Re: [RFC PATCH 0/5] hw/arm/virt: Add support for user-creatable nested SMMUv3

[Daniel P . Berrangé]

On Fri, Nov 08, 2024 at 12:52:37PM +0000, Shameer Kolothum via wrote:
> Hi,
> 
> This series adds initial support for a user-creatable "arm-smmuv3-nested"
> device to Qemu. At present the Qemu ARM SMMUv3 emulation is per machine
> and cannot support multiple SMMUv3s.
> 
> In order to support vfio-pci dev assignment with vSMMUv3, the physical
> SMMUv3 has to be configured in nested mode. Having a pluggable
> "arm-smmuv3-nested" device enables us to have multiple vSMMUv3 for Guests
> running on a host with multiple physical SMMUv3s. A few benefits of doing
> this are,

I'm not very familiar with arm, but from this description I'm not
really seeing how "nesting" is involved here. You're only talking
about the host and 1 L1 guest, no L2 guest.

Also what is the relation between the physical SMMUv3 and the guest
SMMUv3 that's referenced ? Is this in fact some form of host device
passthrough rather than nesting ?

With regards,
Daniel
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