linux-kernel - Re: [PATCH 1/2] x86: Fix pXd_flags() to handle _PAGE_PAT

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Date:	Fri, 10 Jul 2015 15:15:22 -0600
From:	Toshi Kani <toshi.kani@...com>
To:	Juergen Gross <jgross@...e.com>, hpa@...or.com, tglx@...utronix.de,
	mingo@...hat.com
Cc:	akpm@...ux-foundation.org, bp@...en8.de, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, x86@...nel.org,
	konrad.wilk@...cle.com, elliott@...com
Subject: Re: [PATCH 1/2] x86: Fix pXd_flags() to handle _PAGE_PAT_LARGE

On Fri, 2015-07-10 at 05:57 +0200, Juergen Gross wrote:
> On 07/09/2015 07:03 PM, Toshi Kani wrote:
> > The PAT bit gets relocated to bit 12 when PUD and PMD mappings are
> > used.  This bit 12, however, is not covered by PTE_FLAGS_MASK, 
> > which
> > is corrently used for masking the flag bits for all cases.
> > 
> > Fix pud_flags() and pmd_flags() to cover the PAT bit, 
> > _PAGE_PAT_LARGE,
> > when they are used to map a large page with _PAGE_PSE set.
  :
> Hmm, I think this covers only half of the problem. pud_pfn() and
> pmd_pfn() will return wrong results for large pages with PAT bit
> set as well.
> 
> I'd rather use something like:
> 
> static inline unsigned long pmd_pfn_mask(pmd_t pmd)
> {
> 	if (pmd_large(pmd))
> 		return PMD_PAGE_MASK & PHYSICAL_PAGE_MASK;
> 	else
> 		return PTE_PFN_MASK;
> }
> 
> static inline unsigned long pmd_flags_mask(pmd_t pmd)
> {
> 	if (pmd_large(pmd))
> 		return ~(PMD_PAGE_MASK & PHYSICAL_PAGE_MASK);
> 	else
> 		return ~PTE_PFN_MASK;
> }
> 
> static inline unsigned long pmd_pfn(pmd_t pmd)
> {
>          return (pmd_val(pmd) & pmd_pfn_mask(pmd)) >> PAGE_SHIFT;
> }
> 
> static inline pmdval_t pmd_flags(pmd_t pmd)
> {
> 	return native_pmd_val(pmd) & ~pmd_flags_mask(pmd);
> }

Thanks for the suggestion!  I agree that it is cleaner in this way.  I
am updating the patches and found the following changes are needed as
well:

 - Define PGTABLE_LEVELS to 2 in
"arch/x86/entry/vdso/vdso32/vclock_gettime.c".  This file redefines to
X86_32.  Setting to 2 levels (since X86_PAE is not set) allows <asm
-generic/pgtable-nopmd.h> be included to define PMD_SHIFT.

 - Move PUD_PAGE_SIZE & PUD_PAGE_MASK from <asm/page_64_types.h> to
<asm/page_types.h>.  This allows X86_32 to refer the PUD macros.

 - Nit: pmd_large() cannot be used in pmd_xxx_mask() since it calls
pmd_flags().  Use (native_pud_val(pud) & _PAGE_PSE), instead.

Thanks,
-Toshi
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