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

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Message-ID: <20250305193425.GA32246@willie-the-truck>
Date: Wed, 5 Mar 2025 19:34:26 +0000
From: Will Deacon <will@...nel.org>
To: Sudeep Holla <sudeep.holla@....com>
Cc: Sebastian Ene <sebastianene@...gle.com>, catalin.marinas@....com,
	joey.gouly@....com, maz@...nel.org, oliver.upton@...ux.dev,
	snehalreddy@...gle.com, suzuki.poulose@....com,
	vdonnefort@...gle.com, yuzenghui@...wei.com, kvmarm@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	kernel-team@...roid.com, Andrei Homescu <ahomescu@...gle.com>
Subject: Re: [PATCH v2 4/4] KVM: arm64: Release the ownership of the hyp rx
 buffer to Trustzone

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