From: "Luis R. Rodriguez" <mcgrof@suse.com>
To: Toshi Kani <toshi.kani@hp.com>
Cc: "Luis R. Rodriguez" <mcgrof@do-not-panic.com>,
"Tomi Valkeinen" <tomi.valkeinen@ti.com>,
"Borislav Petkov" <bp@suse.de>,
"Bjorn Helgaas" <bhelgaas@google.com>,
"Jej B" <James.Bottomley@hansenpartnership.com>,
"Ville Syrjälä" <syrjala@sci.fi>,
"Ville Syrjälä" <ville.syrjala@linux.intel.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
linux-media@vger.kernel.org,
linux-fbdev <linux-fbdev@vger.kernel.org>,
"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
"Andy Lutomirski" <luto@amacapital.net>,
"X86 ML" <x86@kernel.org>, "Juergen Gross" <jgross@suse.com>,
"Dave Airlie" <airlied@redhat.com>,
xen-devel@lists.xenproject.org,
"Julia Lawall" <julia.lawall@lip6.fr>
Subject: Re: RIP MTRR - status update for upcoming v4.2
Date: Fri, 12 Jun 2015 02:52:21 +0200 [thread overview]
Message-ID: <20150612005221.GD23057@wotan.suse.de> (raw)
In-Reply-To: <1434064996.11808.64.camel@misato.fc.hp.com>
On Thu, Jun 11, 2015 at 05:23:16PM -0600, Toshi Kani wrote:
> On Thu, 2015-06-11 at 13:36 -0700, Luis R. Rodriguez wrote:
> :
> > Pending RIP MTRR patches
> > ====================
> >
> > There are a few pending series so I wanted to provide a status update
> > on those series.
> >
> > mtrr: bury MTRR - unexport mtrr_add() and mtrr_del()
> >
> > This is the nail on the MTRR coffin, it will prevent future direct
> > access to MTRR code. This will not be posted until all of the below
> > patches are in and merged. A possible next step here might be to
> > consider separating PAT code from MTRR code and making PAT a first
> > class citizen, enabling distributions to disable MTRR code in the
> > future. I thought this was possible but for some reason I recently
> > thought that there was one possible issue to make this happen. I
> > suppose we won't know unless we try, unless of course someone already
> > knows, Toshi?
>
> There are two usages on MTRRs:
> 1) MTRR entries set by firmware
> 2) MTRR entries set by OS drivers
>
> We can obsolete 2), but we have no control over 1). As UEFI firmwares
> also set this up, this usage will continue to stay. So, we should not
> get rid of the MTRR code that looks up the MTRR entries, while we have
> no need to modify them.
>
> Such MTRR entries provide safe guard to /dev/mem, which allows
> privileged user to access a range that may require UC mapping while
> the /dev/mem driver blindly maps it with WB. MTRRs converts WB to UC in
> such a case.
>
> UEFI memory table has memory attribute, which describes cache types
> supported in physical memory ranges. However, this information gets
> lost when it it is converted to e820 table.
Is there no way to modify CPU capability bits upon boot and kick UEFI
to re-evaluate ? In such UEFI cases what happens for instance when
Xen is used which does not support MTRR?
Luis
next prev parent reply other threads:[~2015-06-12 0:52 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-11 20:36 RIP MTRR - status update for upcoming v4.2 Luis R. Rodriguez
2015-06-11 23:23 ` Toshi Kani
2015-06-12 0:52 ` Luis R. Rodriguez [this message]
2015-06-12 16:42 ` Toshi Kani
2015-06-12 7:59 ` [Xen-devel] " Jan Beulich
2015-06-12 16:58 ` Toshi Kani
2015-08-06 19:53 ` Luis R. Rodriguez
2015-08-06 19:55 ` Luis R. Rodriguez
2015-08-06 22:58 ` Toshi Kani
2015-08-07 20:25 ` Luis R. Rodriguez
2015-08-07 21:56 ` Toshi Kani
2015-08-07 22:23 ` Luis R. Rodriguez
2015-08-07 23:08 ` Toshi Kani
2015-08-07 23:19 ` Toshi Kani
2015-08-07 23:26 ` Luis R. Rodriguez
2015-08-07 23:48 ` Toshi Kani
2015-06-12 23:15 ` Andy Lutomirski
2015-06-12 23:29 ` James Bottomley
2015-06-13 6:37 ` Ingo Molnar
2015-06-15 6:20 ` Jan Beulich
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