Harvey Harrison wrote:
On Wed, 2008-01-23 at 16:05 -0800, Jeremy Fitzhardinge wrote:
===================================================================
--- a/arch/x86/mm/fault_32.c
+++ b/arch/x86/mm/fault_32.c
@@ -290,6 +290,53 @@ static int is_errata93(struct pt_regs *r
/*
+ * Handle a spurious fault caused by a stale TLB entry. This allows
+ * us to lazily refresh the TLB when increasing the permissions of a
+ * kernel page (RO -> RW or NX -> X). Doing it eagerly is very
+ * expensive since that implies doing a full cross-processor TLB
+ * flush, even if no stale TLB entries exist on other processors.
+ * There are no security implications to leaving a stale TLB when
+ * increasing the permissions on a page.
+ */
+static int spurious_fault(unsigned long address,
+ unsigned long error_code)
+{
+ pgd_t *pgd;
+ pud_t *pud;
+ pmd_t *pmd;
+ pte_t *pte;
+
+ /* Reserved-bit violation or user access to kernel space? */
+ if (error_code & (PF_USER | PF_RSVD))
+ return 0;
+
+ pgd = init_mm.pgd + pgd_index(address);
+ if (!pgd_present(*pgd))
+ return 0;
+
+ pud = pud_offset(pgd, address);
+ if (!pud_present(*pud))
+ return 0;
+
+ pmd = pmd_offset(pud, address);
+ if (!pmd_present(*pmd))
+ return 0;
+
+ pte = pte_offset_kernel(pmd, address);
+ if (!pte_present(*pte))
+ return 0;
+ if ((error_code & 0x02) && !pte_write(*pte))
+ return 0;
if ((error_code & PF_WRITE) && !pte_write(*pte))
return 0;
Oops, thanks. Overlooked that one.
How about dropping the #if and rely on the !pte_exec() test always
being false when _PAGE_NX = 0? The compiler should just trim this
all away.
from pgtable.h:
static inline int pte_exec(pte_t pte) { return !(pte_val(pte)
& _PAGE_NX); }
Thanks for reminding me; I thought of this the other day, but forgot to
do it. Will post an updated patch shortly.
J
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