Re: [Xen-devel] xsave=0 workaround needed on 3.2 kernels with Xen 4.1 or Xen-unstable.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 08.05.12 at 01:57, AP <apxeng@xxxxxxxxx> wrote:
> On Mon, May 7, 2012 at 7:15 AM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>> Sure, as it's a kernel problem. It's the kernel that needs logging added,
>> to find out why the CR4 write supposedly happening immediately
>> prior to the XSETBV (set_in_cr4(X86_CR4_OSXSAVE)) doesn't actually
>> happen, or doesn't set the flag. Perhaps something fishy going on
> 
> xen_write_cr4 explicitly turns off X86_CR4_OSXSAVE.
> 
> static void xen_write_cr4(unsigned long cr4)
> {
>     cr4 &= ~X86_CR4_PGE;
>     cr4 &= ~X86_CR4_PSE;
>     cr4 &= ~X86_CR4_OSXSAVE;
> 
>     native_write_cr4(cr4);
> }

That's definitely not the case in _any_ upstream Linux release.
Which means that this must be introduced by a distro-specific
(and broken) patch.

Jan


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