linux-kernel - [PATCH] ix86: fix types used in pgprot cachability flags translations

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Date:	Mon, 25 Jan 2016 09:43:17 -0700
From:	"Jan Beulich" <JBeulich@...e.com>
To:	<mingo@...e.hu>, <tglx@...utronix.de>, <hpa@...or.com>
Cc:	"Juergen Gross" <JGross@...e.com>, <linux-kernel@...r.kernel.org>
Subject: [PATCH] ix86: fix types used in pgprot cachability flags
 translations

For PAE kernels "unsigned long" is not suitable to hold page protection
flags, since _PAGE_NX doesn't fit there. This is the reason for quite a
few W+X pages getting reported as insecure during boot (observed namely
for the entire initrd range).

Quite the other way around, "unsigned long" is inefficient for 64-bit
kernels when dealing with cachability flags alone - "unsigned int" is
sufficient here and allows for slightly smaller code to be generated.

Fixes: 281d4078be ("x86: Make page cache mode a real type")
Signed-off-by: Jan Beulich <jbeulich@...e.com>
Cc: Juergen Gross <jgross@...e.com> 
---
 arch/x86/include/asm/pgtable_types.h |    9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

--- 4.5-rc1/arch/x86/include/asm/pgtable_types.h
+++ 4.5-rc1-ix86-PAE-pgprot-xlat/arch/x86/include/asm/pgtable_types.h
@@ -357,9 +357,8 @@ static inline pgprot_t cachemode2pgprot(
 }
 static inline enum page_cache_mode pgprot2cachemode(pgprot_t pgprot)
 {
-	unsigned long masked;
+	unsigned int masked = pgprot_val(pgprot) & _PAGE_CACHE_MASK;
 
-	masked = pgprot_val(pgprot) & _PAGE_CACHE_MASK;
 	if (likely(masked == 0))
 		return 0;
 	return __pte2cachemode_tbl[__pte2cm_idx(masked)];
@@ -367,9 +366,8 @@ static inline enum page_cache_mode pgpro
 static inline pgprot_t pgprot_4k_2_large(pgprot_t pgprot)
 {
 	pgprot_t new;
-	unsigned long val;
+	pgprotval_t val = pgprot_val(pgprot);
 
-	val = pgprot_val(pgprot);
 	pgprot_val(new) = (val & ~(_PAGE_PAT | _PAGE_PAT_LARGE)) |
 		((val & _PAGE_PAT) << (_PAGE_BIT_PAT_LARGE - _PAGE_BIT_PAT));
 	return new;
@@ -377,9 +375,8 @@ static inline pgprot_t pgprot_4k_2_large
 static inline pgprot_t pgprot_large_2_4k(pgprot_t pgprot)
 {
 	pgprot_t new;
-	unsigned long val;
+	pgprotval_t val = pgprot_val(pgprot);
 
-	val = pgprot_val(pgprot);
 	pgprot_val(new) = (val & ~(_PAGE_PAT | _PAGE_PAT_LARGE)) |
 			  ((val & _PAGE_PAT_LARGE) >>
 			   (_PAGE_BIT_PAT_LARGE - _PAGE_BIT_PAT));