Re: [PATCH v26 13/17] vfio: create mapped iova list when vIOMMU is enabled

[Kirti Wankhede]

On 9/26/2020 3:53 AM, Alex Williamson wrote:
> On Wed, 23 Sep 2020 04:54:15 +0530
> Kirti Wankhede <kwankhede@nvidia.com> wrote:
>
> > Create mapped iova list when vIOMMU is enabled. For each mapped iova
> > save translated address. Add node to list on MAP and remove node from
> > list on UNMAP.
> > This list is used to track dirty pages during migration.
> >
> > Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
> > ---
> >   hw/vfio/common.c              | 58 ++++++++++++++++++++++++++++++++++++++-----
> >   include/hw/vfio/vfio-common.h |  8 ++++++
> >   2 files changed, 60 insertions(+), 6 deletions(-)
> >
> > diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> > index d4959c036dd1..dc56cded2d95 100644
> > --- a/hw/vfio/common.c
> > +++ b/hw/vfio/common.c
> > @@ -407,8 +407,8 @@ static bool 
> > vfio_listener_skipped_section(MemoryRegionSection *section)
> >   }
> >   
> >   /* Called with rcu_read_lock held.  */
> > -static bool vfio_get_vaddr(IOMMUTLBEntry *iotlb, void **vaddr,
> > -                           bool *read_only)
> > +static bool vfio_get_xlat_addr(IOMMUTLBEntry *iotlb, void **vaddr,
> > +                               ram_addr_t *ram_addr, bool *read_only)
> >   {
> >       MemoryRegion *mr;
> >       hwaddr xlat;
> > @@ -439,8 +439,17 @@ static bool vfio_get_vaddr(IOMMUTLBEntry *iotlb, void 
> > **vaddr,
> >           return false;
> >       }
> >   
> > -    *vaddr = memory_region_get_ram_ptr(mr) + xlat;
> > -    *read_only = !writable || mr->readonly;
> > +    if (vaddr) {
> > +        *vaddr = memory_region_get_ram_ptr(mr) + xlat;
> > +    }
> > +
> > +    if (ram_addr) {
> > +        *ram_addr = memory_region_get_ram_addr(mr) + xlat;
> > +    }
> > +
> > +    if (read_only) {
> > +        *read_only = !writable || mr->readonly;
> > +    }
> >   
> >       return true;
> >   }
> > @@ -450,7 +459,6 @@ static void vfio_iommu_map_notify(IOMMUNotifier *n, 
> > IOMMUTLBEntry *iotlb)
> >       VFIOGuestIOMMU *giommu = container_of(n, VFIOGuestIOMMU, n);
> >       VFIOContainer *container = giommu->container;
> >       hwaddr iova = iotlb->iova + giommu->iommu_offset;
> > -    bool read_only;
> >       void *vaddr;
> >       int ret;
> >   
> > @@ -466,7 +474,10 @@ static void vfio_iommu_map_notify(IOMMUNotifier *n, IOMMUTLBEntry *iotlb)
> >       rcu_read_lock();
> >   
> >       if ((iotlb->perm & IOMMU_RW) != IOMMU_NONE) {
> > -        if (!vfio_get_vaddr(iotlb, &vaddr, &read_only)) {
> > +        ram_addr_t ram_addr;
> > +        bool read_only;
> > +
> > +        if (!vfio_get_xlat_addr(iotlb, &vaddr, &ram_addr, &read_only)) {
> >               goto out;
> >           }
> >           /*
> > @@ -484,8 +495,28 @@ static void vfio_iommu_map_notify(IOMMUNotifier *n, 
> > IOMMUTLBEntry *iotlb)
> >                            "0x%"HWADDR_PRIx", %p) = %d (%m)",
> >                            container, iova,
> >                            iotlb->addr_mask + 1, vaddr, ret);
> > +        } else {
> > +            VFIOIovaRange *iova_range;
> > +
> > +            iova_range = g_malloc0(sizeof(*iova_range));
> > +            iova_range->iova = iova;
> > +            iova_range->size = iotlb->addr_mask + 1;
> > +            iova_range->ram_addr = ram_addr;
> > +
> > +            QLIST_INSERT_HEAD(&giommu->iova_list, iova_range, next);
> >           }
> >       } else {
> > +        VFIOIovaRange *iova_range, *tmp;
> > +
> > +        QLIST_FOREACH_SAFE(iova_range, &giommu->iova_list, next, tmp) {
> > +            if (iova_range->iova >= iova &&
> > +                iova_range->iova + iova_range->size <= iova +
> > +                                                       iotlb->addr_mask + 1) {
> > +                QLIST_REMOVE(iova_range, next);
> > +                g_free(iova_range);
> > +            }
> > +        }
> > +
>
>
> This is some pretty serious overhead... can't we trigger a replay when
> migration is enabled to build this information then? 

Are you suggesting to call memory_region_iommu_replay() before 
vfio_sync_dirty_bitmap(), which would call vfio_iommu_map_notify() where 
iova list of mapping is maintained? Then in the notifer check if 
migration_is_running() and container->dirty_pages_supported == true, 
then only create iova mapping tree? In this case how would we know that 
this is triggered by
vfio_sync_dirty_bitmap()
 -> memory_region_iommu_replay()
and we don't have to call vfio_dma_map()?

> We're looking at
> potentially thousands of entries, so a list is probably also not a good
> choice. 

Changing it to tree.

Thanks,
Kirti

 I don't think it's acceptable to incur this even when not
> migrating (ie. the vast majority of the time).  Thanks,
>
> Alex
>
> >           ret = vfio_dma_unmap(container, iova, iotlb->addr_mask + 1);
> >           if (ret) {
> >               error_report("vfio_dma_unmap(%p, 0x%"HWADDR_PRIx", "
> > @@ -642,6 +673,7 @@ static void vfio_listener_region_add(MemoryListener 
> > *listener,
> >               g_free(giommu);
> >               goto fail;
> >           }
> > +        QLIST_INIT(&giommu->iova_list);
> >           QLIST_INSERT_HEAD(&container->giommu_list, giommu, giommu_next);
> >           memory_region_iommu_replay(giommu->iommu, &giommu->n);
> >   
> > @@ -740,6 +772,13 @@ static void vfio_listener_region_del(MemoryListener *listener,
> >           QLIST_FOREACH(giommu, &container->giommu_list, giommu_next) {
> >               if (MEMORY_REGION(giommu->iommu) == section->mr &&
> >                   giommu->n.start == section->offset_within_region) {
> > +                VFIOIovaRange *iova_range, *tmp;
> > +
> > +                QLIST_FOREACH_SAFE(iova_range, &giommu->iova_list, next, tmp) {
> > +                    QLIST_REMOVE(iova_range, next);
> > +                    g_free(iova_range);
> > +                }
> > +
> >                   memory_region_unregister_iommu_notifier(section->mr,
> >                                                           &giommu->n);
> >                   QLIST_REMOVE(giommu, giommu_next);
> > @@ -1541,6 +1580,13 @@ static void vfio_disconnect_container(VFIOGroup *group)
> >           QLIST_REMOVE(container, next);
> >   
> >           QLIST_FOREACH_SAFE(giommu, &container->giommu_list, giommu_next, tmp) {
> > +            VFIOIovaRange *iova_range, *itmp;
> > +
> > +            QLIST_FOREACH_SAFE(iova_range, &giommu->iova_list, next, itmp) {
> > +                QLIST_REMOVE(iova_range, next);
> > +                g_free(iova_range);
> > +            }
> > +
> >               memory_region_unregister_iommu_notifier(
> >                       MEMORY_REGION(giommu->iommu), &giommu->n);
> >               QLIST_REMOVE(giommu, giommu_next);
> > diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
> > index 0a1651eda2d0..aa7524fe2cc5 100644
> > --- a/include/hw/vfio/vfio-common.h
> > +++ b/include/hw/vfio/vfio-common.h
> > @@ -89,11 +89,19 @@ typedef struct VFIOContainer {
> >       QLIST_ENTRY(VFIOContainer) next;
> >   } VFIOContainer;
> >   
> > +typedef struct VFIOIovaRange {
> > +    hwaddr iova;
> > +    size_t size;
> > +    ram_addr_t ram_addr;
> > +    QLIST_ENTRY(VFIOIovaRange) next;
> > +} VFIOIovaRange;
> > +
> >   typedef struct VFIOGuestIOMMU {
> >       VFIOContainer *container;
> >       IOMMUMemoryRegion *iommu;
> >       hwaddr iommu_offset;
> >       IOMMUNotifier n;
> > +    QLIST_HEAD(, VFIOIovaRange) iova_list;
> >       QLIST_ENTRY(VFIOGuestIOMMU) giommu_next;
> >   } VFIOGuestIOMMU;
> >