netdev - Re: [PATCH] virtio_net: Revert "virtio_net: set the default max ring size by find

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: <20220815214604.x7g342h3oadruxx2@awork3.anarazel.de>
Date:   Mon, 15 Aug 2022 14:46:04 -0700
From:   Andres Freund <andres@...razel.de>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Guenter Roeck <linux@...ck-us.net>, linux-kernel@...r.kernel.org,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
        Jason Wang <jasowang@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jens Axboe <axboe@...nel.dk>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Greg KH <gregkh@...uxfoundation.org>, c@...hat.com
Subject: Re: [PATCH] virtio_net: Revert "virtio_net: set the default max ring
 size by find_vqs()"

Hi,

On 2022-08-15 17:39:08 -0400, Michael S. Tsirkin wrote:
> On Mon, Aug 15, 2022 at 02:28:39PM -0700, Andres Freund wrote:
> > On 2022-08-15 17:04:10 -0400, Michael S. Tsirkin wrote:
> > > So virtio has a queue_size register. When read, it will give you
> > > originally the maximum queue size. Normally we just read it and
> > > use it as queue size.
> > > 
> > > However, when queue memory allocation fails, and unconditionally with a
> > > network device with the problematic patch, driver is asking the
> > > hypervisor to make the ring smaller by writing a smaller value into this
> > > register.
> > > 
> > > I suspect that what happens is hypervisor still uses the original value
> > > somewhere.
> > 
> > It looks more like the host is never told about the changed size for legacy
> > devices...
> > 
> > Indeed, adding a vp_legacy_set_queue_size() & call to it to setup_vq(), makes
> > 5.19 + restricting queue sizes to 1024 boot again.
> 
> Interesting, the register is RO in the legacy interface.
> And to be frank I can't find where is vp_legacy_set_queue_size
> even implemented. It's midnight here too ...

Yea, I meant that added both vp_legacy_set_queue_size() and a call to it. I
was just quickly experimenting around.


> Yes I figured this out too. And I was able to reproduce on qemu now.

Cool.


> I'm posting a new patchset reverting all the handing of resize
> restrictions, I think we should rethink it for the next release.

Makes sense.

Greetings,

Andres Freund