Re: [REGRESSION 6.12.90 -> 6.12.94] vsock/virtio: large AF_VSOCK transfers reset under backpressure

[Stefano Garzarella <sgarzare@redhat.com>]

On Mon, Jun 22, 2026 at 07:55:30AM -0400, Brien Oberstein wrote:
>Hi Stefano,
>
>Thanks, that matches what I'm seeing: large transfers reset mid-stream
>instead of the sender being throttled (reliable above ~1.5 MB, fine below
>~90 KB).
>
>The bind for me: it's not just this mail bridge -- I use AF_VSOCK for a few
>host/guest services, some of which open their own sockets, so the per-socket
>buffer workaround can't cover them all. That leaves pinning 6.12.90 (losing
>the DoS fix and further kernel updates) as the only blanket option.

Okay, but in that case did it work?

>
>A few quick questions:
>
>1. Is a -stable backport of the merging fix likely, and roughly when?

We don't have a fix yet.

>2. Could a smaller interim land in -stable sooner (e.g. more default
>   headroom) without reopening the DoS?

What we've merged so far is the best we can do for now, but anyone who 
wants to help improve the situation is welcome to submit patches.

>3. Will the fix guarantee backpressure for any packet size, or just widen
>   the margin?

It should fix STREAM sockets for any packet size.
SEQPACKET/DGRAM is a bit different since we need to keep boundaries, so 
it will come later if needed.

>
>Happy to test any patch

THanks, I'll ask you to test.

>I have a solid reproducer and can turn it around
>in a day. I'll also file this as a tracked regression so it's not lost.

Unfortunately, it's always been partially broken, using more memory than 
specified, so I don't know if this is actually a full regression, but I 
understand.

Thanks,
Stefano