Re: [PATCH v4 1/2] hw/i386/amd_iommu: Isolate AMDVI-PCI from amd-iommu device to allow full control over the PCI device creation

["Daniel P. Berrangé" <berrange@redhat.com>]

On Tue, Mar 04, 2025 at 02:17:15PM +0000, Suravee Suthikulpanit wrote:
> Current amd-iommu model internally creates an AMDVI-PCI device. Here is
> a snippet from info qtree:
> 
>   bus: main-system-bus
>     type System
>     dev: amd-iommu, id ""
>       xtsup = false
>       pci-id = ""
>       intremap = "on"
>       device-iotlb = false
>       pt = true
>     ...
>     dev: q35-pcihost, id ""
>       MCFG = -1 (0xffffffffffffffff)
>       pci-hole64-size = 34359738368 (32 GiB)
>       below-4g-mem-size = 134217728 (128 MiB)
>       above-4g-mem-size = 0 (0 B)
>       smm-ranges = true
>       x-pci-hole64-fix = true
>       x-config-reg-migration-enabled = true
>       bypass-iommu = false
>       bus: pcie.0
>         type PCIE
>         dev: AMDVI-PCI, id ""
>           addr = 01.0
>           romfile = ""
>           romsize = 4294967295 (0xffffffff)
>           rombar = -1 (0xffffffffffffffff)
>           multifunction = false
>           x-pcie-lnksta-dllla = true
>           x-pcie-extcap-init = true
>           failover_pair_id = ""
>           acpi-index = 0 (0x0)
>           x-pcie-err-unc-mask = true
>           x-pcie-ari-nextfn-1 = false
>           x-max-bounce-buffer-size = 4096 (4 KiB)
>           x-pcie-ext-tag = true
>           busnr = 0 (0x0)
>           class Class 0806, addr 00:01.0, pci id 1022:0000 (sub 1af4:1100)
>     ...
> 
> This prohibits users from specifying the PCI topology for the amd-iommu device,
> which becomes a problem when trying to support VM migration since it does not
> guarantee the same enumeration of AMD IOMMU device.
> 
> Therfore, decouple the AMDVI-PCI from amd-iommu device and introduce pci-id
> parameter to link between the two devices.

Suggest slightly rewording to make it clear this new approach is opt-in:

 Therefore, allow the 'AMDVI-PCI' device to optionally be pre-created and
 associated with a 'amd-iommu' device via a new 'pci-id' parameter on the
 latter.

> 
> For example:
>   -device AMDVI-PCI,id=iommupci0,bus=pcie.0,addr=0x05 \
>   -device amd-iommu,intremap=on,pt=on,xtsup=on,pci-id=iommupci0 \
> 
> For backward-compatibility, internally create the AMDVI-PCI device if not
> specified on the CLI.
> 
> Co-developed-by: Daniel P. Berrangé <berrange@redhat.com>
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
> ---
>  hw/i386/acpi-build.c |  8 +++----
>  hw/i386/amd_iommu.c  | 52 +++++++++++++++++++++++++++-----------------
>  hw/i386/amd_iommu.h  |  3 ++-
>  3 files changed, 38 insertions(+), 25 deletions(-)

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>


With regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|