Re: [PATCH 10/13] powerpc/rtas: improve function information lookups

From: Andrew Donnellan <ajd@linux.ibm.com>
To: Nick Child <nnac123@linux.ibm.com>,
	Nathan Lynch <nathanl@linux.ibm.com>,
	linuxppc-dev@lists.ozlabs.org
Cc: tyreld@linux.ibm.com, ldufour@linux.ibm.com, npiggin@gmail.com
Subject: Re: [PATCH 10/13] powerpc/rtas: improve function information lookups
Date: Thu, 24 Nov 2022 14:28:30 +1100	[thread overview]
Message-ID: <2ba2809a545d0f84b336f78baf2dbe2ff20dc105.camel@linux.ibm.com> (raw)
In-Reply-To: <c183a039-2001-eb3a-7028-f8a0813987cf@linux.ibm.com>

On Wed, 2022-11-23 at 13:32 -0600, Nick Child wrote:
> On 11/22/22 20:51, Andrew Donnellan wrote:
> > On Fri, 2022-11-18 at 09:07 -0600, Nathan Lynch wrote:
> > > +enum rtas_function_flags {
> > > +       RTAS_FN_FLAG_BANNED_FOR_SYSCALL_ON_LE = (1 << 0),
> > > +};
> > 
> > This seems to be new, what's the justification?
> > 
> 
> Seems to be a run-time replacement of:
> #ifdef CONFIG_CPU_BIG_ENDIAN
>         { "ibm,suspend-me", -1, -1, -1, -1, -1 },
>         { "ibm,update-nodes", -1, 0, -1, -1, -1, 4096 },
>         { "ibm,update-properties", -1, 0, -1, -1, -1, 4096 },
> #endif
> 
> It looks to be handled logically:
> + if (IS_ENABLED(CONFIG_CPU_LITTLE_ENDIAN) &&
> +           (func->flags & RTAS_FN_FLAG_BANNED_FOR_SYSCALL_ON_LE))
> +               goto err;
> 
> Perhaps, also allow the addition of any future special cases
> for rtas functions easier to maintain?

Makes sense, though I'm slightly confused about the original rationale
for the ifdef and why it's not being fixed in userspace.

Slightly clunky name though, something like
RTAS_FN_FLAG_SYSCALL_BE_ONLY might be less clunky?

-- 
Andrew Donnellan    OzLabs, ADL Canberra
ajd@linux.ibm.com   IBM Australia Limited