arm64: Update PTE_RDONLY in set_pte_at() for PROT_NONE permission

The set_pte_at() function must update the hardware PTE_RDONLY bit
depending on the state of the PTE_WRITE and PTE_DIRTY bits of the given
entry value. However, it currently only performs this for pte_valid()
entries, ignoring PTE_PROT_NONE. The side-effect is that PROT_NONE
mappings would not have the PTE_RDONLY bit set. Without
CONFIG_ARM64_HW_AFDBM, this is not an issue since such PROT_NONE pages
are not accessible anyway.

With commit 2f4b829c625e ("arm64: Add support for hardware updates of
the access and dirty pte bits"), the ptep_set_wrprotect() function was
re-written to cope with automatic hardware updates of the dirty state.
As an optimisation, only PTE_RDONLY is checked to assess the "dirty"
status. Since set_pte_at() does not set this bit for PROT_NONE mappings,
such pages may be considered "dirty" as a result of
ptep_set_wrprotect().

This patch updates the pte_valid() check to pte_present() in
set_pte_at(). It also adds PTE_PROT_NONE to the swap entry bits comment.

Fixes: 2f4b829c625e ("arm64: Add support for hardware updates of the access and dirty pte bits")
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Reported-by: Ganapatrao Kulkarni <gkulkarni@caviumnetworks.com>
Tested-by: Ganapatrao Kulkarni <gkulkarni@cavium.com>
Cc: <stable@vger.kernel.org>

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 7c73b36..e308807 100644 (file)
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -201,7 +201,7 @@ extern void __sync_icache_dcache(pte_t pteval, unsigned long addr);
 static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
                              pte_t *ptep, pte_t pte)
 {
-       if (pte_valid(pte)) {
+       if (pte_present(pte)) {
                if (pte_sw_dirty(pte) && pte_write(pte))
                        pte_val(pte) &= ~PTE_RDONLY;
                else
@@ -626,6 +626,7 @@ extern pgd_t idmap_pg_dir[PTRS_PER_PGD];
  *     bits 0-1:       present (must be zero)
  *     bits 2-7:       swap type
  *     bits 8-57:      swap offset
+ *     bit  58:        PTE_PROT_NONE (must be zero)
  */
 #define __SWP_TYPE_SHIFT       2
 #define __SWP_TYPE_BITS                6