Re: [dpdk-dev] [PATCH 2/6] vfio: don't fail to DMA map if memory is already mapped

["Gaëtan Rivet" <gaetan.rivet@6wind.com>]

On Wed, Feb 13, 2019 at 11:10:22AM +0200, Shahaf Shuler wrote:
> Currently vfio DMA map function will fail in case the same memory
> segment is mapped twice.
> 
> This is too strict, as this is not an error to map the same memory
> twice.
> 
> Instead, use the kernel return value to detect such state and have the
> DMA function to return as successful.
> 
> For type1 mapping the kernel driver first implementation returns EBUSY
> and since kernel 3.11 returns EEXISTS. For spapr mapping EBUSY is returned
> since kernel 4.10.
> 

What is the earliest version supported by DPDK? I thought 3.10 was
dropped, should we care about the 3.11 return value?

> Signed-off-by: Shahaf Shuler <shahafs@mellanox.com>
> ---
>  lib/librte_eal/linuxapp/eal/eal_vfio.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/librte_eal/linuxapp/eal/eal_vfio.c b/lib/librte_eal/linuxapp/eal/eal_vfio.c
> index 48ca9465d4..2a2d655b37 100644
> --- a/lib/librte_eal/linuxapp/eal/eal_vfio.c
> +++ b/lib/librte_eal/linuxapp/eal/eal_vfio.c
> @@ -1263,7 +1263,11 @@ vfio_type1_dma_mem_map(int vfio_container_fd, uint64_t vaddr, uint64_t iova,
>  				VFIO_DMA_MAP_FLAG_WRITE;
>  
>  		ret = ioctl(vfio_container_fd, VFIO_IOMMU_MAP_DMA, &dma_map);
> -		if (ret) {
> +		/**
> +		 * In case the mapping was already done EEXIST will be
> +		 * returned from kernel.
> +		 */
> +		if ((ret != -EEXIST) && (ret != -EBUSY)) {

Won't a ret == 0 trigger the error then?

It seems ifdef about linux versions are not common in vfio code, but
bar that I think it would be cleaner to restrict the acceptable
error to it.

When a version will be dropped it will be much easier to remove the
related code instead of digging in the commit logs, and leaving both
would not be clean.

>  			RTE_LOG(ERR, EAL, "  cannot set up DMA remapping, error %i (%s)\n",
>  				errno, strerror(errno));
>  				return -1;
> @@ -1324,7 +1328,11 @@ vfio_spapr_dma_do_map(int vfio_container_fd, uint64_t vaddr, uint64_t iova,
>  				VFIO_DMA_MAP_FLAG_WRITE;
>  
>  		ret = ioctl(vfio_container_fd, VFIO_IOMMU_MAP_DMA, &dma_map);
> -		if (ret) {
> +		/**
> +		 * In case the mapping was already done EBUSY will be
> +		 * returned from kernel.
> +		 */
> +		if (ret != -EBUSY) {
>  			RTE_LOG(ERR, EAL, "  cannot set up DMA remapping, error %i (%s)\n",
>  				errno, strerror(errno));
>  				return -1;
> -- 
> 2.12.0
> 

-- 
Gaëtan Rivet
6WIND