Re: [PATCH v2 4/4] KVM: arm64: Release the ownership of the hyp rx buffer to Trustzone

[Sudeep Holla <sudeep.holla@arm.com>]

On Wed, Mar 05, 2025 at 07:34:26PM +0000, Will Deacon wrote:
> On Wed, Mar 05, 2025 at 09:41:04AM +0000, Sudeep Holla wrote:
> > On Wed, Mar 05, 2025 at 12:45:23AM +0000, Will Deacon wrote:
> > > Hmm, the FFA spec is characteristically unclear as to whether or not we
> > > need to release the rx buffer in the case that the flags indicate use of
> > > the rx buffer but the returned partition count is 0.
> > > 
> > > Sudeep -- do you know what we should be doing in that case?
> > > 
> > 
> > We need to call RX_RELEASE here. I went back to the spec to confirm the
> > same again.
> > 
> > v1.2 EAC0 spec Section 7.2.2.4.2 Transfer of buffer ownership
> > (Or just look for the section title in any version of the spec)
> > "
> > 2. Ownership transfer for the RX buffer takes place as follows.
> >     2. For a framework message,
> >        1. Completion of the FFA_PARTITION_INFO_GET ABI transfers the ownership
> >        of the caller’s RX buffer from the Producer to the Consumer.
> > 3. For both types of messages, an invocation of the following FF-A ABIs
> >     transfers the ownership from the Consumer to the Producer.
> >        1. FFA_MSG_WAIT ...
> >        2. FFA_RX_RELEASE.
> > "
> > 
> > Hope that helps, can dig deeper if there are any ambiguities around this.
> 
> Thanks Sudeep, but that also makes it sound like we need the RX_RELEASE
> even if we're not using the RX buffer per the input flags. :/
> 

Good spot, I had forgotten about the input flags that can avoid using the
buffer. I will see if we can improve the spec in that regards.

-- 
Regards,
Sudeep