Re: [Xen-devel] Getting the XSAVE size from userspace

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 05.11.15 at 11:49, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 05/11/15 10:42, Jan Beulich wrote:
>>>>> On 05.11.15 at 10:52, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
>>> I need to get the XSAVE size from userspace. The easiest way seems to be
>>> to use the XEN_DOMCTL_getvcpuextstate hypercall, but that hypercall is
>>> not public / there's no xenctrl.h wrapper for it.
>> Before going into any detail of the rest of your mail - any reason you
>> can't just consult CPUID output?
> 
> It depends on precisely what you want.
> 
> CPUID.0xD[0].ecx gives you the maximum xsave area on this processor
> CPUID.0xD[0].ebx gives you the current size for the value in xcr0, but
> that is not very useful from userspace.

Why would the maximum size not be sufficient for most (all?) user
mode purposes?

Jan


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