Re: [PATCH v3 08/10] KVM: arm64: Handle FFA_MEM_LEND calls from the host

[Will Deacon <will@kernel.org>]

On Sun, Jul 13, 2025 at 11:59:57PM +0900, DaeRo Lee wrote:
> > > > Handle FFA_MEM_LEND calls from the host by treating them identically to
> > > > FFA_MEM_SHARE calls for the purposes of the host stage-2 page-table, but
> > > > forwarding on the original request to EL3.
> > > 
> > > I have a question about your patch.
> > > Does treating FFA_MEM_LEND as identical to FFA_MEM_SHARE imply that
> > > the host can still access the memory even after it has been lent?
> >
> > Only if your TZ implementation is broken and relies on the NS hypervisor
> > for isolation.
> 
> I believe pKVM is managing stage 2 isolation between Host and Non-secure Guest
> VMs or between Non-secure Guest VMs
> 
> <Quote DEN0140_FF-A_Memory Management Protocol>
> 2.2.1.2 Relayer responsibilities
> 10. Unmap the memory region from the translation regime of the Lender, if
> managed by the Relayer as specified in 1.2 Address translation regimes. This 
> must be done only if the memory region is in the Owner-EA state. This includes
> removing access to the memory region from any DMA capable devices assigned to 
> the Lender.
> 
> From the content, it seems that when performing a Lend operation, it's
> necessary to perform a Stage 2 unmap of the host memory area. Am I understanding
> this correctly?

No.

pKVM doesn't use FF-A to manage host/guest page ownership.

FF-A is only used for memory management with the Secure world, in which
case a LEND transaction will mean that the Secure world must prevent
Non-Secure access to the memory itself and not rely on pKVM to unmap
at stage-2.

Will