Re: [PATCH v2 1/5] arm64: kasan: allow to init memory when setting tags

On Mon, Mar 8, 2021 at 5:58 PM Catalin Marinas [off-list ref] wrote:

On Mon, Mar 08, 2021 at 04:55:14PM +0100, Andrey Konovalov wrote:

quoted

@@ -68,10 +69,16 @@ static inline void mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
               * 'asm volatile' is required to prevent the compiler to move
               * the statement outside of the loop.
               */
-             asm volatile(__MTE_PREAMBLE "stg %0, [%0]"
-                          :
-                          : "r" (curr)
-                          : "memory");
+             if (init)
+                     asm volatile(__MTE_PREAMBLE "stzg %0, [%0]"
+                                  :
+                                  : "r" (curr)
+                                  : "memory");
+             else
+                     asm volatile(__MTE_PREAMBLE "stg %0, [%0]"
+                                  :
+                                  : "r" (curr)
+                                  : "memory");

              curr += MTE_GRANULE_SIZE;
      } while (curr != end);

Is 'init' always a built-in constant here? If not, checking it once
outside the loop may be better (or check the code generation, maybe the
compiler is smart enough).

I think it's worth moving the init check outside the loop anyway. Will do in v3.

Thanks!

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