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  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]
Date:	Tue, 11 Mar 2014 00:30:01 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	linux-kernel@...r.kernel.org, jbenc@...hat.com,
	David Miller <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Daniel Borkmann <dborkman@...hat.com>,
	Simon Horman <horms@...ge.net.au>,
	Paul Durrant <Paul.Durrant@...rix.com>,
	Thomas Graf <tgraf@...g.ch>, Miklos Szeredi <mszeredi@...e.cz>,
	=?UTF-8?q?Peter=20Pan=28=E6=BD=98=E5=8D=AB=E5=B9=B3=29?= <panweiping3@...il.com>,
	netdev@...r.kernel.org
Subject: Re: [PATCH 5/5] skbuff: skb_segment: orphan frags before copying

On Tue, Mar 11, 2014 at 06:12:23AM +0800, Herbert Xu wrote:
> On Tue, Mar 11, 2014 at 12:07:17AM +0200, Michael S. Tsirkin wrote:
> > 
> > Once one skb completes the callback is invoked and userspace
> > reuses this buffer for something else.
> > At that point it's too late to do the copy.
> 
> OK, would it be possible to delay the callback until all generated
> skbs are completed?

Hmm this won't be easy since devices can complete them in any order.
See below for some ideas.

> > > IOW if we pass along SKBTX_SHARED_FRAG will it work?
> > 
> > I don't see how would SKBTX_SHARED_FRAG help with this at all.
> > That only works for pages gifted to kernel by e.g. vmsplice
> > that aren't reused by userspace.
> 
> Sorry cut-n-paste error, I meant SKBTX_DEV_ZEROCOPY.
> 
> Cheers,

Ah ok. Well we'd need to reference-count them somehow.
Maybe skb_get and stick the pointer in ubuf callback for the
new skbs, make ubuf callback kfree_skb?
Not sure if that's too much memory ...

I also worry a bit that we'll lose the success flag value which is used
to disable zero copy on OOM errors more aggressively.

How about we do the simple thing as the first step and try to optimize
as a separate patch on top?

> -- 
> Email: Herbert Xu <herbert@...dor.apana.org.au>
> Home Page: http://gondor.apana.org.au/~herbert/
> PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
--
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/

Powered by blists - more mailing lists