Hi Bertrand,
On Wed, Feb 11, 2026 at 6:16 PM Bertrand Marquis
<bertrand.marquis@arm.com> wrote:
>
> rxtx_unmap() checks RX ownership without holding the RX/TX locks and
> only enforces the ownership rule when FFA_RX_ACQUIRE is supported. This
> allows a vCPU to acquire RX between the check and unmap, and it lets
> RXTX_UNMAP proceed while RX is owned when buffers are not forwarded to
> firmware.
>
> Hold rx_lock/tx_lock across the ownership check and unmap, and deny
> RXTX_UNMAP whenever RX is owned, independent of RX_ACQUIRE support. For
> teardown, release RX ownership under the same lock window; use
> FFA_RX_RELEASE directly because rx_lock is held, and clear the local
> flag when the firmware path is unavailable.
>
> Functional impact: RXTX_UNMAP now reliably returns DENIED while RX is
> owned, and teardown releases/clears ownership without a race.
>
> Signed-off-by: Bertrand Marquis <bertrand.marquis@arm.com>
> ---
> Changes since v1:
> - Remove marking rx buffer as free during teardown as it is useless
> - Add a comment when calling rxtx_unmap during teardown to remind code
> readers that true is for teardown mode
> ---
> xen/arch/arm/tee/ffa_rxtx.c | 32 +++++++++++++++++++++++++++++---
> 1 file changed, 29 insertions(+), 3 deletions(-)
Looks good:
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>
Cheers,
Jens
>
> diff --git a/xen/arch/arm/tee/ffa_rxtx.c b/xen/arch/arm/tee/ffa_rxtx.c
> index eff95a7955d7..c4fc4c4934af 100644
> --- a/xen/arch/arm/tee/ffa_rxtx.c
> +++ b/xen/arch/arm/tee/ffa_rxtx.c
> @@ -220,7 +220,7 @@ err_unlock_rxtx:
> return ret;
> }
>
> -static int32_t rxtx_unmap(struct domain *d)
> +static int32_t rxtx_unmap(struct domain *d, bool teardown)
> {
> struct ffa_ctx *ctx = d->arch.tee;
> int32_t ret = FFA_RET_OK;
> @@ -234,6 +234,32 @@ static int32_t rxtx_unmap(struct domain *d)
> goto err_unlock_rxtx;
> }
>
> + if ( !ctx->rx_is_free )
> + {
> + if ( teardown )
> + {
> + if ( ffa_fw_supports_fid(FFA_RX_ACQUIRE) )
> + {
> + int32_t rel_ret;
> +
> + /* Can't use ffa_rx_release() while holding rx_lock. */
> + rel_ret = ffa_simple_call(FFA_RX_RELEASE, ctx->ffa_id,
> + 0, 0, 0);
> + if ( rel_ret )
> + gdprintk(XENLOG_DEBUG,
> + "ffa: RX release during teardown failed: %d\n",
> + rel_ret);
> + }
> + }
> + else
> + {
> + gdprintk(XENLOG_DEBUG,
> + "ffa: RXTX_UNMAP denied, RX buffer owned by VM\n");
> + ret = FFA_RET_DENIED;
> + goto err_unlock_rxtx;
> + }
> + }
> +
> if ( ffa_fw_supports_fid(FFA_RX_ACQUIRE) )
> {
> ret = ffa_rxtx_unmap(ffa_get_vm_id(d));
> @@ -261,7 +287,7 @@ err_unlock_rxtx:
>
> int32_t ffa_handle_rxtx_unmap(void)
> {
> - return rxtx_unmap(current->domain);
> + return rxtx_unmap(current->domain, false);
> }
>
> int32_t ffa_rx_acquire(struct ffa_ctx *ctx, void **buf, size_t *buf_size)
> @@ -369,7 +395,7 @@ int32_t ffa_rxtx_domain_init(struct domain *d)
>
> void ffa_rxtx_domain_destroy(struct domain *d)
> {
> - rxtx_unmap(d);
> + rxtx_unmap(d, true /* teardown */);
> }
>
> void *ffa_rxtx_spmc_rx_acquire(void)
> --
> 2.52.0
>