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>
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 51f7ee7..caec229 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -872,8 +872,14 @@
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);