Re: [PATCH] powerpc: fix 32-bit KVM-PR lockup and panic with MacOS guest

From: Benjamin Herrenschmidt
Date: Sun Feb 10 2019 - 20:20:05 EST

On Fri, 2019-02-08 at 14:51 +0000, Mark Cave-Ayland wrote:
> Indeed, but there are still some questions to be asked here:
> 1) Why were these bits removed from the original bitmask in the first place without
> it being documented in the commit message?
> 2) Is this the right fix? I'm told that MacOS guests already run without this patch
> on a G5 under 64-bit KVM-PR which may suggest that this is a workaround for another
> bug elsewhere in the 32-bit powerpc code.
> If you think that these points don't matter, then I'm happy to resubmit the patch
> as-is based upon your comments above.

We should write a test case to verify that FE0/FE1 are properly
preserved/context-switched etc... I bet if we accidentally wiped them,
we wouldn't notice 99.9% of the time.