RE: Support SVM without PASID

[Bharat Kumar Gogada <bharatku@xilinx.com>]

> Subject: RE: Support SVM without PASID
>=20
> > From: valmiki [mailto:valmikibow@gmail.com]
> > Sent: Saturday, August 12, 2017 8:11 PM
> >
> > 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 ?
> >
>=20
> yes, any address. In this mode the whole IOVA address space is owned by
> application, which just needs to use VFIO_IOMMU_MAP to setup
> IOVA->PA mapping in IOMMU (As Jean pointed out, input paramters
> are iova and vaddr. VFIO will figure out pa corresponding to vaddr).
>=20
Hi Kevin, I have a doubt in this case, what if someone assigns mmap returne=
d virtual address as iova address, then=20
EP will assume it is generating request on IOVA but in reality we are using=
 application allocated virtual address, then
it looks like we are working with application virtual address directly with=
out PASID. Is this valid ?

Regards,
Bharat