Re: [PATCH rc v7 0/7] iommu/arm-smmu-v3: Fix device crash on kdump kernel

[Nicolin Chen]

On Thu, Jul 02, 2026 at 08:50:04PM -0300, Jason Gunthorpe wrote:
> On Thu, Jul 02, 2026 at 12:25:43PM -0700, Nicolin Chen wrote:
> > On Thu, Jul 02, 2026 at 11:41:57AM -0300, Jason Gunthorpe wrote:
> > > The VMIDs that are in-used by the adopted stream table have to be
> > > removed from the idr as well (and similarly for ASID if we don't have
> > > VMID HW support).
> > > 
> > > Then the VMIDs that may be dirtied by the prior kernel remain isolated
> > > and are never re-used by the new kernel. When the new kernel wants to
> > > do DMA it will replace the STE with a new, clean VMID, and there is no
> > > problem.
> > 
> > I see. I assume the reserved VMID for the kdump kernel will be a
> > clean VMID (!=0). That should guarantee different cache tags.
> 
> You will also have to change things to allocate the kernel global vmid
> from the IDR, it will usually be 0 but not for kdump. Then you have to
> find all the places where the 0 is implicitly placed and put in the
> actual value.

Hmm, I just realized that all the EL2 commands do not take VMID.

Looks like we have no choice but to scan through all the CDs for
the ASID too..

Nicolin