Re: [PATCH 0/5] Add support for user creatable SMMUv3 device

[Donald Dutile <ddutile@redhat.com>]

Shameer,
Hi!

First off, like the partitioning of these pieces.

On 4/15/25 4:10 AM, Shameer Kolothum wrote:
> Hi All,
> 
> This patch series introduces support for a user-creatable SMMUv3 device
> (-device arm-smmuv3-dev) in QEMU.
> 
Can we drop the '-dev', as 'arm-smmu' is sufficient, as is '-device'?

I know, internal to QEMU, there's already an ARM_SMMU, but as suggested later,
if it uses the same struct, the qemu cmdline syntax is a bit less redundant.

> The implementation is based on feedback received from the RFCv2[0]:
> "hw/arm/virt: Add support for user-creatable accelerated SMMUv3"
> 
> Currently, QEMU's SMMUv3 emulation (iommu=smmuv3) is tied to the machine
> and does not support instantiating multiple SMMUv3 devices—each associated
> with a separate PCIe root complex. In contrast, real-world ARM systems
> often include multiple SMMUv3 instances, each bound to a different PCIe
> root complex.
> 
> This also lays the groundwork for supporting accelerated SMMUv3, as
> proposed in the aforementioned RFC. Please note, the accelerated SMMUv3
> support is not part of this series and will be sent out as a separate
> series later on top of this one.
> 
> Summary of changes:
> 
>   -Introduces support for multiple -device arm-smmuv3-dev,bus=pcie.x
>    instances.
> 
>    Example usage:
> 
>    -device arm-smmuv3-dev,bus=pcie.0
>    -device virtio-net-pci,bus=pcie.0
>    -device pxb-pcie,id=pcie.1,bus_nr=2
>    -device arm-smmuv3-dev,bus=pcie.1
>    -device pcie-root-port,id=pcie.port1,bus=pcie.1
>    -device virtio-net-pci,bus=pcie.port1
> 
>    -Supports either the legacy iommu=smmuv3 option or the new
>    "-device arm-smmuv3-dev" model.
> 
nice! :)
Can it support both? i.e., some devices using a system-wide, legacy smmuv3,
and some pcie devices using the -device arm-smmuv3 ?

If not, then add a check to min-warn or max-fail, that config.
I can see old machines being converted/upgraded to new machines,
and they will want to switch from legacy->device smmuv3, and catching
an edit/update to a machine change (or enabling automated conversion) would be helpful.

>    -Adds device tree bindings for the new SMMUv3 device on the arm/virt
>     machine only, and only for the default pcie.0 root complex.
>     (Note: pxb-pcie root complexes are currently not supported with the
>      device tree due to known limitations[1].)
>    -Restricts usage of the new SMMUv3 device to virt machine versions > 9.2.
>     This is to avoid creating new smmuv3 device for old virt machine versions
>     and accidently breaking the migration support.
> 
> Please take a look and let me know your feedback.
> 
> Thanks,
> Shameer
> [0]:https://lore.kernel.org/qemu-devel/20250311141045.66620-1-shameerali.kolothum.thodi@huawei.com/
> [1]:https://lore.kernel.org/qemu-devel/20230421165037.2506-1-Jonathan.Cameron@huawei.com/
> 
> Shameer Kolothum (5):
>    hw/arm/smmuv3: Introduce SMMUv3 device
>    hw/arm/virt-acpi-build: Update IORT for multiple smmuv3 devices
>    hw/arm/virt: Factor out common SMMUV3 dt bindings code
>    hw/arm/virt: Add support for smmuv3 device
>    hw/arm/smmuv3: Enable smmuv3 device creation
> 
>   hw/arm/smmuv3.c          |  55 ++++++++++++++++++
>   hw/arm/virt-acpi-build.c | 119 +++++++++++++++++++++++++++++++++++----
>   hw/arm/virt.c            | 109 ++++++++++++++++++++++++++---------
>   hw/core/sysbus-fdt.c     |   3 +
>   include/hw/arm/smmuv3.h  |  16 ++++++
>   include/hw/arm/virt.h    |   2 +
>   6 files changed, 266 insertions(+), 38 deletions(-)
>