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-rw-r--r--arch/arm64/mm/fault.c15
1 files changed, 8 insertions, 7 deletions
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index c7861c9864e6..2509e4fe6992 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -163,26 +163,27 @@ int ptep_set_access_flags(struct vm_area_struct *vma,
/* only preserve the access flags and write permission */
pte_val(entry) &= PTE_AF | PTE_WRITE | PTE_DIRTY;
- /*
- * PTE_RDONLY is cleared by default in the asm below, so set it in
- * back if necessary (read-only or clean PTE).
- */
+ /* set PTE_RDONLY if actual read-only or clean PTE */
if (!pte_write(entry) || !pte_sw_dirty(entry))
pte_val(entry) |= PTE_RDONLY;
/*
* Setting the flags must be done atomically to avoid racing with the
- * hardware update of the access/dirty state.
+ * hardware update of the access/dirty state. The PTE_RDONLY bit must
+ * be set to the most permissive (lowest value) of *ptep and entry
+ * (calculated as: a & b == ~(~a | ~b)).
*/
+ pte_val(entry) ^= PTE_RDONLY;
asm volatile("// ptep_set_access_flags\n"
" prfm pstl1strm, %2\n"
"1: ldxr %0, %2\n"
- " and %0, %0, %3 // clear PTE_RDONLY\n"
+ " eor %0, %0, %3 // negate PTE_RDONLY in *ptep\n"
" orr %0, %0, %4 // set flags\n"
+ " eor %0, %0, %3 // negate final PTE_RDONLY\n"
" stxr %w1, %0, %2\n"
" cbnz %w1, 1b\n"
: "=&r" (old_pteval), "=&r" (tmp), "+Q" (pte_val(*ptep))
- : "L" (~PTE_RDONLY), "r" (pte_val(entry)));
+ : "L" (PTE_RDONLY), "r" (pte_val(entry)));
flush_tlb_fix_spurious_fault(vma, address);
return 1;