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Mon, 05 Oct 2026 10:38:14 -0700 (PDT) Date: Mon, 5 Oct 2026 10:38:13 -0700 From: Joe Damato To: Eric Dumazet Cc: Stefan Fleischmann , netdev@vger.kernel.org, stable@vger.kernel.org, Michael Chan , Pavan Chebbi , regressions@lists.linux.dev Subject: Re: [REGRESSION] Commit 447cbe95ebb9 causes IOMMU DMA faults on macvlan/vlan with bnxt_en Message-ID: Mail-Followup-To: Joe Damato , Eric Dumazet , Stefan Fleischmann , netdev@vger.kernel.org, stable@vger.kernel.org, Michael Chan , Pavan Chebbi , regressions@lists.linux.dev References: <20261004122616.56714cbd@nargothrond> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Sun, Oct 04, 2026 at 01:46:08PM +0200, Eric Dumazet wrote: > > > On 10/4/26 12:26, Stefan Fleischmann wrote: > > Hi, > > > > I have bisected a regression introduced in kernel 6.18.51 (and 7.2.3). > > The issue is still present in 6.18.55 and 7.2.9. Verified by reverting > > 1517d1996b52 (the equivalent of 447cbe95ebb9 in the 6.18 branch) on top > > of 6.18.51 and 6.18.55. > > > > The hardware is a Dell R640 server with Intel Xeon Silver 4210 and > > Broadcom BCM57412 NetXtreme-E NIC. > > > > The network interface is configured as an untagged interface and has a > > couple of tagged VLAN interfaces configured on top. All of these are > > used by LXC containers with Macvlan. > > > > The interface comes up fine after boot, but after some time (anywhere > > between 2 to 40 minutes) I see a DMA error in the kernel log (attached), > > and the driver ends up tearing down the interface. It can be brought up > > again after that, but it will hit a DMA error again after a while and > > the interface goes down again. > > > > I'm happy to provide more debug info if needed, or test patches. > > Hi Stefan, > > Thanks for the bisect and detailed report. > > Notice that 0xfc499000 is on an exact 4KB page boundary. This points to a > DMA read overrun where the Broadcom DMA engine reads past the end of a > buffer mapped in page 0xfc498xxx into the adjacent unmapped page 0xfc499000. > > Have you tried a recent net kernel ? > > Could you please test whether disabling TSO or hardware VLAN offload > prevents the crash? (maybe adding one option at a time) > > # ethtool -K eno1np0 tso off > > # ethtool -K eno1np0 tx-vlan-offload off > > Adding Joe to this thread, because some parts in > tso_dma_map_init() or tso_start() might have bugs. Thanks for adding me and debugging this. We've been hitting a similar read fault for a very long time I've had trouble tracking down (it's been reproducing since at least kernel 6.9, long before my SW USO changes). In the case I am tracking, it seems to reproduce (fairly rarely) and seems to be caused by a tcpv6 TSO packet with a read fault in the last page of a 32k frag. I have yet to find a reproducer for my issue, though :( I'll try this patch, but IIUC padding only applies to frames under 52 bytes, so I'm not sure if it's the same bug I have been searching for.