Re: [PATCH v8 11/25] iommu/arm-smmu-v3-kvm: Add the kernel driver

[Jason Gunthorpe <jgg@ziepe.ca>]

On Wed, Sep 23, 2026 at 11:52:36AM +0000, Mostafa Saleh wrote:
> I can add more info in the cover letter about the code split. Mainly:
> - arm-smmu-v3-kvm.c: Is the kernel driver for KVM SMMUv3 (this runs in
>   EL1 and can use all the kernel functions).
>   The main job of this driver is for discovery, it doesn't do anything
>   else in the runtime.

Maybe call this el1 stub or something like that?

guest_pkvm_stub.c
pkvm/hyp.c

?

> > > +extern struct pkvm_iommu_ops kvm_nvhe_sym(smmu_ops);
> > > +
> > > +static size_t				kvm_arm_smmu_count;
> > > +static struct hyp_arm_smmu_v3_device	*kvm_arm_smmu_array;
> > > +static size_t				kvm_arm_smmu_cur;
> > 
> > That spaces/tabs in those two lines look a bit odd..
> > 
> 
> These are tabs to indent the variables, similar cases exist in the
> SMMUv3 driver, check arm_smmu_cmdq and friends for example.

Personally I hate this style, it is a huge PITA for maintenance and
makes diffs bigger than they need to do. I remove it whenever I have
the chance :)

> TBH, this is a bit of a hack. The hypervisor can not allocate memory
> at the runtime. All of the hypervisor memory comes from a carveout
> allocated at boot (see kvm_hyp_reserve())
> 
> So we allocate the worst case for memory mapping with leaf granule. But
> the hypervisor also need to allocate L2 pointers and the SID space can
> be massive making the upper limit for this too large.
> 
> However, smmu_hyp_pgt_pages() defines the minimum pages required,
> actual allocation comes from the command line, so it is possible to
> tune the system without re-compiling the kernel.
> 
> Thinking about it now, we can just drop the 500 as this is the lower
> bound, earlier versions of this series would allocate the carveout
> based on this size, but it is not needed anymore.

I see, and you can't scan the ACPI to figure out all the SIDs used at
this point to get an exact estimation?

Not being able to manage memory after boot is rather an extreme
limitation.. But a huge amount of RMM's API complexity comes from its
granular memory management so I can't really fault that..

Jason