Re: [PATCH v6 01/10] powerpc/uaccess: Add unsafe_copy_from_user

["Christopher M. Riedl" <cmr@codefail.de>]

On Tue Feb 23, 2021 at 11:15 AM CST, Christophe Leroy wrote:
>
>
> Le 21/02/2021 à 02:23, Christopher M. Riedl a écrit :
> > Just wrap __copy_tofrom_user() for the usual 'unsafe' pattern which
> > accepts a label to goto on error.
> > 
> > Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
> > Reviewed-by: Daniel Axtens <dja@axtens.net>
> > ---
> >   arch/powerpc/include/asm/uaccess.h | 3 +++
> >   1 file changed, 3 insertions(+)
> > 
> > diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
> > index 78e2a3990eab..33b2de642120 100644
> > --- a/arch/powerpc/include/asm/uaccess.h
> > +++ b/arch/powerpc/include/asm/uaccess.h
> > @@ -487,6 +487,9 @@ user_write_access_begin(const void __user *ptr, size_t len)
> >   #define unsafe_put_user(x, p, e) \
> >   	__unsafe_put_user_goto((__typeof__(*(p)))(x), (p), sizeof(*(p)), e)
> >   
> > +#define unsafe_copy_from_user(d, s, l, e) \
> > +	unsafe_op_wrap(__copy_tofrom_user((__force void __user *)d, s, l), e)
> > +
>
> Could we perform same as unsafe_copy_to_user() instead of calling an
> external function which is
> banned in principle inside uaccess blocks ?

Yup, with your patch to move the barrier_nospec() into the allowance
helpers this makes sense now. I just tried it and performance does not
change significantly w/ either radix or hash translation. I will include
this change in the next spin - thanks!

>
>
> >   #define unsafe_copy_to_user(d, s, l, e) \
> >   do {									\
> >   	u8 __user *_dst = (u8 __user *)(d);				\
> >