Re: [PATCH RESEND v3 6/6] powerpc/signal: Use unsafe_copy_siginfo_to_user()

[Christophe Leroy]

Le 13/09/2021 à 18:21, Eric W. Biederman a écrit :
> ebiederm@xxxxxxxxxxxx (Eric W. Biederman) writes:
>
> > Christophe Leroy <christophe.leroy@xxxxxxxxxx> writes:
> >
> > > Use unsafe_copy_siginfo_to_user() in order to do the copy
> > > within the user access block.
> > >
> > > On an mpc 8321 (book3s/32) the improvment is about 5% on a process
> > > sending a signal to itself.
>
> If you can't make function calls from an unsafe macro there is another
> way to handle this that doesn't require everything to be inline.
>
>  From a safety perspective it is probably even a better approach.

Yes but that's exactly what I wanted to avoid for the native ppc32 case: 
this double hop means useless pressure on the cache. The siginfo_t 
structure is 128 bytes large, that means 8 lines of cache on powerpc 8xx.

But maybe it is acceptable to do that only for the compat case. Let me 
think about it, it might be quite easy.

Christophe