Re: Support SVM without PASID

[valmiki <valmikibow@gmail.com>]

On 8/7/2017 4:01 PM, Jean-Philippe Brucker wrote:
> On 05/08/17 06:14, valmiki wrote:
> [...]
>> Hi Jean, Thanks a lot, now i understood the flow. From vfio kernel
>> documentation we fill vaddr and iova in struct vfio_iommu_type1_dma_map
>> and pass them to VFIO. But if we use dynamic allocation in application
>> (say malloc), do we need to use dma API to get iova and then call
>> VFIO_IOMMU_MAP ioctl ?
>> If application needs multiple such dynamic allocations, then it need to
>> allocate large chunk and program it via VFIO_IOMMU_MAP ioctl and then
>> manage rest allocations requirements from this buffer ?
>
> Yes, without SVM, the application allocates large buffers, allocates IOVAs
> itself, and maps them with VFIO_IOMMU_MAP. Userspace doesn't rely on the
> DMA API at all, it manages IOVAs as it wants. Sizes passed to
> VFIO_IOMMU_MAP have to be multiples of the MMU or IOMMU page granularity
> (that is at least 4kB), and both iova and vaddr have to be aligned on that
> granularity as well. So malloc isn't really suitable in this case, you'll
> need mmap. The application can then implement a small allocator to manage
> the DMA pool created with VFIO_IOMMU_MAP.

Thanks Jean, I have a confusion allocate IOVA's in userspace means, how 
can user application decide IOVA address, can user application pick any 
random IOVA address ?

Regards,
Valmiki