linux-kernel - Re: [PATCH v4 RESEND 4/11] x86/asm: Fix pud/pmd interfaces to handle large PAT bit

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Date:	Mon, 09 Nov 2015 14:01:44 -0700
From:	Toshi Kani <toshi.kani@....com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	Boris Ostrovsky <boris.ostrovsky@...cle.com>, hpa@...or.com,
	tglx@...utronix.de, mingo@...hat.com, akpm@...ux-foundation.org,
	bp@...en8.de, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	x86@...nel.org, jgross@...e.com, konrad.wilk@...cle.com,
	elliott@....com
Subject: Re: [PATCH v4 RESEND 4/11] x86/asm: Fix pud/pmd interfaces to
 handle large PAT bit

On Mon, 2015-11-09 at 22:10 +0200, Kirill A. Shutemov wrote:
> On Mon, Nov 09, 2015 at 12:16:41PM -0700, Toshi Kani wrote:
> > On Mon, 2015-11-09 at 13:06 -0500, Boris Ostrovsky wrote:
> > > On 09/17/2015 02:24 PM, Toshi Kani wrote:
> > > > Now that we have pud/pmd mask interfaces, which handle pfn & flags
> > > > mask properly for the large PAT bit.
> > > > 
> > > > Fix pud/pmd pfn & flags interfaces by replacing PTE_PFN_MASK and
> > > > PTE_FLAGS_MASK with the pud/pmd mask interfaces.
> > > > 
> > > > Suggested-by: Juergen Gross <jgross@...e.com>
> > > > Signed-off-by: Toshi Kani <toshi.kani@....com>
> > > > Cc: Juergen Gross <jgross@...e.com>
> > > > Cc: Konrad Wilk <konrad.wilk@...cle.com>
> > > > Cc: Thomas Gleixner <tglx@...utronix.de>
> > > > Cc: H. Peter Anvin <hpa@...or.com>
> > > > Cc: Ingo Molnar <mingo@...hat.com>
> > > > Cc: Borislav Petkov <bp@...en8.de>
> > > > ---
> > > >   arch/x86/include/asm/pgtable.h       |   14 ++++++++------
> > > >   arch/x86/include/asm/pgtable_types.h |    4 ++--
> > > >   2 files changed, 10 insertions(+), 8 deletions(-)
> > > > 
> > > 
> > > 
> > > Looks like this commit is causing this splat for 32-bit kernels. I am 
> > > attaching my config file, just in case.
> > 
> > Thanks for the report!  I'd like to reproduce the issue since I am not sure 
> > how this change caused it...
> > 
> > I tried to build a kernel with the attached config file, and got the 
> > following error.  Not sure what I am missing.  
> 
> The problem is that PMD_PAGE_MASK as well as PUD_PAGE_MASK are 'unsigned
> long', not 'unsigned long long'. So on 32-bit with PAE enabled your
> pmd_pfn_mask()/pud_pfn_mask() will truncate bits 32..43 of pmd/pudval and
> you'll never get proper page frame for pages above 4G.

Thanks Kirill!  Yes, this explains the issue.  Since I did not change these
MASKs, and I tested 32-bit kernels on a small system, I was not able to catch
this issue...
-Toshi
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