Re: [Xen-devel] [PATCH] [RFC] x86/cpu: Fix SMAP check in PVOPS environments

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 20/04/15 18:09, Andrew Cooper wrote:
> There appears to be no formal statement of what pv_irq_ops.save_fl() is
> supposed to return precisely.  Native returns the full flags, while lguest and
> Xen only return the Interrupt Flag, and both have comments by the
> implementations stating that only the Interrupt Flag is looked at.  This may
> have been true when initially implemented, but no longer is.
> 
> To make matters worse, the Xen PVOP leaves the upper bits undefined, making
> the BUG_ON() undefined behaviour.  Experimentally, this now trips for 32bit PV
> guests on Broadwell hardware.  The BUG_ON() is consistent for an individual
> build, but not consistent for all builds.  It has also been a sitting timebomb
> since SMAP support was introduced.
> 
> Use native_save_fl() instead, which will obtain an accurate view of the AC
> flag.

Reviewed-by: David Vrabel <david.vrabel@xxxxxxxxxx>

David


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