Re: [PATCH V3 10/42] vfio/container: restore DMA vaddr

["Cédric Le Goater" <clg@redhat.com>]

On 5/12/25 17:32, Steve Sistare wrote:
> 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.
> 
> The listener calls a special dma_map handler that passes the new VA of each
> section to the kernel using VFIO_DMA_MAP_FLAG_VADDR.  Restore the normal
> handler at the end.
> 
> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
> ---
>   hw/vfio/container.c  | 15 +++++++++++++--
>   hw/vfio/cpr-legacy.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
>   2 files changed, 61 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/vfio/container.c b/hw/vfio/container.c
> index a554683..0e02726 100644
> --- a/hw/vfio/container.c
> +++ b/hw/vfio/container.c
> @@ -137,6 +137,8 @@ static int vfio_legacy_dma_unmap_one(const VFIOContainerBase *bcontainer,
>       int ret;
>       Error *local_err = NULL;
>   
> +    assert(!container->cpr.reused);

assert -> g_assert

this can be called at runtime, which would mean crashing QEMU in case
of error. Doing an error_report() call is more friendly.


Thanks,

C.


> +
>       if (iotlb && vfio_container_dirty_tracking_is_started(bcontainer)) {
>           if (!vfio_container_devices_dirty_tracking_is_supported(bcontainer) &&
>               bcontainer->dirty_pages_supported) {
> @@ -691,8 +693,17 @@ static bool vfio_container_connect(VFIOGroup *group, AddressSpace *as,
>       }
>       group_was_added = true;
>   
> -    if (!vfio_listener_register(bcontainer, errp)) {
> -        goto fail;
> +    /*
> +     * 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
> +     * dma_map to supply the new vaddr, and the calls will match the mappings
> +     * remembered by the kernel.
> +     */
> +    if (!cpr_reused) {
> +        if (!vfio_listener_register(bcontainer, errp)) {
> +            goto fail;
> +        }
>       }
>   
>       bcontainer->initialized = true;
> diff --git a/hw/vfio/cpr-legacy.c b/hw/vfio/cpr-legacy.c
> index 519d772..bbcf71e 100644
> --- a/hw/vfio/cpr-legacy.c
> +++ b/hw/vfio/cpr-legacy.c
> @@ -11,11 +11,13 @@
>   #include "hw/vfio/vfio-container.h"
>   #include "hw/vfio/vfio-cpr.h"
>   #include "hw/vfio/vfio-device.h"
> +#include "hw/vfio/vfio-listener.h"
>   #include "migration/blocker.h"
>   #include "migration/cpr.h"
>   #include "migration/migration.h"
>   #include "migration/vmstate.h"
>   #include "qapi/error.h"
> +#include "qemu/error-report.h"
>   
>   static bool vfio_dma_unmap_vaddr_all(VFIOContainer *container, Error **errp)
>   {
> @@ -32,6 +34,34 @@ static bool vfio_dma_unmap_vaddr_all(VFIOContainer *container, Error **errp)
>       return true;
>   }
>   
> +/*
> + * Set the new @vaddr for any mappings registered during cpr load.
> + * Reused is cleared thereafter.
> + */
> +static int vfio_legacy_cpr_dma_map(const VFIOContainerBase *bcontainer,
> +                                   hwaddr iova, ram_addr_t size, void *vaddr,
> +                                   bool readonly)
> +{
> +    const VFIOContainer *container = container_of(bcontainer, VFIOContainer,
> +                                                  bcontainer);
> +    struct vfio_iommu_type1_dma_map map = {
> +        .argsz = sizeof(map),
> +        .flags = VFIO_DMA_MAP_FLAG_VADDR,
> +        .vaddr = (__u64)(uintptr_t)vaddr,
> +        .iova = iova,
> +        .size = size,
> +    };
> +
> +    assert(container->cpr.reused);
> +> +    if (ioctl(container->fd, VFIO_IOMMU_MAP_DMA, &map)) {
> +        error_report("vfio_legacy_cpr_dma_map (iova %lu, size %ld, va %p): %s",
> +                     iova, size, vaddr, strerror(errno));
> +        return -errno;
> +    }
> +
> +    return 0;
> +}
>   
>   static bool vfio_cpr_supported(VFIOContainer *container, Error **errp)
>   {
> @@ -63,12 +93,24 @@ static int vfio_container_pre_save(void *opaque)
>   static int vfio_container_post_load(void *opaque, int version_id)
>   {
>       VFIOContainer *container = opaque;
> +    VFIOContainerBase *bcontainer = &container->bcontainer;
>       VFIOGroup *group;
>       VFIODevice *vbasedev;
> +    Error *err = NULL;
> +
> +    if (!vfio_listener_register(bcontainer, &err)) {
> +        error_report_err(err);
> +        return -1;
> +    }
>   
>       container->cpr.reused = false;
>   
>       QLIST_FOREACH(group, &container->group_list, container_next) {
> +        VFIOIOMMUClass *vioc = VFIO_IOMMU_GET_CLASS(bcontainer);
> +
> +        /* Restore original dma_map function */
> +        vioc->dma_map = vfio_legacy_dma_map;
> +
>           QLIST_FOREACH(vbasedev, &group->device_list, next) {
>               vbasedev->cpr.reused = false;
>           }
> @@ -80,6 +122,7 @@ 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,
> @@ -104,6 +147,11 @@ bool vfio_legacy_cpr_register_container(VFIOContainer *container, Error **errp)
>   
>       vmstate_register(NULL, -1, &vfio_container_vmstate, container);
>   
> +    /* During incoming CPR, divert calls to dma_map. */
> +    if (container->cpr.reused) {
> +        VFIOIOMMUClass *vioc = VFIO_IOMMU_GET_CLASS(bcontainer);
> +        vioc->dma_map = vfio_legacy_cpr_dma_map;
> +    }
>       return true;
>   }
>