Commit 660a293e authored Jul 27, 2010 by Shaohua Li Committed by H. Peter Anvin Aug 26, 2010

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>

parent 9b861528

arch/x86/mm/fault.c

+7 −1

Original line number	Diff line number	Diff line
		@@ -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);

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