the SDM; so we can have just a large array that is
>> 1:1 with the xsave as saved by the fpu.
>>      
> I think we can reserve one page here. But one big array make it harder to work
> with QEmu CPUState. Do we need lots of marcos in QEmu to parse the array? Also
> it's easier to transfer get/set_fpu to get/set_xsave interface using current
> structure I think.
>    

We'll need that code somewhere, so we aren't losing anything by putting 
it in userspace (in fact, qemu already has to have most of this code 
since it supports fxsave/fxrstor emulation).

What we gain is that if we make a bug, it is easier to fix it in 
userspace than in the kernel.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.