linux-kernel - Re: [PATCH] x86/mm: fix regression with huge pages on PAE

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Message-ID: <1447112591.21443.35.camel@hpe.com>
Date:	Mon, 09 Nov 2015 16:43:11 -0700
From:	Toshi Kani <toshi.kani@....com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	hpa@...or.com, tglx@...utronix.de, mingo@...hat.com,
	akpm@...ux-foundation.org
Cc:	bp@...en8.de, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	x86@...nel.org, jgross@...e.com, konrad.wilk@...cle.com,
	elliott@....com, boris.ostrovsky@...cle.com
Subject: Re: [PATCH] x86/mm: fix regression with huge pages on PAE

On Tue, 2015-11-10 at 01:18 +0200, Kirill A. Shutemov wrote:
> Recent PAT patchset has caused issue on 32-bit PAE machines:
 :
> The problem is in pmd_pfn_mask() and pmd_flags_mask(). These helpers use
> PMD_PAGE_MASK to calculate resulting mask. PMD_PAGE_MASK is 'unsigned
> long', not 'unsigned long long' as physaddr_t. As result upper bits of
> resulting mask is truncated.
> 
> The patch reworks code to use PMD_SHIFT as base of mask calculation
> instead of PMD_PAGE_MASK.
> 
> pud_pfn_mask() and pud_flags_mask() aren't problematic since we don't
> have PUD page table level on 32-bit systems, but they reworked too to be
> consistent with PMD counterpart.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Reported-and-Tested-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> Fixes: f70abb0fc3da ("x86/asm: Fix pud/pmd interfaces to handle large PAT
> bit")
> Cc: Toshi Kani <toshi.kani@....com>
> ---
>  arch/x86/include/asm/pgtable_types.h | 14 ++++----------
>  1 file changed, 4 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/x86/include/asm/pgtable_types.h
> b/arch/x86/include/asm/pgtable_types.h
> index dd5b0aa9dd2f..c1e797266ce9 100644
> --- a/arch/x86/include/asm/pgtable_types.h
> +++ b/arch/x86/include/asm/pgtable_types.h
> @@ -279,17 +279,14 @@ static inline pmdval_t native_pmd_val(pmd_t pmd)
>  static inline pudval_t pud_pfn_mask(pud_t pud)
>  {
>  	if (native_pud_val(pud) & _PAGE_PSE)
> -		return PUD_PAGE_MASK & PHYSICAL_PAGE_MASK;
> +		return ~((1ULL << PUD_SHIFT) - 1) & PHYSICAL_PAGE_MASK;

Thanks for the fix!  Should we fix the PMD/PUD MASK/SIZE macros, so that we do
not hit the same issue again when they are used? 

--- a/arch/x86/include/asm/page_types.h
+++ b/arch/x86/include/asm/page_types.h
@@ -17,10 +17,10 @@
    (ie, 32-bit PAE). */
 #define PHYSICAL_PAGE_MASK     (((signed long)PAGE_MASK) & __PHYSICAL_MASK)

-#define PMD_PAGE_SIZE          (_AC(1, UL) << PMD_SHIFT)
+#define PMD_PAGE_SIZE          (_AC(1, ULL) << PMD_SHIFT)
 #define PMD_PAGE_MASK          (~(PMD_PAGE_SIZE-1))

-#define PUD_PAGE_SIZE          (_AC(1, UL) << PUD_SHIFT)
+#define PUD_PAGE_SIZE          (_AC(1, ULL) << PUD_SHIFT)
 #define PUD_PAGE_MASK          (~(PUD_PAGE_SIZE-1))

Thanks,
-Toshi
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