Re: [PATCH 0/2] firmware: arm_ffa: Fix RXTX_MAP buffer size regressions

[Sudeep Holla]

On Mon, Jun 01, 2026 at 03:45:10PM -0500, Seth Forshee wrote:
> Commit 83210251fd70 ("firmware: arm_ffa: Use the correct buffer size
> during RXTX_MAP") caused a regression for some FF-A implementations. It
> has the effect of passing the size of the page-aligned buffers to
> FFA_RXTX_MAP, which may be larger than the maximum size supported by the
> SPMC. When this happens FFA_RXTX_MAP will fail with INVALID_PARAMETERS.
> 
> The following patches deal with two distinct scenarios which lead to
> this issue. With FF-A v1.2+, FFA_FEATURES can specify a maximum supported
> RX/TX buffer size, so patch 1 decodes this field and honors the maximum if
> specified. For FF-A v1.1 and earlier the maximum is unknown, so patch 2
> deals with this by first attempting FFA_RXTX_MAP with the page-aligned
> buffer size (preserving the behavior introduced by commit 83210251fd70).
> If this fails due to invalid parameters it retries with the minimum buffer
> size from FFA_FEATURES.
> 
> Testing was done with FF-A v1.1 and v1.2 implementations, both of which
> reject buffer sizes larger than 4K. Both implementations were tested with
> 4K, 16K, and 64K pages. Without these patches, probe fails for page sizes
> larger than 4K with the message "failed to register FFA RxTx buffers."
> With the patches probe succeeds for all page sizes.
> 
> The patches are based on for-next/ffa/fixes.

for-next/ffa/updates has patches queued for v7.2.

> 
> Signed-off-by: Seth Forshee <sforshee@xxxxxxxxxx>
> ---
> Seth Forshee (2):
>       firmware: arm_ffa: Honor maximum RX/TX buffer size
>       firmware: arm_ffa: Fall back to minimum buffer size if RXTX_MAP fails
> 
>  drivers/firmware/arm_ffa/driver.c | 51 ++++++++++++++++++++++++++++++++++-----
>  1 file changed, 45 insertions(+), 6 deletions(-)

Wondering if these 2 fixes can be merged into one and simplified something
like(untested) patch below(rebased on linux-next or for-next/ffa/updates)

Regards,
Sudeep

-->8
diff --git a/drivers/firmware/arm_ffa/driver.c b/drivers/firmware/arm_ffa/driver.c
index 0f468362c288..5ffe21c568b7 100644
--- a/drivers/firmware/arm_ffa/driver.c
+++ b/drivers/firmware/arm_ffa/driver.c
@@ -32,6 +32,7 @@
 #include <linux/interrupt.h>
 #include <linux/io.h>
 #include <linux/kernel.h>
+#include <linux/minmax.h>
 #include <linux/module.h>
 #include <linux/mm.h>
 #include <linux/mutex.h>
@@ -59,7 +60,9 @@
        (FIELD_PREP(SENDER_ID_MASK, (s)) | FIELD_PREP(RECEIVER_ID_MASK, (r)))

 #define RXTX_MAP_MIN_BUFSZ_MASK        GENMASK(1, 0)
-#define RXTX_MAP_MIN_BUFSZ(x)  ((x) & RXTX_MAP_MIN_BUFSZ_MASK)
+#define RXTX_MAP_MAX_BUFSZ_MASK        GENMASK(31, 16)
+#define RXTX_MAP_MIN_BUFSZ(x)  (FIELD_GET(RXTX_MAP_MIN_BUFSZ_MASK, (x)))
+#define RXTX_MAP_MAX_BUFSZ(x)  (FIELD_GET(RXTX_MAP_MAX_BUFSZ_MASK, (x)))

 #define FFA_MAX_NOTIFICATIONS          64

@@ -2101,7 +2104,7 @@ static int ffa_probe(struct platform_device *pdev)
 {
        int ret;
        u32 buf_sz;
-       size_t rxtx_bufsz = SZ_4K;
+       size_t rxtx_min_bufsz = SZ_4K, rxtx_bufsz, rxtx_max_bufsz = 0;

        if (IS_BUILTIN(CONFIG_ARM_FFA_TRANSPORT) &&
            is_protected_kvm_enabled() && !is_pkvm_initialized())
@@ -2132,15 +2135,18 @@ static int ffa_probe(struct platform_device *pdev)
        ret = ffa_features(FFA_FN_NATIVE(RXTX_MAP), 0, &buf_sz, NULL);
        if (!ret) {
                if (RXTX_MAP_MIN_BUFSZ(buf_sz) == 1)
-                       rxtx_bufsz = SZ_64K;
+                       rxtx_min_bufsz = SZ_64K;
                else if (RXTX_MAP_MIN_BUFSZ(buf_sz) == 2)
-                       rxtx_bufsz = SZ_16K;
+                       rxtx_min_bufsz = SZ_16K;
                else
-                       rxtx_bufsz = SZ_4K;
+                       rxtx_min_bufsz = SZ_4K;
+
+               rxtx_max_bufsz = RXTX_MAP_MAX_BUFSZ(buf_sz) * SZ_4K;
+               if (rxtx_max_bufsz != 0 && rxtx_max_bufsz < rxtx_min_bufsz)
+                       rxtx_max_bufsz = rxtx_min_bufsz;
        }

-       rxtx_bufsz = PAGE_ALIGN(rxtx_bufsz);
-       drv_info->rxtx_bufsz = rxtx_bufsz;
+       rxtx_bufsz = min_not_zero(PAGE_ALIGN(rxtx_min_bufsz), rxtx_max_bufsz);
        drv_info->rx_buffer = alloc_pages_exact(rxtx_bufsz, GFP_KERNEL);
        if (!drv_info->rx_buffer) {
                ret = -ENOMEM;
@@ -2156,10 +2162,17 @@ static int ffa_probe(struct platform_device *pdev)
        ret = ffa_rxtx_map(virt_to_phys(drv_info->tx_buffer),
                           virt_to_phys(drv_info->rx_buffer),
                           rxtx_bufsz / FFA_PAGE_SIZE);
+       if (ret == -EINVAL && !rxtx_max_bufsz && rxtx_min_bufsz < rxtx_bufsz) {
+               rxtx_bufsz = rxtx_min_bufsz;
+               ret = ffa_rxtx_map(virt_to_phys(drv_info->tx_buffer),
+                                  virt_to_phys(drv_info->rx_buffer),
+                                  rxtx_bufsz / FFA_PAGE_SIZE);
+       }
        if (ret) {
                pr_err("failed to register FFA RxTx buffers\n");
                goto free_pages;
        }
+       drv_info->rxtx_bufsz = rxtx_bufsz;

        mutex_init(&drv_info->rx_lock);
        mutex_init(&drv_info->tx_lock);