[PATCH] eal: fix DMA mask validation inconsistency in IOVA VA

[PATCH] eal: fix DMA mask validation inconsistency in IOVA VA

[Shani Peretz]

When --iova-mode is explicitly specified in command line, DMA mask
constraints were not being validated, leading to potential runtime
failures when device DMA capabilities are exceeded.

The issue occurred because rte_bus_get_iommu_class() was only called
during IOVA mode auto-detection, but this function has the important
side effect of triggering DMA mask detection (e.g., Intel IOMMU
address width checking via pci_device_iommu_support_va()).

This created an inconsistency, when choosing explicit mode,
the DMA checks are bypassed, but when choosing auto-detection mode,
the constraints are checked and enforced.

The fix moves rte_bus_get_iommu_class() outside the conditional logic
to ensure it's always called during EAL initialization.

Fixes: 4374ebc24bc1 ("malloc: modify error message for DMA mask check")
Cc: stable@dpdk.org

Signed-off-by: Shani Peretz <shperetz@nvidia.com>
---
 lib/eal/freebsd/eal.c | 6 +++++-
 lib/eal/linux/eal.c   | 5 ++++-
 lib/eal/windows/eal.c | 5 ++++-
 3 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/lib/eal/freebsd/eal.c b/lib/eal/freebsd/eal.c
index c1ab8d86d2..0f957919d3 100644
--- a/lib/eal/freebsd/eal.c
+++ b/lib/eal/freebsd/eal.c
@@ -670,12 +670,16 @@ rte_eal_init(int argc, char **argv)
 	 * with a message describing the cause.
 	 */
 	has_phys_addr = internal_conf->no_hugetlbfs == 0;
+
+	/* Always call rte_bus_get_iommu_class() to trigger DMA mask detection and validation */
+	enum rte_iova_mode bus_iova_mode = rte_bus_get_iommu_class();
+
 	iova_mode = internal_conf->iova_mode;
 	if (iova_mode == RTE_IOVA_DC) {
 		EAL_LOG(DEBUG, "Specific IOVA mode is not requested, autodetecting");
 		if (has_phys_addr) {
 			EAL_LOG(DEBUG, "Selecting IOVA mode according to bus requests");
-			iova_mode = rte_bus_get_iommu_class();
+			iova_mode = bus_iova_mode;
 			if (iova_mode == RTE_IOVA_DC) {
 				if (!RTE_IOVA_IN_MBUF) {
 					iova_mode = RTE_IOVA_VA;
diff --git a/lib/eal/linux/eal.c b/lib/eal/linux/eal.c
index 52efb8626b..3a0c9c9db6 100644
--- a/lib/eal/linux/eal.c
+++ b/lib/eal/linux/eal.c
@@ -1042,10 +1042,13 @@ rte_eal_init(int argc, char **argv)
 
 	phys_addrs = rte_eal_using_phys_addrs() != 0;
 
+	/* Always call rte_bus_get_iommu_class() to trigger DMA mask detection and validation */
+	enum rte_iova_mode bus_iova_mode = rte_bus_get_iommu_class();
+
 	/* if no EAL option "--iova-mode=<pa|va>", use bus IOVA scheme */
 	if (internal_conf->iova_mode == RTE_IOVA_DC) {
 		/* autodetect the IOVA mapping mode */
-		enum rte_iova_mode iova_mode = rte_bus_get_iommu_class();
+		enum rte_iova_mode iova_mode = bus_iova_mode;
 
 		if (iova_mode == RTE_IOVA_DC) {
 			EAL_LOG(DEBUG, "Buses did not request a specific IOVA mode.");
diff --git a/lib/eal/windows/eal.c b/lib/eal/windows/eal.c
index 4f0a164d9b..2502ec3c3d 100644
--- a/lib/eal/windows/eal.c
+++ b/lib/eal/windows/eal.c
@@ -348,12 +348,15 @@ rte_eal_init(int argc, char **argv)
 		has_phys_addr = false;
 	}
 
+	/* Always call rte_bus_get_iommu_class() to trigger DMA mask detection and validation */
+	enum rte_iova_mode bus_iova_mode = rte_bus_get_iommu_class();
+
 	iova_mode = internal_conf->iova_mode;
 	if (iova_mode == RTE_IOVA_DC) {
 		EAL_LOG(DEBUG, "Specific IOVA mode is not requested, autodetecting");
 		if (has_phys_addr) {
 			EAL_LOG(DEBUG, "Selecting IOVA mode according to bus requests");
-			iova_mode = rte_bus_get_iommu_class();
+			iova_mode = bus_iova_mode;
 			if (iova_mode == RTE_IOVA_DC) {
 				if (!RTE_IOVA_IN_MBUF) {
 					iova_mode = RTE_IOVA_VA;
-- 
2.34.1

Re: [PATCH] eal: fix DMA mask validation inconsistency in IOVA VA

[Burakov, Anatoly]

On 9/8/2025 6:34 PM, Shani Peretz wrote:
> When --iova-mode is explicitly specified in command line, DMA mask
> constraints were not being validated, leading to potential runtime
> failures when device DMA capabilities are exceeded.
> 
> The issue occurred because rte_bus_get_iommu_class() was only called
> during IOVA mode auto-detection, but this function has the important
> side effect of triggering DMA mask detection (e.g., Intel IOMMU
> address width checking via pci_device_iommu_support_va()).
> 
> This created an inconsistency, when choosing explicit mode,
> the DMA checks are bypassed, but when choosing auto-detection mode,
> the constraints are checked and enforced.
> 
> The fix moves rte_bus_get_iommu_class() outside the conditional logic
> to ensure it's always called during EAL initialization.
> 
> Fixes: 4374ebc24bc1 ("malloc: modify error message for DMA mask check")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Shani Peretz <shperetz@nvidia.com>
> ---

Acked-by: Anatoly Burakov <anatoly.burakov@intel.com>

-- 
Thanks,
Anatoly