Re: [PATCH 0/2] iommu/arm-smmu-v3: SMMU hitting kdump mid-air

[Breno Leitao <leitao@debian.org>]

On Fri, Sep 11, 2026 at 03:31:28PM -0700, Nicolin Chen wrote:
> On Fri, Sep 11, 2026 at 07:54:43AM -0700, Breno Leitao wrote:
> > My lovely robot and I came with two patches that solved the problem,
> > from a practical perspective and I want to share what has been tested.
> > 
> > Patch 1 carries the previous kernel's L1 descriptors into the new KDUMP table, so
> > those streams keep translating.
> > 
> > Patch 2 stops the core discarding that again: iommu_dma_init() already
> > enables deferred attach for a capture kernel, but the core only honours
> > it for drivers implementing .is_attach_deferred, which until now meant
> > amd and intel. Without it iommu_setup_default_domain() attaches
> > a default domain at probe and the fault returns as F_TRANSLATION.
> > 
> > The x86 IOMMU drivers solve the same/similar problem the same way; see
> > commit 38e5f33ee3596 ("iommu/amd: Reuse device table for kdump").
> 
> This looks like my bigger series:
> https://lore.kernel.org/linux-iommu/cover.1788130528.git.nicolinc@nvidia.com/
> 
> Would you please help check/test?

Tested, and it fixes the problem on Meta kdump kernel. Thanks for the message.
I am dropping my two patches in favour of your series.

Test it on AWS Graviton EC2 metal, 96 cores, two ENA NICs at
0003:2c:00.0 and 0003:2d:00.0. When the kernel crashes the NICs keep
bus-mastering, and the capture kernel builds a stream table with no L1
descriptor for the ENA's StreamID 0x32d00, so that DMA raises
C_BAD_STREAMID. 

Patch 11 is what makes the difference for us. "SMMU currently enabled!
Resetting..." opens every failed capture boot we have on record, and it
does not appear at all with your series applied.

Tested-by: Breno Leitao <leitao@kernel.org>