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

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Date:	Mon, 07 Mar 2016 16:38:32 -0700
From:	Toshi Kani <toshi.kani@....com>
To:	Paul Gortmaker <paul.gortmaker@...driver.com>
Cc:	Borislav Petkov <bp@...e.de>,
	Richard Purdie <richard.purdie@...uxfoundation.org>,
	Toshi Kani <toshi.kani@...com>,
	Bruce Ashfield <bruce.ashfield@...driver.com>,
	"Hart, Darren" <darren.hart@...el.com>,
	"saul.wold" <saul.wold@...el.com>, linux-kernel@...r.kernel.org
Subject: Re: runtime regression with "x86/mm/pat: Emulate PAT when it is
 disabled"

On Mon, 2016-03-07 at 16:08 -0500, Paul Gortmaker wrote:
> [dropping oe list and lkml since attaching dmesg files.]
> 
> [Re: runtime regression with "x86/mm/pat: Emulate PAT when it is
> disabled"] On 07/03/2016 (Mon 09:03) Toshi Kani wrote:
> 
> > On Sun, 2016-03-06 at 19:35 -0500, Paul Gortmaker wrote:
> > > [Re: runtime regression with "x86/mm/pat: Emulate PAT when it is
> > > disabled"] On 04/03/2016 (Fri 15:12) Toshi Kani wrote:
> > > 
> > > > On Fri, 2016-03-04 at 13:37 -0500, Paul Gortmaker wrote:
> > > > > [Re: runtime regression with "x86/mm/pat: Emulate PAT when it is
> > > > > disabled"] On 03/03/2016 (Thu 22:02) Toshi Kani wrote:
> > > > > 
> > :
> > > > I am not really sure what I am doing is correct.
> > > > 
> > > > On one window:
> > > > # ./00-runme
> > > > Warning: vlan 0 is not connected to host network
> > > > VNC server running on '::1:5900'
> > > 
> > > Ah, it seems for some reason your system confuses qemu from using the
> > > "normal"  IPv4 default.   Try editing ./00-runme and add an explicit
> > > vnc option    "-vnc 127.0.0.1:5" in front of "-show-cursor" and then:
> > > 
> > > > 
> > > > And another window on the same system:
> > > > # vncviewer localhost:1
> > > 
> > > ...connect to localhost:5  here.  I chose 5 just to not bump into
> > > anything your system might have on :0 or :1 already.
> > 
> > Still no luck.  Perhaps, vlan needs to connect?
> > 
> > # ./00-runme
> > Warning: vlan 0 is not connected to host network
> 
> Nope, I get that too, it isn't critical.
> > 
> > # vncviewer localhost:5
> > 
> > TigerVNC Viewer 64-bit v1.6.0
> > Built on: 2016-01-04 15:09
> > Copyright (C) 1999-2015 TigerVNC Team and many others (see README.txt)
> > See http://www.tigervnc.org for information on TigerVNC.
> > Can't open display: 
> > 
> > > I'm assuming everyone here is used to reading diffs, but if someone
> > > wants the full dmesg files let me know and I'll send them off-list.
> > 
> > Yes, please send me full dmesg files.  Since I do not know your
> > original state, the diff does not give me the whole picture.
> 
> Attached.

Thanks for the dmesg files!  As I suspected, there is no message from
pat_init() in both cases.  That is, you are missing the following message,
which shows how PAT is configured to support cache attributes.

# dmesg | grep PAT
[0.000000] x86/PAT: Configuration [0-7]: WB  WC  UC- UC  WB  WC  UC- WT  

It may have seemed working before, but you did not have WC configured to
PAT without calling pat_init().  There was not a proper check in place to
detect this error before.  Can you please check your code to see what
caused this skip of pat_init()?  If you have a git tree, I can take a look
as well. 

-Toshi