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

Will Deacon
2025-03-05T20:04:34Z

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. :/

Will