powerpc: Ignore reserved field in DCSR and PVR reads and writes

[Michael Ellerman]

On Thu, 2017-01-19 at 03:19:10 UTC, Anton Blanchard wrote:
> From: Anton Blanchard <anton at samba.org>
> 
> IBM bit 31 (for the rest of us - bit 0) is a reserved field in the
> instruction definition of mtspr and mfspr. Hardware is encouraged to
> (and does) ignore it.
> 
> As a result, if userspace executes an mtspr DSCR with the reserved bit
> set, we get a DSCR facility unavailable exception. The kernel fails to
> match against the expected value/mask, and we silently return to
> userspace to try and re-execute the same mtspr DSCR instruction. We
> loop forever until the process is killed.
> 
> We should do something here, and it seems mirroring what hardware does
> is the better option vs killing the process. While here, relax the
> matching of mfspr PVR too.
> 
> Signed-off-by: Anton Blanchard <anton at samba.org>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/178f358208ceb8b38e5cff3f815e0d

cheers