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

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Message-ID: <20160312120303.GA23469@pd.tnic>
Date:	Sat, 12 Mar 2016 13:03:03 +0100
From:	Borislav Petkov <bp@...e.de>
To:	Richard Purdie <richard.purdie@...uxfoundation.org>
Cc:	Bruce Ashfield <bruce.ashfield@...driver.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Toshi Kani <toshi.kani@....com>,
	Toshi Kani <toshi.kani@...com>,
	"Hart, Darren" <darren.hart@...el.com>,
	"saul.wold" <saul.wold@...el.com>, linux-kernel@...r.kernel.org,
	kvm ML <kvm@...r.kernel.org>, x86-ml <x86@...nel.org>
Subject: Re: runtime regression with "x86/mm/pat: Emulate PAT when it is
 disabled"

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.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--