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x86, mm: Make spurious_fault check explicitly check the PRESENT bit 

pte_present() returns true even present bit isn't set but _PAGE_PROTNONE
(global bit) bit is set. While with CONFIG_DEBUG_PAGEALLOC, free pages have
global bit set but present bit clear. This patch makes we could catch
free pages access with CONFIG_DEBUG_PAGEALLOC enabled.

[ hpa: added a comment in the code as a warning to janitors ]

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
LKML-Reference: <1280217988.32400.75.camel@sli10-desk.sh.intel.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This commit is contained in:
Shaohua Li 2010-07-27 16:06:28 +08:00 committed by H. Peter Anvin
parent 9b861528a8
commit 660a293ea9
1 changed files with 7 additions and 1 deletions
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8
arch/x86/mm/fault.c
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@ -872,8 +872,14 @@ spurious_fault(unsigned long error_code, unsigned long address)
if (pmd_large(*pmd))
return spurious_fault_check(error_code, (pte_t *) pmd);
/*
* Note: don't use pte_present() here, since it returns true
* if the _PAGE_PROTNONE bit is set. However, this aliases the
* _PAGE_GLOBAL bit, which for kernel pages give false positives
* when CONFIG_DEBUG_PAGEALLOC is used.
*/
pte = pte_offset_kernel(pmd, address);
if (!pte_present(*pte))
if (!(pte_flags(*pte) & _PAGE_PRESENT))
return 0;
ret = spurious_fault_check(error_code, pte);