Date: Sat, 12 Mar 2016 13:03:03 +0100
From: Borislav Petkov <bp@suse.de>
To: Richard Purdie <richard.purdie@linuxfoundation.org>
Cc: Bruce Ashfield <bruce.ashfield@windriver.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>,
        Paul Gortmaker <paul.gortmaker@windriver.com>,
        Toshi Kani <toshi.kani@hpe.com>, Toshi Kani <toshi.kani@hp.com>,
        "Hart, Darren" <darren.hart@intel.com>,
        "saul.wold" <saul.wold@intel.com>, linux-kernel@vger.kernel.org,
        kvm ML <kvm@vger.kernel.org>, x86-ml <x86@kernel.org>
Subject: Re: runtime regression with "x86/mm/pat: Emulate PAT when it is
 disabled"
Message-ID: <20160312120303.GA23469@pd.tnic>
References: <1457628591.15454.542.camel@hpe.com>
 <20160310172029.GA2194@pd.tnic>
 <20160310190429.GI23251@windriver.com>
 <20160310191933.GC2194@pd.tnic>
 <20160311132356.43a7b373@lxorguk.ukuu.org.uk>
 <20160311134000.GC4347@pd.tnic>
 <56E319FF.3090709@redhat.com>
 <20160311221651.GE4347@pd.tnic>
 <56E34695.2020300@windriver.com>
 <1457738994.2804.266.camel@linuxfoundation.org>
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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)
--