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Message-ID: <1431985994.21526.12.camel@misato.fc.hp.com>
Date: Mon, 18 May 2015 15:53:14 -0600
From: Toshi Kani <toshi.kani@...com>
To: Borislav Petkov <bp@...en8.de>
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, 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.
Thanks,
-Toshi
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