Re: [Intel-wired-lan] [RFC PATCHv2 1/1] idpf: Fix header clobber in IDPF with SWIOTLB enabled

Steve Rutherford via Intel-wired-lan
2026-03-06T19:36:11Z

On Fri, Mar 6, 2026 at 6:52 AM Alexander Lobakin
<aleksander.lobakin@intel.com> wrote:
>
> From: Steve Rutherford <srutherford@google.com>
> Date: Wed, 4 Mar 2026 14:01:46 -0800
>
> > I believe syncing twice isn't inherently wrong - it's more that you
> > can't synthesize the header via the workaround and then sync, since it
> > will pull the uninitialized header buffer from the SWIOTLB. Outside of
> > SWIOTLB, dma syncs are more or less no-ops, while (with SWIOTLB) they
> > are copies from/to the bounce buffers.
>
> Ah I see.
>
> What if I add sync_for_device after copying the header? This should
> synchronize the bounce buffer with the copied data I guess? A bit of
> overhead, but this W/A triggers mostly on stuff like ARP/ICMP, "hotpath"
> L4 protos are fortunately not affected.

That should work fine as well. I'm not certain I have strong
preferences on the right answer here, other than "does it work and,
ideally, is it less confusing?" The patch I posted is a bit
unintuitive. I think what you are describing might make the workaround
self-contained.

thanks,
Steve
[And sorry for my gmail-driven top posting crimes D: ]