Re: [dpdk-dev] [PATCH v2 3/5] bus/pci: use IOVAs check when setting IOVA mode

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

On 31-Aug-18 1:50 PM, Alejandro Lucero wrote:
> Although VT-d emulation currently only supports 39 bits, it could
> be iovas being within that supported range. This patch allows
> IOVA mode in such a case.
> 
> Indeed, memory initialization code can be modified for using lower
> virtual addresses than those used by the kernel for 64 bits processes
> by default, and therefore memsegs iovas can use 39 bits or less for
> most system. And this is likely 100% true for VMs.
> 
> Signed-off-by: Alejandro Lucero <alejandro.lucero@netronome.com>
> ---
>   drivers/bus/pci/linux/pci.c | 15 ++++++++++-----
>   1 file changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/bus/pci/linux/pci.c b/drivers/bus/pci/linux/pci.c
> index 04648ac..215dc10 100644
> --- a/drivers/bus/pci/linux/pci.c
> +++ b/drivers/bus/pci/linux/pci.c
> @@ -588,10 +588,11 @@
>   	fclose(fp);
>   
>   	mgaw = ((vtd_cap_reg & VTD_CAP_MGAW_MASK) >> VTD_CAP_MGAW_SHIFT) + 1;
> -	if (mgaw < X86_VA_WIDTH)
> -		return false;
>   
> -	return true;
> +	if (!rte_eal_check_dma_mask(mgaw))
> +		return true;
> +	else
> +		return false;

return rte_eal_check_dma_mask(mgaw) == 0; ?

>   }
>   #elif defined(RTE_ARCH_PPC_64)
>   static bool
> @@ -615,13 +616,17 @@
>   {
>   	struct rte_pci_device *dev = NULL;
>   	struct rte_pci_driver *drv = NULL;
> +	int iommu_dma_mask_check_done = 0;
>   
>   	FOREACH_DRIVER_ON_PCIBUS(drv) {
>   		FOREACH_DEVICE_ON_PCIBUS(dev) {
>   			if (!rte_pci_match(drv, dev))
>   				continue;
> -			if (!pci_one_device_iommu_support_va(dev))
> -				return false;
> +			if (!iommu_dma_mask_check_done) {
> +				if (!pci_one_device_iommu_support_va(dev))
> +					return false;
> +				iommu_dma_mask_check_done  = 1;
> +			}
>   		}

The commit message doesn't explain why are we only checking a single 
device. Indeed, i am not 100% clear as to why, so some explanation in 
the commit message and preferably a comment in code would be more than 
welcome :)

>   	}
>   	return true;
> 


-- 
Thanks,
Anatoly