Re: [dpdk-dev] [PATCH dpdk 5/5] RFC: vfio/ppc64/spapr: Use correct bus addresses for DMA map

["Jonas Pfefferle1" <JPF@zurich.ibm.com>]

Alexey Kardashevskiy <aik@ozlabs.ru> wrote on 20/04/2017 16:22:01:

> From: Alexey Kardashevskiy <aik@ozlabs.ru>
> To: Jonas Pfefferle1 <JPF@zurich.ibm.com>
> Cc: dev@dpdk.org, Gowrishankar Muthukrishnan
> <gowrishankar.m@in.ibm.com>, Adrian Schuepbach <DRI@zurich.ibm.com>
> Date: 20/04/2017 16:22
> Subject: Re: [PATCH dpdk 5/5] RFC: vfio/ppc64/spapr: Use correct bus
> addresses for DMA map
>
> On 20/04/17 23:25, Alexey Kardashevskiy wrote:
> > On 20/04/17 19:04, Jonas Pfefferle1 wrote:
> >> Alexey Kardashevskiy <aik@ozlabs.ru> wrote on 20/04/2017 09:24:02:
> >>
> >>> From: Alexey Kardashevskiy <aik@ozlabs.ru>
> >>> To: dev@dpdk.org
> >>> Cc: Alexey Kardashevskiy <aik@ozlabs.ru>, JPF@zurich.ibm.com,
> >>> Gowrishankar Muthukrishnan <gowrishankar.m@in.ibm.com>
> >>> Date: 20/04/2017 09:24
> >>> Subject: [PATCH dpdk 5/5] RFC: vfio/ppc64/spapr: Use correct bus
> >>> addresses for DMA map
> >>>
> >>> VFIO_IOMMU_SPAPR_TCE_CREATE ioctl() returns the actual bus address
for
> >>> just created DMA window. It happens to start from zero because the
default
> >>> window is removed (leaving no windows) and new window starts from
zero.
> >>> However this is not guaranteed and the new window may start from
another
> >>> address, this adds an error check.
> >>>
> >>> Another issue is that IOVA passed to VFIO_IOMMU_MAP_DMA should be a
PCI
> >>> bus address while in this case a physical address of a user page is
used.
> >>> This changes IOVA to start from zero in a hope that the rest of DPDK
> >>> expects this.
> >>
> >> This is not the case. DPDK expects a 1:1 mapping PA==IOVA. It will use
the
> >> phys_addr of the memory segment it got from /proc/self/pagemap cf.
> >> librte_eal/linuxapp/eal/eal_memory.c. We could try setting it here to
the
> >> actual iova which basically makes the whole virtual to phyiscal
mapping
> >> with pagemap unnecessary which I believe should be the case for VFIO
> >> anyway. Pagemap should only be needed when using pci_uio.
> >
> >
> > Ah, ok, makes sense now. But it sure needs a big fat comment there as
it is
> > not obvious why host RAM address is used there as DMA window start is
not
> > guaranteed.
>
> Well, either way there is some bug - ms[i].phys_addr and ms[i].addr_64
both
> have exact same value, in my setup it is 3fffb33c0000 which is a
userspace
> address - at least ms[i].phys_addr must be physical address.

This might be the case if you are not using hugetlbfs i.e. passing
"--no-huge" cf. eal_memory.c:980

	/* hugetlbfs can be disabled */
	if (internal_config.no_hugetlbfs) {
		addr = mmap(NULL, internal_config.memory, PROT_READ |
PROT_WRITE,
				MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);
		if (addr == MAP_FAILED) {
			RTE_LOG(ERR, EAL, "%s: mmap() failed: %s\n", __func__,
					strerror(errno));
			return -1;
		}
		mcfg->memseg[0].phys_addr = (phys_addr_t)(uintptr_t)addr;
		mcfg->memseg[0].addr = addr;
		mcfg->memseg[0].hugepage_sz = RTE_PGSIZE_4K;
		mcfg->memseg[0].len = internal_config.memory;
		mcfg->memseg[0].socket_id = 0;
		return 0;
	}

If it fails to get the virt2phys mapping it actually assigns iovas starting
from 0 to the memory segments, cf. set_physaddrs eal_memory.c:263

>
>
> >
> >
> >>
> >>>
> >>> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> >>> ---
> >>>  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 46f951f4d..8b8e75c4f 100644
> >>> --- a/lib/librte_eal/linuxapp/eal/eal_vfio.c
> >>> +++ b/lib/librte_eal/linuxapp/eal/eal_vfio.c
> >>> @@ -658,7 +658,7 @@ vfio_spapr_dma_map(int vfio_container_fd)
> >>>  {
> >>>     const struct rte_memseg *ms = rte_eal_get_physmem_layout();
> >>>     int i, ret;
> >>> -
> >>> +   phys_addr_t io_offset;
> >>>     struct vfio_iommu_spapr_register_memory reg = {
> >>>        .argsz = sizeof(reg),
> >>>        .flags = 0
> >>> @@ -702,6 +702,13 @@ vfio_spapr_dma_map(int vfio_container_fd)
> >>>        return -1;
> >>>     }
> >>>
> >>> +   io_offset = create.start_addr;
> >>> +   if (io_offset) {
> >>> +      RTE_LOG(ERR, EAL, "  DMA offsets other than zero is not
> supported, "
> >>> +            "new window is created at %lx\n", io_offset);
> >>> +      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;
> >>> @@ -723,7 +730,7 @@ vfio_spapr_dma_map(int vfio_container_fd)
> >>>        dma_map.argsz = sizeof(struct vfio_iommu_type1_dma_map);
> >>>        dma_map.vaddr = ms[i].addr_64;
> >>>        dma_map.size = ms[i].len;
> >>> -      dma_map.iova = ms[i].phys_addr;
> >>> +      dma_map.iova = io_offset;
> >>>        dma_map.flags = VFIO_DMA_MAP_FLAG_READ |
> >>>               VFIO_DMA_MAP_FLAG_WRITE;
> >>>
> >>> @@ -735,6 +742,7 @@ vfio_spapr_dma_map(int vfio_container_fd)
> >>>           return -1;
> >>>        }
> >>>
> >>> +      io_offset += dma_map.size;
> >>>     }
> >>>
> >>>     return 0;
> >>> --
> >>> 2.11.0
> >>>
> >>
> >
> >
>
>
> --
> Alexey
>