netdev - Re: [PATCH net] virtio-net: reject small vring sizes

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Message-ID: <AM0PR04MB4723FA90465186B5A8A5C001D4669@AM0PR04MB4723.eurprd04.prod.outlook.com>
Date:   Sun, 23 Apr 2023 06:51:46 +0000
From:   Alvaro Karsz <alvaro.karsz@...id-run.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
CC:     Jason Wang <jasowang@...hat.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net] virtio-net: reject small vring sizes

> Yes that makes sense, it's architetural. We can disable ctrl vq though.

The problem here is that we know the vring size after calling virtnet_find_vqs, so the number of VQs already includes the control VQ.

Actually, many variables/settings that are initialized before we call virtnet_find_vqs may need modifications if we use small vrings.
For example has_rss_hash_report, has_rss, hdr_len etc..

We could have a fixup function to fix everything after we discover that we are using small vrings, but, honestly, I think that this will be hard to maintain in the future, and I don't like this approach much.

The ideal thing will be to discover if we use small vrings in probe's beginning.

I'm looking for a way at the moment.