Re: [PATCH V1 06/26] vfio/container: preserve DMA mappings

["Cédric Le Goater" <clg@redhat.com>]

On 1/29/25 15:43, Steve Sistare wrote:
> Preserve DMA mappings during cpr-transfer.
> 
> In the container pre_save handler, suspend the use of virtual addresses
> in DMA mappings with VFIO_DMA_UNMAP_FLAG_VADDR, because guest RAM will
> be remapped at a different VA after exec.  DMA to already-mapped pages
> continues.
> 
> Because the vaddr is temporarily invalid, mediated devices cannot be
> supported, so add a blocker for them.  This restriction will not apply
> to iommufd containers when CPR is added for them in a future patch.
> 
> In new QEMU, do not register the memory listener at device creation time.
> Register it later, in the container post_load handler, after all vmstate
> that may affect regions and mapping boundaries has been loaded.  The
> post_load registration will cause the listener to invoke its callback on
> each flat section, and the calls will match the mappings remembered by the
> kernel.  Modify vfio_dma_map (which is called by the listener) to pass the
> new VA to the kernel using VFIO_DMA_MAP_FLAG_VADDR.
> 
> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
> ---
>   hw/vfio/container.c           | 44 +++++++++++++++++++++++++++++++++++++++----
>   hw/vfio/cpr-legacy.c          | 32 +++++++++++++++++++++++++++++++
>   include/hw/vfio/vfio-common.h |  3 +++
>   3 files changed, 75 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/vfio/container.c b/hw/vfio/container.c
> index 81d0ccc..2b5125e 100644
> --- a/hw/vfio/container.c
> +++ b/hw/vfio/container.c
> @@ -32,6 +32,7 @@
>   #include "trace.h"
>   #include "qapi/error.h"
>   #include "migration/cpr.h"
> +#include "migration/blocker.h"
>   #include "pci.h"
>   
>   VFIOGroupList vfio_group_list =
> @@ -132,6 +133,8 @@ static int vfio_legacy_dma_unmap(const VFIOContainerBase *bcontainer,
>       int ret;
>       Error *local_err = NULL;
>   
> +    assert(!container->reused);
> +
>       if (iotlb && vfio_devices_all_dirty_tracking_started(bcontainer)) {
>           if (!vfio_devices_all_device_dirty_tracking(bcontainer) &&
>               bcontainer->dirty_pages_supported) {
> @@ -183,12 +186,24 @@ static int vfio_legacy_dma_map(const VFIOContainerBase *bcontainer, hwaddr iova,
>                                                     bcontainer);
>       struct vfio_iommu_type1_dma_map map = {
>           .argsz = sizeof(map),
> -        .flags = VFIO_DMA_MAP_FLAG_READ,
>           .vaddr = (__u64)(uintptr_t)vaddr,
>           .iova = iova,
>           .size = size,
>       };
>   
> +    /*
> +     * Set the new vaddr for any mappings registered during cpr load.
> +     * Reused is cleared thereafter.
> +     */
> +    if (container->reused) {
> +        map.flags = VFIO_DMA_MAP_FLAG_VADDR;
> +        if (ioctl(container->fd, VFIO_IOMMU_MAP_DMA, &map)) {
> +            goto fail;
> +        }
> +        return 0;
> +    }

This is a bit ugly.

When reaching routine vfio_attach_device(), could we detect that CPR is
in progress and replace the 'VFIOIOMMUClass *' temporarily with a set of
CPR specific handlers ?


> +
> +    map.flags = VFIO_DMA_MAP_FLAG_READ;
>       if (!readonly) {
>           map.flags |= VFIO_DMA_MAP_FLAG_WRITE;
>       }
> @@ -205,7 +220,11 @@ static int vfio_legacy_dma_map(const VFIOContainerBase *bcontainer, hwaddr iova,
>           return 0;
>       }
>   
> -    error_report("VFIO_MAP_DMA failed: %s", strerror(errno));
> +fail:
> +    error_report("vfio_dma_map %s (iova %lu, size %ld, va %p): %s",
> +        (container->reused ? "VADDR" : ""), iova, size, vaddr,
> +        strerror(errno));
> +


FYI, I am currently trying to remove this error report.


>       return -errno;
>   }
>   
> @@ -689,8 +708,17 @@ static bool vfio_connect_container(VFIOGroup *group, AddressSpace *as,
>       group->container = container;
>       QLIST_INSERT_HEAD(&container->group_list, group, container_next);
>   
> -    bcontainer->listener = vfio_memory_listener;
> -    memory_listener_register(&bcontainer->listener, bcontainer->space->as);
> +    /*
> +     * If reused, register the listener later, after all state that may
> +     * affect regions and mapping boundaries has been cpr load'ed.  Later,
> +     * the listener will invoke its callback on each flat section and call
> +     * vfio_dma_map to supply the new vaddr, and the calls will match the
> +     * mappings remembered by the kernel.
> +     */
> +    if (!reused) {
> +        bcontainer->listener = vfio_memory_listener;
> +        memory_listener_register(&bcontainer->listener, bcontainer->space->as);
> +    }

oh ! This is an important change. Please move in its own patch.

>       if (bcontainer->error) {
>           error_propagate_prepend(errp, bcontainer->error,
> @@ -1002,6 +1030,13 @@ static bool vfio_legacy_attach_device(const char *name, VFIODevice *vbasedev,
>           return false;
>       }
>   
> +    if (vbasedev->mdev) {
> +        error_setg(&vbasedev->cpr_mdev_blocker,
> +                   "CPR does not support vfio mdev %s", vbasedev->name);
> +        migrate_add_blocker_modes(&vbasedev->cpr_mdev_blocker, &error_fatal,
> +                                  MIG_MODE_CPR_TRANSFER, -1);
> +    }

same here, the cpr blocker for mdev devices should be in its own patch.


>       bcontainer = &group->container->bcontainer;
>       vbasedev->bcontainer = bcontainer;
>       QLIST_INSERT_HEAD(&bcontainer->device_list, vbasedev, container_next);
> @@ -1018,6 +1053,7 @@ static void vfio_legacy_detach_device(VFIODevice *vbasedev)
>       QLIST_REMOVE(vbasedev, container_next);
>       vbasedev->bcontainer = NULL;
>       trace_vfio_detach_device(vbasedev->name, group->groupid);
> +    migrate_del_blocker(&vbasedev->cpr_mdev_blocker);
>       vfio_put_base_device(vbasedev);
>       vfio_put_group(group);
>   }
> diff --git a/hw/vfio/cpr-legacy.c b/hw/vfio/cpr-legacy.c
> index ce6f14e..f3a31d1 100644
> --- a/hw/vfio/cpr-legacy.c
> +++ b/hw/vfio/cpr-legacy.c
> @@ -14,6 +14,21 @@
>   #include "migration/vmstate.h"
>   #include "qapi/error.h"
>   
> +static bool vfio_dma_unmap_vaddr_all(VFIOContainer *container, Error **errp)
> +{
> +    struct vfio_iommu_type1_dma_unmap unmap = {
> +        .argsz = sizeof(unmap),
> +        .flags = VFIO_DMA_UNMAP_FLAG_VADDR | VFIO_DMA_UNMAP_FLAG_ALL,
> +        .iova = 0,
> +        .size = 0,
> +    };
> +    if (ioctl(container->fd, VFIO_IOMMU_UNMAP_DMA, &unmap)) {
> +        error_setg_errno(errp, errno, "vfio_dma_unmap_vaddr_all");
> +        return false;
> +    }
> +    return true;
> +}
> +
>   static bool vfio_cpr_supported(VFIOContainer *container, Error **errp)
>   {
>       if (!ioctl(container->fd, VFIO_CHECK_EXTENSION, VFIO_UPDATE_VADDR)) {
> @@ -29,12 +44,27 @@ static bool vfio_cpr_supported(VFIOContainer *container, Error **errp)
>       }
>   }
>   
> +static int vfio_container_pre_save(void *opaque)
> +{
> +    VFIOContainer *container = opaque;
> +    Error *err = NULL;
> +
> +    if (!vfio_dma_unmap_vaddr_all(container, &err)) {
> +        error_report_err(err);

We should modify vmstate_save_state_v() to call .pre_save() handlers
with an Error ** parameter.


Thanks,

C.



> +        return -1;
> +    }
> +    return 0;
> +}
> +
>   static int vfio_container_post_load(void *opaque, int version_id)
>   {
>       VFIOContainer *container = opaque;
> +    VFIOContainerBase *bcontainer = &container->bcontainer;
>       VFIOGroup *group;
>       VFIODevice *vbasedev;
>   
> +    bcontainer->listener = vfio_memory_listener;
> +    memory_listener_register(&bcontainer->listener, bcontainer->space->as);
>       container->reused = false;
>   
>       QLIST_FOREACH(group, &container->group_list, container_next) {
> @@ -49,6 +79,8 @@ static const VMStateDescription vfio_container_vmstate = {
>       .name = "vfio-container",
>       .version_id = 0,
>       .minimum_version_id = 0,
> +    .priority = MIG_PRI_LOW,  /* Must happen after devices and groups */
> +    .pre_save = vfio_container_pre_save,
>       .post_load = vfio_container_post_load,
>       .needed = cpr_needed_for_reuse,
>       .fields = (VMStateField[]) {
> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
> index a435a90..1e974e0 100644
> --- a/include/hw/vfio/vfio-common.h
> +++ b/include/hw/vfio/vfio-common.h
> @@ -143,6 +143,7 @@ typedef struct VFIODevice {
>       unsigned int flags;
>       VFIOMigration *migration;
>       Error *migration_blocker;
> +    Error *cpr_mdev_blocker;
>       OnOffAuto pre_copy_dirty_page_tracking;
>       OnOffAuto device_dirty_page_tracking;
>       bool dirty_pages_supported;
> @@ -310,6 +311,8 @@ int vfio_devices_query_dirty_bitmap(const VFIOContainerBase *bcontainer,
>   int vfio_get_dirty_bitmap(const VFIOContainerBase *bcontainer, uint64_t iova,
>                             uint64_t size, ram_addr_t ram_addr, Error **errp);
>   
> +void vfio_listener_register(VFIOContainerBase *bcontainer);
> +
>   /* Returns 0 on success, or a negative errno. */
>   bool vfio_device_get_name(VFIODevice *vbasedev, Error **errp);
>   void vfio_device_set_fd(VFIODevice *vbasedev, const char *str, Error **errp);