Re: runtime regression with "x86/mm/pat: Emulate PAT when it is disabled"

From: Borislav Petkov
Date: Sat Mar 12 2016 - 07:03:39 EST

On Fri, Mar 11, 2016 at 11:29:54PM +0000, Richard Purdie wrote:
> ... and if I remember rightly, the CPU features the kvm* options
> provide vary quite widely and wasn't consistent.

How so? Please elaborate so that we can fix those.

Btw, your reproducer works fine with -cpu kvm32 - only vncviewer's
window gets killed after a "Rect too large: 640x480 at (0, 0)" but
when I reconnect again right after it I see an X window asking me to
calibrate my touch screen and I'm at a loss as to where my touch screen
is... :-P

> Tweaking the kernel to only enable PAT with MTRR sounds like a good
> fix,

Yeah, the idea is to basically switch to uncacheable memtype as when
MTRRs are disabled.


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