Re: [PATCH 01/14] KVM: arm64: Donate MMIO to the hypervisor

[Suzuki K Poulose]

On 10/03/2026 12:49, Sebastian Ene wrote:
> From: Mostafa Saleh <smostafa@xxxxxxxxxx>
>
> Add a function to donate MMIO to the hypervisor so IOMMU hypervisor
> drivers can use that to protect the MMIO of IOMMU.
> The initial attempt to implement this was to have a new flag to
> "___pkvm_host_donate_hyp" to accept MMIO. However that had many problems,
> it was quite intrusive for host/hyp to check/set page state to make it
> aware of MMIO and to encode the state in the page table in that case.
> Which is called in paths that can be sensitive to performance (FFA, VMs..)
>
> As donating MMIO is very rare, and we don’t need to encode the full
> state, it’s reasonable to have a separate function to do this.
> It will init the host s2 page table with an invalid leaf with the owner ID
> to prevent the host from mapping the page on faults.
>
> Also, prevent kvm_pgtable_stage2_unmap() from removing owner ID from
> stage-2 PTEs, as this can be triggered from recycle logic under memory
> pressure. There is no code relying on this, as all ownership changes is
> done via kvm_pgtable_stage2_set_owner()
>
> For error path in IOMMU drivers, add a function to donate MMIO back
> from hyp to host.
>
> Signed-off-by: Mostafa Saleh <smostafa@xxxxxxxxxx>

nit: Your Signed-off-by: is missing. Even if you haven't made any
changes, when you are sending something, you need your S-o-B.

Suzuki