Re: [PATCH v1 3/3] powerpc/code-patching: Optimise patch_memcpy() to 4 byte chunks

On Fri, 2024-03-15 at 06:39 +0000, Christophe Leroy wrote:

Le 15/03/2024 à 03:57, Benjamin Gray a écrit :

quoted

As we are patching instructions, we can assume the length is a
multiple
of 4 and the destination address is aligned.

Atomicity of patching a prefixed instruction is not a concern, as
the
original implementation doesn't provide it anyway.

This patch looks unnecessary.

copy_to_kernel_nofault() is what you want to use instead.

Yeah, I would drop this patch when using copy_to_kernel_nofault()

quoted

Signed-off-by: Benjamin Gray <redacted>
---
  arch/powerpc/lib/code-patching.c | 8 ++++----
  1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/lib/code-patching.c

b/arch/powerpc/lib/code-patching.c
index c6633759b509..ed450a32918c 100644

--- a/arch/powerpc/lib/code-patching.c
+++ b/arch/powerpc/lib/code-patching.c

@@ -394,10 +394,10 @@ static int patch_memset32(u32 *addr, u32 val,

size_t count)
  	return -EPERM;
  }
  
-static int patch_memcpy(void *dst, void *src, size_t len)
+static int patch_memcpy32(u32 *dst, u32 *src, size_t count)
  {
-	for (void *end = src + len; src < end; dst++, src++)
-		__put_kernel_nofault(dst, src, u8, failed);
+	for (u32 *end = src + count; src < end; dst++, src++)
+		__put_kernel_nofault(dst, src, u32, failed);
  
  	return 0;
  

@@ -424,7 +424,7 @@ static int __patch_instructions(u32

*patch_addr, u32 *code, size_t len, bool rep
  			err = patch_memset32(patch_addr, val, len
/ 4);
  		}
  	} else {
-		err = patch_memcpy(patch_addr, code, len);
+		err = patch_memcpy32(patch_addr, code, len / 4);
  	}
  
  	smp_wmb();	/* smp write barrier */