[004/156] mm/debug_vm_pgtable/ppc64: avoid setting top bits in radom value

Commit Message

Andrew Morton Oct. 16, 2020, 2:41 a.m. UTC

From: "Aneesh Kumar K.V" <[e-mail]>
Subject: mm/debug_vm_pgtable/ppc64: avoid setting top bits in radom value

ppc64 use bit 62 to indicate a pte entry (_PAGE_PTE).  Avoid setting that
bit in random value.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Aneesh Kumar K.V <[e-mail]>
Reviewed-by: Anshuman Khandual <[e-mail]>
Cc: Christophe Leroy <[e-mail]>
Cc: Michael Ellerman <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/debug_vm_pgtable.c |   13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

Patch

--- a/mm/debug_vm_pgtable.c~mm-debug_vm_pgtable-ppc64-avoid-setting-top-bits-in-radom-value
+++ a/mm/debug_vm_pgtable.c
@@ -44,10 +44,17 @@ 
  * entry type. But these bits might affect the ability to clear entries with
  * pxx_clear() because of how dynamic page table folding works on s390. So
  * while loading up the entries do not change the lower 4 bits. It does not
- * have affect any other platform.
+ * have affect any other platform. Also avoid the 62nd bit on ppc64 that is
+ * used to mark a pte entry.
  */
-#define S390_MASK_BITS	4
-#define RANDOM_ORVALUE	GENMASK(BITS_PER_LONG - 1, S390_MASK_BITS)
+#define S390_SKIP_MASK		GENMASK(3, 0)
+#if __BITS_PER_LONG == 64
+#define PPC64_SKIP_MASK		GENMASK(62, 62)
+#else
+#define PPC64_SKIP_MASK		0x0
+#endif
+#define ARCH_SKIP_MASK (S390_SKIP_MASK | PPC64_SKIP_MASK)
+#define RANDOM_ORVALUE (GENMASK(BITS_PER_LONG - 1, 0) & ~ARCH_SKIP_MASK)
 #define RANDOM_NZVALUE	GENMASK(7, 0)
 
 static void __init pte_basic_tests(unsigned long pfn, pgprot_t prot)