Re: [PATCH v9 11/25] iommu/arm-smmu-v3-kvm: Add the kernel driver

[Mostafa Saleh <smostafa@google.com>]

On Mon, Nov 09, 2026 at 04:16:53PM -0800, Nicolin Chen wrote:
> On Mon, Nov 09, 2026 at 10:47:46AM +0000, Mostafa Saleh wrote:
> > On Thu, Nov 05, 2026 at 01:06:18PM -0800, Nicolin Chen wrote:
> > > On Thu, Oct 15, 2026 at 08:08:42PM +0000, Mostafa Saleh wrote:
> > > > diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > > > +#ifdef CONFIG_ARM_SMMU_V3_PKVM
> > > > +/*
> > > > + * Two devices are involved: the aux device bound to this driver, and the
> > > > + * physical platform device bound to the pKVM init driver, which only uses it
> > > > + * for discovery. This driver keeps using the platform device, as it carries
> > > > + * the fwnode the IOMMU core and consumers link to, the DMA configuration and
> > > > + * the IRQs.
> > > 
> > > It would be nicer to have a diagram or so to show the co-relationship
> > > among different devices and drivers.
> > > 
> > > I assume the regular arm-smmu-v3 driver is a part of the picture too,
> > > when the pkvm driver binding fails?
> > > 
> > 
> > I can add some ASCII diagram.
> > If pKVM driver fails, no aux devices are created and the main driver
> > probes the platform SMMUv3 devices as usual.
> 
> I didn't check closely, but would it be safe to do so?
> 
> Is pkvm aware of the missing SMMU device and handling it properly?
> 
> When pkvm is enabled and the SMMU device is supposed to be a pkvm
> device, should it not fall back to the main driver?

If pKVM fails to init for any reason (unsupported layout or non-coherent
HW) the SMMU will be bound to the main driver so the system remains
functional.

However, pKVM will not be safe in that case regarding DMA isolation
as the status quo.
In Android, in that case, pKVM clears the FW (called pvmfw) that loads
the protected VM and authenticate it so any protected VM knows the
system is not trusted. This part is not upstream yet. [1]

However, there is not much that pKVM can do and I think it is better to
keep the system functional in that case than causing a panic or failing
KVM init for example.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/virt/kvm/arm/pkvm.rst#n106
Thanks,
Mostafa

> 
> Nicolin