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]
Date:	Thu, 04 Oct 2012 09:54:01 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	"Michael S. Tsirkin" <mst@...hat.com>,
	Thomas Lendacky <tahm@...ux.vnet.ibm.com>
Cc:	Sasha Levin <levinsasha928@...il.com>,
	virtualization@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, avi@...hat.com, kvm@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH 2/3] virtio-net: correct capacity math on ring full

"Michael S. Tsirkin" <mst@...hat.com> writes:
> Capacity math on ring full is wrong: we are
> looking at num_sg but that might be optimistic
> because of indirect buffer use.
>
> The implementation also penalizes fast path
> with extra memory accesses for the benefit of
> ring full condition handling which is slow path.
>
> It's easy to query ring capacity so let's do just that.

This path will reduce the actual queue use to worst-case assumptions.
With bufferbloat maybe that's a good thing, but it's true.

If we do this, the code is now wrong:

	/* This can happen with OOM and indirect buffers. */
	if (unlikely(capacity < 0)) {

Because this should now *never* happen.

But I do like the cleanup; returning capacity from add_buf() was always
hacky.  I've got an idea, we'll see what it looks like...

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

Powered by blists - more mailing lists