powerpc/mm/books3s: Add new pte bit to mark pte temporarily invalid.

BugLink: https://bugs.launchpad.net/bugs/1792195
When splitting a huge pmd pte, we need to mark the pmd entry invalid. We
can do that by clearing _PAGE_PRESENT bit. But then that will be taken as a
swap pte. In order to differentiate between the two use a software pte bit
when invalidating.

For regular pte, due to bd5050e38aec ("powerpc/mm/radix: Change pte relax
sequence to handle nest MMU hang") we need to mark the pte entry invalid when
relaxing access permission. Instead of marking pte_none which can result in
different page table walk routines possibly skipping this pte entry, invalidate
it but still keep it marked present.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
(cherry picked from commit bd0dbb73e01306a1060e56f81e5fe287be936477)
Signed-off-by: Joseph Salisbury <joseph.salisbury@canonical.com>
Acked-by: Khalid Elmously <khalid.elmously@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
index bddf18ad555ff0f1f6381ed5791dcae30a8855fe..7ca3ed05b504d4b97a9392b784b37f48e7afd934 100644 (file)
--- a/arch/powerpc/include/asm/book3s/64/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
@@ -42,6 +42,16 @@
 
 #define _PAGE_PTE              0x4000000000000000UL    /* distinguishes PTEs from pointers */
 #define _PAGE_PRESENT          0x8000000000000000UL    /* pte contains a translation */
+/*
+ * We need to mark a pmd pte invalid while splitting. We can do that by clearing
+ * the _PAGE_PRESENT bit. But then that will be taken as a swap pte. In order to
+ * differentiate between two use a SW field when invalidating.
+ *
+ * We do that temporary invalidate for regular pte entry in ptep_set_access_flags
+ *
+ * This is used only when _PAGE_PRESENT is cleared.
+ */
+#define _PAGE_INVALID          _RPAGE_SW0
 
 /*
  * Top and bottom bits of RPN which can be used by hash
@@ -544,7 +554,13 @@ static inline pte_t pte_clear_savedwrite(pte_t pte)
 
 static inline int pte_present(pte_t pte)
 {
-       return !!(pte_raw(pte) & cpu_to_be64(_PAGE_PRESENT));
+       /*
+        * A pte is considerent present if _PAGE_PRESENT is set.
+        * We also need to consider the pte present which is marked
+        * invalid during ptep_set_access_flags. Hence we look for _PAGE_INVALID
+        * if we find _PAGE_PRESENT cleared.
+        */
+       return !!(pte_raw(pte) & cpu_to_be64(_PAGE_PRESENT | _PAGE_INVALID));
 }
 /*
  * Conversion functions: convert a page and protection to a page entry,