Re: [dpdk-dev] [PATCH] vfio: fix sPAPR IOMMU DMA window size

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 08/08/17 01:11, Jonas Pfefferle wrote:
> DMA window size needs to be big enough to span all memory segment's
> physical addresses. We do not need multiple levels of IOMMU tables
> as we already span ~70TB of physical memory with 16MB hugepages.
> 
> Signed-off-by: Jonas Pfefferle <jpf@zurich.ibm.com>
> ---
>  lib/librte_eal/linuxapp/eal/eal_vfio.c | 25 ++++++++++++++++++++++---
>  1 file changed, 22 insertions(+), 3 deletions(-)
> 
> diff --git a/lib/librte_eal/linuxapp/eal/eal_vfio.c b/lib/librte_eal/linuxapp/eal/eal_vfio.c
> index 946df7e..8502216 100644
> --- a/lib/librte_eal/linuxapp/eal/eal_vfio.c
> +++ b/lib/librte_eal/linuxapp/eal/eal_vfio.c
> @@ -722,6 +722,18 @@ vfio_type1_dma_map(int vfio_container_fd)
>  	return 0;
>  }
>  
> +static uint64_t
> +roundup_next_pow2(uint64_t n)
> +{
> +	uint32_t i;
> +
> +	n--;
> +	for (i = 1; i < sizeof(n) * CHAR_BIT; i += i)
> +		n |= n >> i;
> +
> +	return ++n;
> +}
> +

wow :)

QEMU does it using __builtin_ctzll() (used below for the page_shift)
without a loop:

https://git.qemu.org/gitweb.cgi?p=qemu.git;a=blob;f=include/qemu/host-utils.h;h=95cf4f4163e50457cdf808263065ca5ef3f935da;hb=f22ab6cb0c47bd2a2785b7d58130949bd7d8d9af#l382


Anyway, seems working.


Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>




>  static int
>  vfio_spapr_dma_map(int vfio_container_fd)
>  {
> @@ -759,10 +771,12 @@ vfio_spapr_dma_map(int vfio_container_fd)
>  		return -1;
>  	}
>  
> -	/* calculate window size based on number of hugepages configured */
> -	create.window_size = rte_eal_get_physmem_size();
> +	/* physicaly pages are sorted descending i.e. ms[0].phys_addr is max */
> +	/* create DMA window from 0 to max(phys_addr + len) */
> +	/* sPAPR requires window size to be a power of 2 */
> +	create.window_size = roundup_next_pow2(ms[0].phys_addr + ms[0].len);
>  	create.page_shift = __builtin_ctzll(ms->hugepage_sz);
> -	create.levels = 2;
> +	create.levels = 1;
>  
>  	ret = ioctl(vfio_container_fd, VFIO_IOMMU_SPAPR_TCE_CREATE, &create);
>  	if (ret) {
> @@ -771,6 +785,11 @@ vfio_spapr_dma_map(int vfio_container_fd)
>  		return -1;
>  	}
>  
> +	if (create.start_addr != 0) {
> +		RTE_LOG(ERR, EAL, "  DMA window start address != 0\n");
> +		return -1;
> +	}
> +
>  	/* map all DPDK segments for DMA. use 1:1 PA to IOVA mapping */
>  	for (i = 0; i < RTE_MAX_MEMSEG; i++) {
>  		struct vfio_iommu_type1_dma_map dma_map;
> 


-- 
Alexey