Re: [PATCH v2 3/4] x86/xstate: fix fault behavior on XRSTORS

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 01/02/16 09:13, Jan Beulich wrote:
> XRSTORS unconditionally faults when xcomp_bv has bit 63 clear. Instead
> of just fixing this issue, overhaul the fault recovery code, which -
> one of the many mistakes made when xstate support got introduced - was
> blindly mirroring that accompanying FXRSTOR, neglecting the fact that
> XRSTOR{,S} aren't all-or-nothing instructions. The new code, first of
> all, does all the recovery actions in C, simplifying the inline
> assembly used. And it does its work in a multi-stage fashion: Upon
> first seeing a fault, state fixups get applied strictly based on what
> architecturally may cause #GP. When seeing another fault despite the
> fixups done, state gets fully reset. A third fault would then lead to
> crashing the domain (instead of hanging the hypervisor in an infinite
> loop of recurring faults).
>
> Reported-by: Harmandeep Kaur <write.harmandeep@gmail.com>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> ---
> v2: Fix default MXCSR mask value. Avoid infinite fault recovery loop.

Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>