Re: [PATCH V1 07/26] vfio/container: recover from unmap-all-vaddr failure

[Steven Sistare <steven.sistare@oracle.com>]

On 2/4/2025 9:10 AM, Cédric Le Goater wrote:
> On 1/29/25 15:43, Steve Sistare wrote:
>> If there are multiple containers and unmap-all fails for some container, we
>> need to remap vaddr for the other containers for which unmap-all succeeded.
>> Recover by walking all address ranges of all containers to restore the vaddr
>> for each.  Do so by invoking the vfio listener callback, and passing a new
>> "remap" flag that tells it to restore a mapping without re-allocating new
>> userland data structures.
>>
>> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
>> ---
>>   hw/vfio/common.c              | 47 ++++++++++++++++++++++++++++++++++++++++++-
>>   hw/vfio/cpr-legacy.c          | 44 ++++++++++++++++++++++++++++++++++++++++
>>   include/hw/vfio/vfio-common.h |  6 +++++-
>>   3 files changed, 95 insertions(+), 2 deletions(-)
>>
>> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
>> index 7370332..c8ee71a 100644
>> --- a/hw/vfio/common.c
>> +++ b/hw/vfio/common.c
>> @@ -580,6 +580,13 @@ static void vfio_listener_region_add(MemoryListener *listener,
>>   {
>>       VFIOContainerBase *bcontainer = container_of(listener, VFIOContainerBase,
>>                                                    listener);
>> +    vfio_container_region_add(bcontainer, section, false);
>> +}
>> +
>> +void vfio_container_region_add(VFIOContainerBase *bcontainer,
>> +                               MemoryRegionSection *section,
>> +                               bool remap)
>> +{
> 
> vfio_container_region_add() is already complex enough. Please consider
> doing an initial refactoring before adding a new code path. It would be
> welcome !

I'll take a look after factoring out the cpr code into helpers as you
request below.

>>       hwaddr iova, end;
>>       Int128 llend, llsize;
>>       void *vaddr;
>> @@ -614,6 +621,30 @@ static void vfio_listener_region_add(MemoryListener *listener,
>>           int iommu_idx;
>>           trace_vfio_listener_region_add_iommu(section->mr->name, iova, end);
>> +
>> +        /*
>> +         * If remap, then VFIO_DMA_UNMAP_FLAG_VADDR has been called, and we
>> +         * want to remap the vaddr.  vfio_container_region_add was already
>> +         * called in the past, so the giommu already exists.  Find it and
>> +         * replay it, which calls vfio_dma_map further down the stack.
>> +         */
>> +
>> +        if (remap) {
>> +            hwaddr as_offset = section->offset_within_address_space;
>> +            hwaddr iommu_offset = as_offset - section->offset_within_region;
>> +
>> +            QLIST_FOREACH(giommu, &bcontainer->giommu_list, giommu_next) {
>> +                if (giommu->iommu_mr == iommu_mr &&
>> +                    giommu->iommu_offset == iommu_offset) {
>> +                    memory_region_iommu_replay(giommu->iommu_mr, &giommu->n);
>> +                    return;
>> +                }
>> +            }
>> +            error_report("Container cannot find iommu region %s offset %lx",
>> +                memory_region_name(section->mr), iommu_offset);
> 
> error_report() are not welcomed. We need to find a way to propagate
> this error.

I follow the existing practice in this function, which already reports other
errors.  This is called in the context of a memory listener region_add method,
so returning an error affects the signature of all listeners and should be a
seperate RFE.

>> +            goto fail;
>> +        }
> 
> Please introduce a vfio_cpr helper for the section above and move it
> under the hw/vfio/cpr* files.

OK.

>>           /*
>>            * FIXME: For VFIO iommu types which have KVM acceleration to
>>            * avoid bouncing all map/unmaps through qemu this way, this
>> @@ -656,7 +687,21 @@ static void vfio_listener_region_add(MemoryListener *listener,
>>        * about changes.
>>        */
>>       if (memory_region_has_ram_discard_manager(section->mr)) {
>> -        vfio_register_ram_discard_listener(bcontainer, section);
>> +        /*
>> +         * If remap, then VFIO_DMA_UNMAP_FLAG_VADDR has been called, and we
>> +         * want to remap the vaddr.  vfio_container_region_add was already
>> +         * called in the past, so the ram discard listener already exists.
>> +         * Call its populate function directly, which calls vfio_dma_map.
>> +         */
>> +        if (remap)  {
>> +            VFIORamDiscardListener *vrdl =
>> +                vfio_find_ram_discard_listener(bcontainer, section);
>> +            if (vrdl->listener.notify_populate(&vrdl->listener, section)) {
>> +                error_report("listener.notify_populate failed");
>> +            }
>> +        } else {
>> +            vfio_register_ram_discard_listener(bcontainer, section);
>> +        }
> 
> idem.

OK.

>>           return;
>>       }
>> diff --git a/hw/vfio/cpr-legacy.c b/hw/vfio/cpr-legacy.c
>> index f3a31d1..3139de1 100644
>> --- a/hw/vfio/cpr-legacy.c
>> +++ b/hw/vfio/cpr-legacy.c
>> @@ -26,9 +26,18 @@ static bool vfio_dma_unmap_vaddr_all(VFIOContainer *container, Error **errp)
>>           error_setg_errno(errp, errno, "vfio_dma_unmap_vaddr_all");
>>           return false;
>>       }
>> +    container->vaddr_unmapped = true;
>>       return true;>   }
>> +static void vfio_region_remap(MemoryListener *listener,
>> +                              MemoryRegionSection *section)
>> +{
>> +    VFIOContainer *container = container_of(listener, VFIOContainer,
>> +                                            remap_listener);
>> +    vfio_container_region_add(&container->bcontainer, section, true);
>> +}
>> +
>>   static bool vfio_cpr_supported(VFIOContainer *container, Error **errp)
>>   {
>>       if (!ioctl(container->fd, VFIO_CHECK_EXTENSION, VFIO_UPDATE_VADDR)) {
>> @@ -88,6 +97,37 @@ static const VMStateDescription vfio_container_vmstate = {
>>       }
>>   };
>> +static int vfio_cpr_fail_notifier(NotifierWithReturn *notifier,
>> +                                  MigrationEvent *e, Error **errp)
>> +{
>> +    VFIOContainer *container =
>> +        container_of(notifier, VFIOContainer, cpr_transfer_notifier);
>> +    VFIOContainerBase *bcontainer = &container->bcontainer;
>> +
>> +    if (e->type != MIG_EVENT_PRECOPY_FAILED) {
>> +        return 0;
>> +    }
>> +
>> +    if (container->vaddr_unmapped) {
>> +        /*
>> +         * Force a call to vfio_region_remap for each mapped section by
>> +         * temporarily registering a listener, which calls vfio_dma_map
>> +         * further down the stack. Set reused so vfio_dma_map restores vaddr.
>> +         */
>> +        container->reused = true;
>> +        container->remap_listener = (MemoryListener) {
>> +            .name = "vfio recover",
>> +            .region_add = vfio_region_remap
>> +        };
>> +        memory_listener_register(&container->remap_listener,
>> +                                 bcontainer->space->as);
>> +        memory_listener_unregister(&container->remap_listener);
>> +        container->reused = false;
>> +        container->vaddr_unmapped = false;
>> +    }> +    return 0;
>> +}
>> +
>>   bool vfio_legacy_cpr_register_container(VFIOContainer *container, Error **errp)
>>   {
>>       VFIOContainerBase *bcontainer = &container->bcontainer;
>> @@ -104,6 +144,9 @@ bool vfio_legacy_cpr_register_container(VFIOContainer *container, Error **errp)
>>       vmstate_register(NULL, -1, &vfio_container_vmstate, container);
>> +    migration_add_notifier_mode(&container->cpr_transfer_notifier,
>> +                                vfio_cpr_fail_notifier,
>> +                                MIG_MODE_CPR_TRANSFER);
>>       return true;>   }
>> @@ -114,4 +157,5 @@ void vfio_legacy_cpr_unregister_container(VFIOContainer *container)
>>       vfio_cpr_unregister_container(bcontainer);
>>       migrate_del_blocker(&container->cpr_blocker);
>>       vmstate_unregister(NULL, &vfio_container_vmstate, container);
>> +    migration_remove_notifier(&container->cpr_transfer_notifier);
>>   }
>> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
>> index 1e974e0..8a4a658 100644
>> --- a/include/hw/vfio/vfio-common.h
>> +++ b/include/hw/vfio/vfio-common.h
>> @@ -86,6 +86,9 @@ typedef struct VFIOContainer {
>>       unsigned iommu_type;
>>       Error *cpr_blocker;
>>       bool reused;
>> +    bool vaddr_unmapped;
>> +    NotifierWithReturn cpr_transfer_notifier;
>> +    MemoryListener remap_listener;
> 
> There are 5 attributes related to CPR, please add a CPR struct to hold
> them all.

OK.

- Steve

>>       QLIST_HEAD(, VFIOGroup) group_list;
>>   } VFIOContainer;
>> @@ -311,7 +314,8 @@ 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);
>> +void vfio_container_region_add(VFIOContainerBase *bcontainer,
>> +                               MemoryRegionSection *section, bool remap);
>>   /* Returns 0 on success, or a negative errno. */
>>   bool vfio_device_get_name(VFIODevice *vbasedev, Error **errp);
>