RE: [PATCH v2] eal: fix DMA mask validation inconsistency in IOVA VA

[Shani Peretz <shperetz@nvidia.com>]

> -----Original Message-----
> From: Shani Peretz <shperetz@nvidia.com>
> Sent: Thursday, 18 September 2025 9:48
> To: dev@dpdk.org
> Cc: NBU-Contact-Thomas Monjalon (EXTERNAL) <thomas@monjalon.net>;
> Shani Peretz <shperetz@nvidia.com>; stable@dpdk.org; Bruce Richardson
> <bruce.richardson@intel.com>; Dmitry Kozlyuk <dmitry.kozliuk@gmail.com>;
> Tyler Retzlaff <roretzla@linux.microsoft.com>; Alejandro Lucero
> <alejandro.lucero@netronome.com>
> Subject: [PATCH v2] eal: fix DMA mask validation inconsistency in IOVA VA
> 
> 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


Rebased on latest main. Patch was already acked

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