Re: [PATCH v3 20/22] iommu/amd: Reserve translate-device-id for PCI requestor aliases

[Suthikulpanit, Suravee]

On 7/7/2026 9:39 PM, Jason Gunthorpe wrote:
> On Mon, Jun 29, 2026 at 03:35:33PM +0000, Suravee Suthikulpanit wrote:
> > The per-segment translate-device-id (trans_devid) pool hands out numeric
> > device-table indices used by the AMD vIOMMU / iommufd path (e.g. mapping a
> > KVM file descriptor to a shared trans_devid).
>
> Nothing to do with kvm

Noted. I'll update this in v4.

> > Introduce amd_iommu_trans_devid_reserve_pci_aliases() in trans_devid.c and
> > invoke it from amd_iommu_attach_device() immediately after the primary
> > amd_iommu_trans_devid_reserve() succeeds.  For PCI devices the helper
> > reserves the IVRS alias when it differs from the device BDF, then walks
> > pci_for_each_dma_alias() and reserves each alias BDF.  Repeated attach and
> > overlap with the primary BDF in the PCI walk are handled by the existing
> > idempotency of amd_iommu_trans_devid_reserve() (a second reserve of an
> > already-reserved id succeeds).
>
> It would be so nice if the AMD driver could get fixed up to work more
> like ARM with the alais devids.
>
> ie on probe you allocate an array of all the alias dev ids, fill it in
> with the information from PCI and then never touch the PCI again.
>
> Then you'd just dump the whole array into the allocator in one clean
> shot and this would all be simpler.
>
> Instead we have these endless pci walks every where :\
>
> But its fine like this I suppose

I agree. Let me look into this in following this series, and propose change.

Thanks,
Suravee