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From: "Luis R. Rodriguez" <mcgrof@suse.com>
To: Toshi Kani <toshi.kani@hpe.com>
Cc: Prarit Bhargava <prarit@redhat.com>,
	Stuart Hayes <stuart.w.hayes@gmail.com>,
	tglx@linutronix.de, mingo@redhat.com,
	"H. Peter Anvin" <hpa@zytor.com>,
	linux-kernel@vger.kernel.org, x86@kernel.org,
	mcgrof@do-not-panic.com, Toshi Kani <toshi.kani@hp.com>
Subject: Re: Fwd: [PATCH] x86: Use larger chunks in mtrr_cleanup
Date: Thu, 3 Sep 2015 21:51:34 +0200	[thread overview]
Message-ID: <20150903195134.GW8051@wotan.suse.de> (raw)
In-Reply-To: <1441308162.3277.20.camel@hpe.com>

On Thu, Sep 03, 2015 at 01:22:42PM -0600, Toshi Kani wrote:
> On Thu, 2015-09-03 at 20:40 +0200, Luis R. Rodriguez wrote:
> > On Thu, Sep 03, 2015 at 02:10:14PM -0400, Prarit Bhargava wrote:
> > > 
> > > 
> > > On 09/03/2015 01:59 PM, Luis R. Rodriguez wrote:
> > > > On Thu, Sep 03, 2015 at 08:17:02AM -0400, Prarit Bhargava wrote:
> > > > > 
> > > > > 
> > > > > On 09/02/2015 10:45 PM, Luis R. Rodriguez wrote:
> > > > > > On Mon, Aug 31, 2015 at 11:05:33AM -0500, Stuart Hayes wrote:
> > > > > > > Increase the range of chunk sizes tried in mtrr_cleanup() so it is 
> > > > > > > able to map large memory configs into MTRRs.
> > > > > > > 
> > > > > > > Currently, mtrr_cleanup() will fail with large memory 
> > > > > > > configurations, because it limits chunk_size to 2GB, which means 
> > > > > > > that each MTRR can only cover 2GB of memory.  With a memory size 
> > > > > > > of, say, 256GB, and ten variable MTRRs (such as some recent Intel 
> > > > > > > CPUs have), it is not possible to set up the MTRRs to cover all of
> > > > > > > memory.
> > > > > > 
> > > > > > Linux drivers no longer use MTRR so why is the cleanup needed, ie, 
> > > > > > what would happen if the cleanup is just skipped in your case ?
> > > > > 
> > > > > The infiniband & video drivers still use MTRR (or at least it was my
> > > > > understanding that they do). 
> > > > 
> > > > There were a few stragglers left on v4.2, I have transformed them in the 
> > > > latest development changes and those tranformations are now part of 
> > > > linux-next. If this is specific to a driver you may want to first ensure 
> > > > you backport the required patch that transforms the driver to use proper 
> > > > PAT interfaces, v4.2 should have most updates but there were still a few 
> > > > left. Just make sure your driver doesn't call mtrr_add() directly and if 
> > > > it doesn't then you should be OK.
> > > > 
> > > > > In any case, Stuart -- could you try booting with
> > > > > 'disable_mtrr_cleanup' as a kernel parameter?
> > > > 
> > > > Indeed, please I'd like to hear back. Be sure to have the respective 
> > > > driver transformation in place, what driver are you using exactly? In 
> > > > the event that you argue this is still needed I'd like to know exaclty 
> > > > *why*, the comit log does not mention any of that at all.
> > > > 
> > > 
> > > Well ... we are trying to also fix this in older kernels too, *cough* RHEL
> > > *cough*, so that's where the patch comes from.  If upstream is going to
> > > deprecate/remove mtrr support so be it. 
> > 
> > Check linux-next, and Documentation/x86/mtrr.txt
> > 
> > https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/tree/Docume
> > ntation/x86/mtrr.txt
> > 
> > The platform use of MTRR is the only thing you should be concerned over but 
> > as noted returning MTRR_TYPE_INVALID should suffice if the OS does not make
> > any driver use / modifications.
> 
> The following sentence in the "mtrr.txt" is not correct.  (Sorry I should have
> caught it earlier.)  mtrr_type_lookup() returns MTRR_TYPE_INVALID when MTRRs
> are disabled, i.e. MTRRs are not set by neither firmware nor OS.  Most of the
> firmwares enable them, though.
>
> "If MTRRs are only set up by the platform firmware code though and the OS does
> not make any specific MTRR mapping requests mtrr_type_lookup() should always
> return MTRR_TYPE_INVALID."

So this should be clarified to say -- that because platform firmware *may* make
use of MTRRs, even if all OS drivers are no longer making use of MTRRs
directly, we still need mtrr_type_lookup() to return the right type ?

 Luis

  reply	other threads:[~2015-09-03 19:51 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <55E477DE.2060106@gmail.com>
2015-08-31 16:05 ` Stuart Hayes
2015-09-03  2:45   ` Luis R. Rodriguez
2015-09-03 12:17     ` Prarit Bhargava
2015-09-03 17:59       ` Luis R. Rodriguez
2015-09-03 18:10         ` Prarit Bhargava
2015-09-03 18:40           ` Luis R. Rodriguez
2015-09-03 19:22             ` Toshi Kani
2015-09-03 19:51               ` Luis R. Rodriguez [this message]
2015-09-03 21:31                 ` Toshi Kani
2015-09-03 22:07                   ` Luis R. Rodriguez
2015-09-03 22:25                     ` Toshi Kani
2015-09-03 22:45                       ` Luis R. Rodriguez
2015-09-03 23:21                         ` Toshi Kani
2015-09-03 23:54                           ` Luis R. Rodriguez
2015-09-04  0:48                             ` Toshi Kani
2015-09-04  1:40                               ` Luis R. Rodriguez
2015-09-04 14:56                                 ` Toshi Kani
2015-09-04  6:51                             ` Jan Beulich
2015-09-14 14:46       ` Stuart Hayes
2015-11-05 19:14         ` Yinghai Lu
2015-11-05 19:43           ` Luis R. Rodriguez
2016-03-16 20:20             ` Luis R. Rodriguez
2016-03-29 17:07               ` Luis R. Rodriguez

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