Re: [PATCH v2 3/4] KVM: arm64: Map the hypervisor FF-A buffers on ffa init

Will Deacon
2025-03-04T02:21:32Z

On Tue, Mar 04, 2025 at 12:53:25AM +0000, Sebastian Ene wrote:
> On Mon, Mar 03, 2025 at 11:43:03PM +0000, Will Deacon wrote:
> > On Thu, Feb 27, 2025 at 06:17:48PM +0000, Sebastian Ene wrote:
> > > Map the hypervisor's buffers irrespective to the host and return
> > > a linux error code from the FF-A error code on failure. Remove
> > > the unmap ff-a buffers calls from the hypervisor as it will
> > > never be called.
> > > Prevent the host from using FF-A directly with Trustzone
> > > if the hypervisor could not map its own buffers.
> > >
> > > Signed-off-by: Sebastian Ene <sebastianene@google.com>
> > > ---
> > > arch/arm64/kvm/hyp/nvhe/ffa.c | 46 +++++++++++++----------------------
> > > 1 file changed, 17 insertions(+), 29 deletions(-)
> >
> > [...]
> >
> > > @@ -861,6 +842,7 @@ int hyp_ffa_init(void *pages)
> > > {
> > > struct arm_smccc_res res;
> > > void *tx, *rx;
> > > + int ret;
> > >
> > > if (kvm_host_psci_config.smccc_version < ARM_SMCCC_VERSION_1_2)
> > > return 0;
> > > @@ -911,5 +893,11 @@ int hyp_ffa_init(void *pages)
> > > .lock = __HYP_SPIN_LOCK_UNLOCKED,
> > > };
> > >
> > > + /* Map our hypervisor buffers into the SPMD */
> > > + ret = ffa_map_hyp_buffers();
> > > + if (ret)
> > > + return ret;
> >
> > Doesn't calling RXTX_MAP here undo the fix from c9c012625e12 ("KVM:
> > arm64: Trap FFA_VERSION host call in pKVM") where we want to allow for
> > the host to negotiate the version lazily?
>
> We still have the same behaviour where we don't allow memory
> sharing to happen until the version is negotiated but this
> separates the hypervisor buffer mapping part from the host.

Sadly, the spec doesn't restrict this to the memory sharing calls:

| [...] negotiation of the version must happen before an invocation of
| any other FF-A ABI

We're also probing the minimum rxtx size in hyp_ffa_post_init() so doing
this here is doubly wrong.

So I think we should probably just drop this patch.

Will