linux-kernel - Re: [patch 5/8] Immediate Values - x86 Optimization (simplified)

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20071120170222.GB31044@Krystal>
Date:	Tue, 20 Nov 2007 12:02:22 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Andi Kleen <ak@....de>, "H. Peter Anvin" <hpa@...or.com>,
	Chuck Ebbert <cebbert@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch 5/8] Immediate Values - x86 Optimization (simplified)

* Rusty Russell (rusty@...tcorp.com.au) wrote:
> On Tuesday 20 November 2007 01:28:03 Mathieu Desnoyers wrote:
> > * Rusty Russell (rusty@...tcorp.com.au) wrote:
> > > I think it would be easier to just fast-path the num_online_cpus == 1
> > > case, even if you want to keep this "update_early" interface.
> >
> > Nope, that could lead to problems. I call core_immediate_update()
> > _very_ early, before boot_cpu_init() is called.
> 
> Ah, I see the problem.  It would in fact be clearer for us to move 
> boot_cpu_init() up to just after smp_setup_processor_id() in start_kernel 
> anyway, not just for this code, but in general.
> 

Could be done.

> > Therefore, 
> > cpu_online_map is not set yet. I am not sure the benefit of using
> > num_online_cpus outweights the added fragility wrt other boot process
> > initializations.
> 
> I think it's still a win, though worth a comment that we always go via the 
> non-IPI path for the early boot case.
> 

Ok, another potential problem then :

If we fast-path the num_online_cpus == 1, then updates done after the
boot process will have to go through this code. Therefore, we would have
to disable interrupts in the early boot code.

However, I doubt it is safe to use the paravirtualized
local_irq_disable/enable before the paravirt code is executed ?

Mathieu

> Cheers,
> Rusty.

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/