arm64: mm: Complete the PTE store in ptep_try_set()

ptep_try_set() installs a kernel PTE with try_cmpxchg() but, unlike
__set_pte(), skips the barriers that arm64 requires after writing a valid
kernel PTE. Without them a subsequent access can fault instead of seeing
the new mapping.

Issue them with emit_pte_barriers() rather than __set_pte_complete().
ptep_try_set() must finish the store before it returns, but
__set_pte_complete() would defer the barriers when the calling context is in
lazy MMU mode.

v2: Emit the barriers directly instead of __set_pte_complete(). (Catalin)

Fixes: 258df8fce42f ("mm: Add ptep_try_set() for lockless empty-slot installs")
Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/all/aiRFcz78QTZdIHHB@arm.com/
Link: https://lore.kernel.org/bpf/7f5f7c94601312c1a401fb18998291cc@kernel.org
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 3ce0f2a6cab6ab92ae5173bc6e39cd1b3c7b3d86..3e579c26b383c6c98b12ed8f4f1e1082669a9c8e 100644 (file)
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -1838,7 +1838,16 @@ static inline bool ptep_try_set(pte_t *ptep, pte_t new_pte)
 {
        pteval_t old = 0;
 
-       return try_cmpxchg(&pte_val(*ptep), &old, pte_val(new_pte));
+       if (!try_cmpxchg(&pte_val(*ptep), &old, pte_val(new_pte)))
+               return false;
+
+       /*
+        * The store must be complete by the time this returns, but the caller
+        * may be in lazy MMU mode, where __set_pte_complete() would defer the
+        * barriers. Issue them directly.
+        */
+       emit_pte_barriers();
+       return true;
 }
 #define ptep_try_set ptep_try_set