Re: [PATCH v2 10/20] vfio/common: Record DMA mapped IOVA ranges

[Alex Williamson]

On Wed, 22 Feb 2023 19:49:05 +0200
Avihai Horon <avihaih@nvidia.com> wrote:

> From: Joao Martins <joao.m.martins@oracle.com>
> 
> According to the device DMA logging uAPI, IOVA ranges to be logged by
> the device must be provided all at once upon DMA logging start.
> 
> As preparation for the following patches which will add device dirty
> page tracking, keep a record of all DMA mapped IOVA ranges so later they
> can be used for DMA logging start.
> 
> Note that when vIOMMU is enabled DMA mapped IOVA ranges are not tracked.
> This is due to the dynamic nature of vIOMMU DMA mapping/unmapping.
> Following patches will address the vIOMMU case specifically.
> 
> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
> Signed-off-by: Avihai Horon <avihaih@nvidia.com>
> ---
>  include/hw/vfio/vfio-common.h |  3 ++
>  hw/vfio/common.c              | 86 +++++++++++++++++++++++++++++++++--
>  2 files changed, 86 insertions(+), 3 deletions(-)
> 
> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
> index ee55d442b4..6f36876ce0 100644
> --- a/include/hw/vfio/vfio-common.h
> +++ b/include/hw/vfio/vfio-common.h
> @@ -23,6 +23,7 @@
>  
>  #include "exec/memory.h"
>  #include "qemu/queue.h"
> +#include "qemu/iova-tree.h"
>  #include "qemu/notify.h"
>  #include "ui/console.h"
>  #include "hw/display/ramfb.h"
> @@ -92,6 +93,8 @@ typedef struct VFIOContainer {
>      uint64_t max_dirty_bitmap_size;
>      unsigned long pgsizes;
>      unsigned int dma_max_mappings;
> +    IOVATree *mappings;
> +    QemuMutex mappings_mutex;
>      QLIST_HEAD(, VFIOGuestIOMMU) giommu_list;
>      QLIST_HEAD(, VFIOHostDMAWindow) hostwin_list;
>      QLIST_HEAD(, VFIOGroup) group_list;
> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> index 84f08bdbbb..6041da6c7e 100644
> --- a/hw/vfio/common.c
> +++ b/hw/vfio/common.c
> @@ -44,6 +44,7 @@
>  #include "migration/blocker.h"
>  #include "migration/qemu-file.h"
>  #include "sysemu/tpm.h"
> +#include "qemu/iova-tree.h"
>  
>  VFIOGroupList vfio_group_list =
>      QLIST_HEAD_INITIALIZER(vfio_group_list);
> @@ -426,6 +427,11 @@ void vfio_unblock_multiple_devices_migration(void)
>      multiple_devices_migration_blocker = NULL;
>  }
>  
> +static bool vfio_have_giommu(VFIOContainer *container)
> +{
> +    return !QLIST_EMPTY(&container->giommu_list);
> +}
> +
>  static void vfio_set_migration_error(int err)
>  {
>      MigrationState *ms = migrate_get_current();
> @@ -499,6 +505,51 @@ static bool 
> vfio_devices_all_running_and_mig_active(VFIOContainer *container)
>      return true;
>  }
>  
> +static int vfio_record_mapping(VFIOContainer *container, hwaddr iova,
> +                               hwaddr size, bool readonly)
> +{
> +    DMAMap map = {
> +        .iova = iova,
> +        .size = size - 1, /* IOVATree is inclusive, so subtract 1 from size 
> */
> +        .perm = readonly ? IOMMU_RO : IOMMU_RW,
> +    };
> +    int ret;
> +
> +    if (vfio_have_giommu(container)) {
> +        return 0;
> +    }
> +
> +    WITH_QEMU_LOCK_GUARD(&container->mappings_mutex) {
> +        ret = iova_tree_insert(container->mappings, &map);
> +        if (ret) {
> +            if (ret == IOVA_ERR_INVALID) {
> +                ret = -EINVAL;
> +            } else if (ret == IOVA_ERR_OVERLAP) {
> +                ret = -EEXIST;
> +            }
> +        }
> +    }
> +
> +    return ret;
> +}
> +
> +static void vfio_erase_mapping(VFIOContainer *container, hwaddr iova,
> +                                hwaddr size)
> +{
> +    DMAMap map = {
> +        .iova = iova,
> +        .size = size - 1, /* IOVATree is inclusive, so subtract 1 from size 
> */
> +    };
> +
> +    if (vfio_have_giommu(container)) {
> +        return;
> +    }
> +
> +    WITH_QEMU_LOCK_GUARD(&container->mappings_mutex) {
> +        iova_tree_remove(container->mappings, map);
> +    }
> +}

Nit, 'insert' and 'remove' to match the IOVATree semantics?

>  static int vfio_dma_unmap_bitmap(VFIOContainer *container,
>                                   hwaddr iova, ram_addr_t size,
>                                   IOMMUTLBEntry *iotlb)
> @@ -599,6 +650,8 @@ static int vfio_dma_unmap(VFIOContainer *container,
>                                              DIRTY_CLIENTS_NOCODE);
>      }
>  
> +    vfio_erase_mapping(container, iova, size);
> +
>      return 0;
>  }
>  
> @@ -612,6 +665,16 @@ static int vfio_dma_map(VFIOContainer *container, hwaddr 
> iova,
>          .iova = iova,
>          .size = size,
>      };
> +    int ret;
> +
> +    ret = vfio_record_mapping(container, iova, size, readonly);
> +    if (ret) {
> +        error_report("vfio: Failed to record mapping, iova: 0x%" HWADDR_PRIx
> +                     ", size: 0x" RAM_ADDR_FMT ", ret: %d (%s)",
> +                     iova, size, ret, strerror(-ret));
> +
> +        return ret;
> +    }

Is there no way to replay the mappings when a migration is started?
This seems like a horrible latency and bloat trade-off for the
possibility that the VM might migrate and the device might support
these features.  Our performance with vIOMMU is already terrible, I
can't help but believe this makes it worse.  Thanks,

Alex