linux-kernel - Re: [PATCH v1 02/14] futex: Extend the FUTEX2 flags

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Message-ID: <20230721185246.GR4253@hirez.programming.kicks-ass.net>
Date:   Fri, 21 Jul 2023 20:52:46 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>, Jens Axboe <axboe@...nel.dk>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Darren Hart <dvhart@...radead.org>, dave@...olabs.net,
        andrealmeid@...lia.com, Andrew Morton <akpm@...ux-foundation.org>,
        urezki@...il.com, Christoph Hellwig <hch@...radead.org>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        linux-api@...r.kernel.org, linux-mm@...ck.org,
        Linux-Arch <linux-arch@...r.kernel.org>, malteskarupke@....de
Subject: Re: [PATCH v1 02/14] futex: Extend the FUTEX2 flags

On Fri, Jul 21, 2023 at 05:47:31PM +0200, Arnd Bergmann wrote:
> On Fri, Jul 21, 2023, at 12:22, Peter Zijlstra wrote:
> >   * futex_parse_waitv - Parse a waitv array from userspace
> > @@ -207,7 +207,12 @@ static int futex_parse_waitv(struct fute
> >  		if ((aux.flags & ~FUTEX2_MASK) || aux.__reserved)
> >  			return -EINVAL;
> > 
> > -		if (!(aux.flags & FUTEX2_32))
> > +		if (!IS_ENABLED(CONFIG_64BIT) || in_compat_syscall()) {
> > +			if ((aux.flags & FUTEX2_64) == FUTEX2_64)
> > +				return -EINVAL;
> > +		}
> > +
> > +		if ((aux.flags & FUTEX2_64) != FUTEX2_32)
> >  			return -EINVAL;
> 
> This looks slightly confusing, how about defining another
> FUTEX2_SIZEMASK (or similar) macro to clarify that
> "aux.flags & FUTEX2_64" is a mask operation that can
> match the FUTEX2_{8,16,32,64} values?

Yeah, I had that in an earlier version, but then reconsidered as I
didn't want to clutter the uabi with that. But perhaps I over-throught
this.