Under ARM64, PTEs can be broadly categorised as follows:
- Present and valid: Bit #0 is set. The PTE is valid and memory
access to the region may fault.
- Present and invalid: Bit #0 is clear and bit #1 is set.
Represents present memory with PROT_NONE protection. The PTE
is an invalid entry, and the user fault handler will raise a
SIGSEGV.
- Not present (file): Bits #0 and #1 are clear, bit #2 is set.
Memory represented has been paged out. The PTE is an invalid
entry, and the fault handler will try and re-populate the
memory where necessary.
Huge PTEs are block descriptors that have bit #1 clear. If we wish
to represent PROT_NONE huge PTEs we then run into a problem as
there is no way to distinguish between regular and huge PTEs if we
set bit #1.
As huge PTEs are always present, the meaning of bits #1 and #2 can
be swapped for invalid PTEs. This patch swaps the PTE_FILE and
PTE_PROT_NONE constants, allowing us to represent PROT_NONE huge
PTEs.
Signed-off-by: Steve Capper <steve.capper@xxxxxxxxxx>
---
arch/arm64/include/asm/pgtable.h | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index b1a1b59..e245260 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -25,8 +25,8 @@
* Software defined PTE bits definition.
*/
#define PTE_VALID (_AT(pteval_t, 1) << 0)
-#define PTE_PROT_NONE (_AT(pteval_t, 1) << 1) /* only when !PTE_VALID */
-#define PTE_FILE (_AT(pteval_t, 1) << 2) /* only when !pte_present() */
+#define PTE_FILE (_AT(pteval_t, 1) << 1) /* only when !pte_present() */
+#define PTE_PROT_NONE (_AT(pteval_t, 1) << 2) /* only when !PTE_VALID */
#define PTE_DIRTY (_AT(pteval_t, 1) << 55)
#define PTE_SPECIAL (_AT(pteval_t, 1) << 56)
@@ -306,8 +306,8 @@ extern pgd_t idmap_pg_dir[PTRS_PER_PGD];
/*
* Encode and decode a file entry:
- * bits 0-1: present (must be zero)
- * bit 2: PTE_FILE
+ * bits 0 & 2: present (must be zero)
+ * bit 1: PTE_FILE
* bits 3-63: file offset / PAGE_SIZE
*/
#define pte_file(pte) (pte_val(pte) & PTE_FILE)
--
1.8.1.4
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