Re: [Qemu-devel] [PATCH qemu v16 18/19] vfio/spapr: Create DMA window dynamically (SPAPR IOMMU v2)

[David Gibson <david@gibson.dropbear.id.au>]

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On Fri, May 27, 2016 at 01:49:19PM +1000, Alexey Kardashevskiy wrote:
> On 17/05/16 06:20, Alex Williamson wrote:
> > On Mon, 16 May 2016 14:52:41 +1000
> > Alexey Kardashevskiy <aik@ozlabs.ru> wrote:
> > 
> >> On 05/14/2016 08:26 AM, Alex Williamson wrote:
> >>> On Wed,  4 May 2016 16:52:30 +1000
> >>> Alexey Kardashevskiy <aik@ozlabs.ru> wrote:
> >>>  
> >>>> New VFIO_SPAPR_TCE_v2_IOMMU type supports dynamic DMA window management.
> >>>> This adds ability to VFIO common code to dynamically allocate/remove
> >>>> DMA windows in the host kernel when new VFIO container is added/removed.
> >>>>
> >>>> This adds VFIO_IOMMU_SPAPR_TCE_CREATE ioctl to vfio_listener_region_add
> >>>> and adds just created IOMMU into the host IOMMU list; the opposite
> >>>> action is taken in vfio_listener_region_del.
> >>>>
> >>>> When creating a new window, this uses heuristic to decide on the TCE table
> >>>> levels number.
> >>>>
> >>>> This should cause no guest visible change in behavior.
> >>>>
> >>>> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> >>>> ---
> >>>> Changes:
> >>>> v16:
> >>>> * used memory_region_iommu_get_page_sizes() in vfio_listener_region_add()
> >>>> * enforced no intersections between windows
> >>>>
> >>>> v14:
> >>>> * new to the series
> >>>> ---
> >>>>  hw/vfio/common.c | 133 ++++++++++++++++++++++++++++++++++++++++++++++++++-----
> >>>>  trace-events     |   2 +
> >>>>  2 files changed, 125 insertions(+), 10 deletions(-)
> >>>>
> >>>> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> >>>> index 03daf88..bd2dee8 100644
> >>>> --- a/hw/vfio/common.c
> >>>> +++ b/hw/vfio/common.c
> >>>> @@ -240,6 +240,18 @@ static int vfio_dma_map(VFIOContainer *container, hwaddr iova,
> >>>>      return -errno;
> >>>>  }
> >>>>
> >>>> +static bool range_contains(hwaddr start, hwaddr end, hwaddr addr)
> >>>> +{
> >>>> +    return start <= addr && addr <= end;
> >>>> +}  
> >>>
> >>> a) If you want a "range_foo" function then put it in range.h
> >>> b) I suspect there are already range.h functions that can do this.
> >>>  
> >>>> +
> >>>> +static bool vfio_host_win_intersects(VFIOHostDMAWindow *hostwin,
> >>>> +                                     hwaddr min_iova, hwaddr max_iova)
> >>>> +{
> >>>> +    return range_contains(hostwin->min_iova, hostwin->min_iova, min_iova) ||
> >>>> +        range_contains(min_iova, max_iova, hostwin->min_iova);
> >>>> +}  
> >>>
> >>> How is this different than ranges_overlap()?  
> >>>> +
> >>>>  static VFIOHostDMAWindow *vfio_host_win_lookup(VFIOContainer *container,
> >>>>                                                 hwaddr min_iova, hwaddr max_iova)
> >>>>  {
> >>>> @@ -279,6 +291,14 @@ static int vfio_host_win_add(VFIOContainer *container,
> >>>>      return 0;
> >>>>  }
> >>>>
> >>>> +static void vfio_host_win_del(VFIOContainer *container, hwaddr min_iova)
> >>>> +{
> >>>> +    VFIOHostDMAWindow *hostwin = vfio_host_win_lookup(container, min_iova, 1);
> >>>> +
> >>>> +    g_assert(hostwin);  
> >>>
> >>> Handle the error please.  
> >>
> >> Will this be enough?
> >>
> >>      if (!hostwin) {
> >>          error_report("%s: Cannot delete missing window at %"HWADDR_PRIx,
> >>                       __func__, min_iova);
> >>          return;
> >>      }
> > 
> > Better.  I was really thinking to return error to the caller, but if
> > the caller has no return path, perhaps this is as good as we can do.
> > Expect that I will push back on any assert() calls added to vfio.
> > 
> > 
> >>>> +    QLIST_REMOVE(hostwin, hostwin_next);
> >>>> +}
> >>>> +
> >>>>  static bool vfio_listener_skipped_section(MemoryRegionSection *section)
> >>>>  {
> >>>>      return (!memory_region_is_ram(section->mr) &&
> >>>> @@ -392,6 +412,69 @@ static void vfio_listener_region_add(MemoryListener *listener,
> >>>>      }
> >>>>      end = int128_get64(int128_sub(llend, int128_one()));
> >>>>
> >>>> +    if (container->iommu_type == VFIO_SPAPR_TCE_v2_IOMMU) {
> >>>> +        VFIOHostDMAWindow *hostwin;
> >>>> +        unsigned pagesizes = memory_region_iommu_get_page_sizes(section->mr);
> >>>> +        unsigned pagesize = (hwaddr)1 << ctz64(pagesizes);
> >>>> +        unsigned entries, pages;
> >>>> +        struct vfio_iommu_spapr_tce_create create = { .argsz = sizeof(create) };
> >>>> +
> >>>> +        trace_vfio_listener_region_add_iommu(iova, end);
> >>>> +        /*
> >>>> +         * FIXME: For VFIO iommu types which have KVM acceleration to
> >>>> +         * avoid bouncing all map/unmaps through qemu this way, this
> >>>> +         * would be the right place to wire that up (tell the KVM
> >>>> +         * device emulation the VFIO iommu handles to use).
> >>>> +         */
> >>>> +        create.window_size = int128_get64(section->size);
> >>>> +        create.page_shift = ctz64(pagesize);
> >>>> +        /*
> >>>> +         * SPAPR host supports multilevel TCE tables, there is some
> >>>> +         * heuristic to decide how many levels we want for our table:
> >>>> +         * 0..64 = 1; 65..4096 = 2; 4097..262144 = 3; 262145.. = 4
> >>>> +         */
> >>>> +        entries = create.window_size >> create.page_shift;
> >>>> +        pages = MAX((entries * sizeof(uint64_t)) / getpagesize(), 1);
> >>>> +        pages = MAX(pow2ceil(pages) - 1, 1); /* Round up */
> >>>> +        create.levels = ctz64(pages) / 6 + 1;
> >>>> +
> >>>> +        /* For now intersections are not allowed, we may relax this later */
> >>>> +        QLIST_FOREACH(hostwin, &container->hostwin_list, hostwin_next) {
> >>>> +            if (vfio_host_win_intersects(hostwin,
> >>>> +                    section->offset_within_address_space,
> >>>> +                    section->offset_within_address_space +
> >>>> +                    create.window_size - 1)) {
> >>>> +                goto fail;
> >>>> +            }
> >>>> +        }
> >>>> +
> >>>> +        ret = ioctl(container->fd, VFIO_IOMMU_SPAPR_TCE_CREATE, &create);
> >>>> +        if (ret) {
> >>>> +            error_report("Failed to create a window, ret = %d (%m)", ret);
> >>>> +            goto fail;
> >>>> +        }
> >>>> +
> >>>> +        if (create.start_addr != section->offset_within_address_space) {
> >>>> +            struct vfio_iommu_spapr_tce_remove remove = {
> >>>> +                .argsz = sizeof(remove),
> >>>> +                .start_addr = create.start_addr
> >>>> +            };
> >>>> +            error_report("Host doesn't support DMA window at %"HWADDR_PRIx", must be %"PRIx64,
> >>>> +                         section->offset_within_address_space,
> >>>> +                         create.start_addr);
> >>>> +            ioctl(container->fd, VFIO_IOMMU_SPAPR_TCE_REMOVE, &remove);
> >>>> +            ret = -EINVAL;
> >>>> +            goto fail;
> >>>> +        }
> >>>> +        trace_vfio_spapr_create_window(create.page_shift,
> >>>> +                                       create.window_size,
> >>>> +                                       create.start_addr);
> >>>> +
> >>>> +        vfio_host_win_add(container, create.start_addr,
> >>>> +                          create.start_addr + create.window_size - 1,
> >>>> +                          1ULL << create.page_shift);
> >>>> +    }  
> >>>
> >>> This is a function on its own, split it out and why not stop pretending
> >>> prereg is some sort of generic interface and let's just make a spapr
> >>> support file.  
> >>
> >>
> >> Yet another new file - spapr.c, or rename prereg.c to spapr.c and add this 
> >> stuff there?
> > 
> > prereg.c is already spapr specific, so I'd rename it and potentially
> > add this to it.
> 
> 
> It would help if you two decided what I should do about prereg.c vs.
> spapr.c - merge or keep 2 files. Thanks.

I'm not particularly fussed either way.  So I suggest putting the
prereg stuff in spapr.c for now, and we can move it out if/when
another platform starts using the mechanism.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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