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

[Will Deacon <will@kernel.org>]

On Thu, Feb 27, 2025 at 06:17:49PM +0000, Sebastian Ene wrote:
> Introduce the release FF-A call to notify Trustzone that the hypervisor
> has finished copying the data from the buffer shared with Trustzone to
> the non-secure partition.
> 
> Reported-by: Andrei Homescu <ahomescu@google.com>
> Signed-off-by: Sebastian Ene <sebastianene@google.com>
> ---
>  arch/arm64/kvm/hyp/nvhe/ffa.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
> index 861f24de97cb..7da0203f1ee9 100644
> --- a/arch/arm64/kvm/hyp/nvhe/ffa.c
> +++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
> @@ -725,6 +725,7 @@ static void do_ffa_part_get(struct arm_smccc_res *res,
>  	DECLARE_REG(u32, uuid3, ctxt, 4);
>  	DECLARE_REG(u32, flags, ctxt, 5);
>  	u32 count, partition_sz, copy_sz;
> +	struct arm_smccc_res _res;
>  
>  	hyp_spin_lock(&host_buffers.lock);
>  	if (!host_buffers.rx) {
> @@ -741,7 +742,7 @@ static void do_ffa_part_get(struct arm_smccc_res *res,
>  
>  	count = res->a2;
>  	if (!count)
> -		goto out_unlock;
> +		goto release_rx;
>  
>  	if (hyp_ffa_version > FFA_VERSION_1_0) {
>  		/* Get the number of partitions deployed in the system */
> @@ -757,10 +758,12 @@ static void do_ffa_part_get(struct arm_smccc_res *res,
>  	copy_sz = partition_sz * count;
>  	if (copy_sz > KVM_FFA_MBOX_NR_PAGES * PAGE_SIZE) {
>  		ffa_to_smccc_res(res, FFA_RET_ABORTED);
> -		goto out_unlock;
> +		goto release_rx;
>  	}
>  
>  	memcpy(host_buffers.rx, hyp_buffers.rx, copy_sz);
> +release_rx:
> +	ffa_rx_release(&_res);

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?

Will