linux-kernel - Re: [PATCH v5 6/6] mtrr, mm, x86: Enhance MTRR checks for KVA huge page mapping

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Message-ID: <20150519114437.GF4641@pd.tnic>
Date:	Tue, 19 May 2015 13:44:37 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Toshi Kani <toshi.kani@...com>
Cc:	akpm@...ux-foundation.org, hpa@...or.com, tglx@...utronix.de,
	mingo@...hat.com, linux-mm@...ck.org, x86@...nel.org,
	linux-kernel@...r.kernel.org, dave.hansen@...el.com,
	Elliott@...com, pebolle@...cali.nl, mcgrof@...e.com
Subject: Re: [PATCH v5 6/6] mtrr, mm, x86: Enhance MTRR checks for KVA huge
 page mapping

On Mon, May 18, 2015 at 03:53:14PM -0600, Toshi Kani wrote:
> On Mon, 2015-05-18 at 22:51 +0200, Borislav Petkov wrote:
> > On Mon, May 18, 2015 at 02:21:08PM -0600, Toshi Kani wrote:
> > > The caller is the one who makes the condition checks necessary to create
> > > a huge page mapping.
> > 
> > How? It would go and change MTRRs configuration and ranges and their
> > memory types so that a huge mapping succeeds?
> > 
> > Or go and try a different range?
> 
> Try with a smaller page size.
> 
> The callers, pud_set_huge() and pmd_set_huge(), check if the given range
> is safe with MTRRs for creating a huge page mapping.  If not, they fail
> the request, which leads their callers, ioremap_pud_range() and
> ioremap_pmd_range(), to retry with a smaller page size, i.e. 1GB -> 2MB
> -> 4KB.  4KB may not have overlap with MTRRs (hence no checking is
> necessary), which will succeed as before.

Ok, now *this* should be in the form of a comment over the KVA helpers,
not the MTRR aspect. Callers of those functions would have to know that
- they shouldn't care about MTRR setup.

The MTRR aspect with the 3 conditions should be only over
mtrr_type_lookup().

I'll integrate it into the patch.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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