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

[Alex Williamson <alex.williamson@redhat.com>]

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