netdev - Re: [patch 13/26] Xen-paravirt_ops: Consistently wrap paravirt ops callsites to make them patchable

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: <1174348905.11680.54.camel@localhost.localdomain>
Date:	Tue, 20 Mar 2007 11:01:45 +1100
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andi Kleen <ak@....de>, David Miller <davem@...emloft.net>,
	jeremy@...p.org, mingo@...e.hu, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, virtualization@...ts.osdl.org,
	xen-devel@...ts.xensource.com, chrisw@...s-sol.org,
	zach@...are.com, anthony@...emonkey.ws, netdev@...r.kernel.org
Subject: Re: [patch 13/26] Xen-paravirt_ops: Consistently wrap paravirt ops
	callsites to make them patchable

On Mon, 2007-03-19 at 11:38 -0700, Linus Torvalds wrote:
> 
> On Mon, 19 Mar 2007, Eric W. Biederman wrote:
> > 
> > True.  You can use all of the call clobbered registers.
> 
> Quite often, the biggest single win of inlining is not so much the code 
> size (although if done right, that will be smaller too), but the fact that 
> inlining DOES NOT CLOBBER AS MANY REGISTERS!

Thanks Linus.

*This* was the reason that the current hand-coded calls only clobber %
eax.  It was a compromise between native (no clobbers) and others (might
need a reg).

Now, since we decided to allow paravirt_ops operations to be normal C
(ie. the patching is optional and done late), we actually push and pop %
ecx and %edx.  This makes the call site 10 bytes long, which is a nice
size for patching anyway (enough for a movl $0, <addr>, a-la lguest's
cli, or movw $0, %gs:<addr> if we supported SMP).

The current 6 paravirt ops which are patched cover the vast majority of
calls (until the Xen patches, then we need ~4 more?).  Jeremy chose to
expand patching to cover *all* paravirt ops, rather than just the new
hot ones, and that's where we tipped over the ugliness threshold.

Cheers,
Rusty.

-
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html