linux-kernel - Re: Intel's response Linux/MTRR/8GB Memory Support / Why doesn't the kernel realize the BIOS has problems and re-map appropriately?

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Message-ID: <Pine.LNX.4.64.0706020443490.32599@p34.internal.lan>
Date:	Sat, 2 Jun 2007 04:43:59 -0400 (EDT)
From:	Justin Piszcz <jpiszcz@...idpixels.com>
To:	Jesse Barnes <jbarnes@...tuousgeek.org>
cc:	Venki Pallipadi <venkatesh.pallipadi@...el.com>,
	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org
Subject: Re: Intel's response Linux/MTRR/8GB Memory Support / Why doesn't
 the kernel realize the BIOS has problems and re-map appropriately?



On Fri, 1 Jun 2007, Jesse Barnes wrote:

> On Friday, June 1, 2007 6:05:39 Venki Pallipadi wrote:
>> On Fri, Jun 01, 2007 at 02:41:57PM -0700, Jesse Barnes wrote:
>>> On Friday, June 1, 2007 2:19:43 Andi Kleen wrote:
>>>> And normally the MTRRs win, don't they (if I remember the table
>>>> correctly) So if the MTRR says UC and PAT disagrees it might not
>>>> actually help
>>>
>>> I just checked, yes the MTRRs win for UC types.  But it sounds like the
>>> cases we're talking about are actually situations where there's no MTRR
>>> coverage, so the default type is used.  The manual doesn't specifically
>>> call out how memory using the default type interacts with PAT, but it may
>>> well be that it stays uncached if the default type is uncached.  Again
>>> that argues for fixing the MTRR mapping problem in some way.
>>
>> I feel, having a silent/transparent workaround is not a good idea. With
>> that chances are BIOS bug will go unnoticed (having an error message in
>> dmesg may not get noticed either). Probably we should just panic at boot
>> with a
>> detailed message about the e820 mtrr discrepancy (which can be logged as
>> a BUG to BIOS provider) and suggest a temporary workaround of "mem=___".
>
> That might be best, short of actually fixing the MTRRs...
>
> Jesse
>
>

Indeed, at least it will inform the user of -what- is going on.
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