netdev - Re: [PATCH v2] net: filter: BPF 'JIT' compiler for PPC64

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Message-ID: <1311066368.2375.13.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC>
Date:	Tue, 19 Jul 2011 11:06:08 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Matt Evans <matt@...abs.org>, netdev@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2] net: filter: BPF 'JIT' compiler for PPC64

Le mardi 19 juillet 2011 à 17:55 +1000, Benjamin Herrenschmidt a écrit :
> On Tue, 2011-07-19 at 08:51 +0200, Eric Dumazet wrote:
> 
> > > +		case BPF_S_ANC_CPU:
> > > +#ifdef CONFIG_SMP
> > > +			/*
> > > +			 * PACA ptr is r13:
> > > +			 * raw_smp_processor_id() = local_paca->paca_index
> > > +			 */
> > 
> > This could break if one day linux supports more than 65536 cpus :)
> > 
> > > +			PPC_LHZ_OFFS(r_A, 13,
> > > +				     offsetof(struct paca_struct, paca_index));
> > > +#else
> > > +			PPC_LI(r_A, 0);
> > > +#endif
> > > +			break;
> 
> As would our implementation of raw_smp_processor_id() and our
> spinlocks :-) I don't think we need to fix that -now- but you are
> welcome to add something like a
> BUILD_BUG_ON(sizeof(local_paca->paca_index) != 2); as a reminder :-)

Please Matt add to your next version this check. I dont think I have to
submit a one line patch later...

On x86_64, cpu_number field is already 32bit, we have some time before
it becomes 64bit ;)

We probably should add some extra check to make sure segment doesnt
change (%gs on x86_64, r13 on ppc64) on a future linux version.



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