Re: [PATCH 4/5] hw/arm/virt: Add support for smmuv3 device

[Daniel P . Berrangé]

On Tue, Apr 15, 2025 at 10:25:42AM +0100, Jonathan Cameron wrote:
> On Tue, 15 Apr 2025 09:11:03 +0100
> Shameer Kolothum <shameerali.kolothum.thodi@huawei.com> wrote:
> 
> > Allow cold-plug of smmuv3 device to virt If the machine wide smmuv3
> > or a virtio-iommu is not specified.
> > 
> > Also restrict the usage if virt <= 9.2. This will prevent accidently
> > creating a SMMUv3 device on machines prior to 9.2 and cause failure
> > on migrating to machines with same version but has a legacy smmuv3
> > device.
> 
> Hi,
> 
> As we discussed internally I'm not convinced we need to prevent this 
> particular
> way for a user to shoot themselves in the foot.
> 
> To be a problem they have to specifically request an old machine + the
> device that didn't exist for that machine, then migrate to a real old
> version of QEMU.  Agreed it is possible but I'm not sure we need to
> prevent that particular crazy.

Agreed, there are a million ways to screw up using old machine types
with new features, so there's no compelling need to single out smmu for
special protection in this respect.

With regards,
Daniel
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