linux-kernel - Re: [PATCH v2 31/32] sh: support a 2-byte smp_store

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: <20160106131321-mutt-send-email-mst@redhat.com>
Date:	Wed, 6 Jan 2016 13:19:44 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Rich Felker <dalias@...c.org>
Cc:	linux-kernel@...r.kernel.org, linux-sh@...r.kernel.org,
	peterz@...radead.org
Subject: Re: [PATCH v2 31/32] sh: support a 2-byte smp_store_mb

On Tue, Jan 05, 2016 at 06:27:35PM -0500, Rich Felker wrote:
> On Thu, Dec 31, 2015 at 09:09:47PM +0200, Michael S. Tsirkin wrote:
> > At the moment, xchg on sh only supports 4 and 1 byte values, so using it
> > from smp_store_mb means attempts to store a 2 byte value using this
> > macro fail.
> > 
> > And happens to be exactly what virtio drivers want to do.
> > 
> > Check size and fall back to a slower, but safe, WRITE_ONCE+smp_mb.
> 
> Can you please do this for size 1 as well (i.e. all sizes != 4)? If
> you check the source, the code for size-1 xchg in sh cmpxchg-llsc.h is
> completely wrong and operates on a 32-bit object at the address passed
> to it. This code is presently unused anyway and I plan to submit a
> patch to remove the size 1 case.
> 
> Rich

Ouch. And PeterZ says I should write a 2-byte xchg in asm instead,
and Fedora can't even build a full kernel for this arch at the moment :(

Peter, what do you think? How about I leave this patch as is for now?

-- 
MST
--
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/