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

[Benjamin Gray <bgray@linux.ibm.com>]

On Fri, 2024-03-15 at 06:39 +0000, Christophe Leroy wrote:
> 
> 
> Le 15/03/2024 à 03:57, Benjamin Gray a écrit :
> > 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()

> 
> > 
> > Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
> > ---
> >   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 */