linux-kernel - Re: LFENCE instruction (was: [rfc][patch 3/3] x86: optimise barriers)

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

Message-ID: <20071017122842.GB14401@wotan.suse.de>
Date:	Wed, 17 Oct 2007 14:28:42 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	mikulas@...ax.karlin.mff.cuni.cz, arjan@...radead.org,
	linux-kernel@...r.kernel.org,
	virtualization <virtualization@...ts.linux-foundation.org>
Subject: Re: LFENCE instruction (was: [rfc][patch 3/3] x86: optimise barriers)

On Wed, Oct 17, 2007 at 01:51:17PM +0800, Herbert Xu wrote:
> Nick Piggin <npiggin@...e.de> wrote:
> >
> > Also, for non-wb memory. I don't think the Intel document referenced
> > says anything about this, but the AMD document says that loads can pass
> > loads (page 8, rule b).
> > 
> > This is why our rmb() is still an lfence.
> 
> BTW, Xen (in particular, the code in drivers/xen) uses mb/rmb/wmb
> instead of smp_mb/smp_rmb/smp_wmb when it accesses memory that's
> shared with other Xen domains or the hypervisor.
> 
> The reason this is necessary is because even if a Xen domain is
> UP the hypervisor might be SMP.
> 
> It would be nice if we can have these adopt the new SMP barriers
> on x86 instead of the IO ones as they currently do.

That's a good point actually. Something like raw_smp_*mb, which
always orders memory, but only for regular WB operatoins. I could
put that on the todo list...

-
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/