From 660a293ea9be709b893d371fbc0328fcca33c33a Mon Sep 17 00:00:00 2001 From: Shaohua Li <shaohua.li@intel.com> Date: Tue, 27 Jul 2010 16:06:28 +0800 Subject: [PATCH] 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> --- arch/x86/mm/fault.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 51f7ee71d6c7..caec22906d7c 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -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); -- GitLab