Re: [PATCH v2 06/12] vfio/pci: Introduce vfio_[attach/detach]_device

[Eric Auger <eric.auger@redhat.com>]

On 9/27/23 12:07, Duan, Zhenzhong wrote:
> Hi Eric,
>
>> -----Original Message-----
>> From: Eric Auger <eric.auger@redhat.com>
>> Sent: Wednesday, September 27, 2023 5:02 PM
>> Subject: Re: [PATCH v2 06/12] vfio/pci: Introduce vfio_[attach/detach]_device
>>
>> Hi Zhenzhong,
>>
>> On 9/26/23 13:32, Zhenzhong Duan wrote:
>>> From: Eric Auger <eric.auger@redhat.com>
>>>
>>> We want the VFIO devices to be able to use two different
>>> IOMMU backends, the legacy VFIO one and the new iommufd one.
>>>
>>> Introduce vfio_[attach/detach]_device which aim at hiding the
>>> underlying IOMMU backend (IOCTLs, datatypes, ...).
>>>
>>> Once vfio_attach_device completes, the device is attached
>>> to a security context and its fd can be used. Conversely
>>> When vfio_detach_device completes, the device has been
>>> detached from the security context.
>>>
>>> At the moment only the implementation based on the legacy
>>> container/group exists. Let's use it from the vfio-pci device.
>>> Subsequent patches will handle other devices.
>>>
>>> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>>> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
>>> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
>>> ---
>>>  include/hw/vfio/vfio-common.h |  3 ++
>>>  hw/vfio/common.c              | 68 +++++++++++++++++++++++++++++++++++
>>>  hw/vfio/pci.c                 | 50 +++-----------------------
>>>  hw/vfio/trace-events          |  2 +-
>>>  4 files changed, 77 insertions(+), 46 deletions(-)
>>>
>>> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
>>> index c4e7c3b4a7..12fbfbc37d 100644
>>> --- a/include/hw/vfio/vfio-common.h
>>> +++ b/include/hw/vfio/vfio-common.h
>>> @@ -225,6 +225,9 @@ void vfio_put_group(VFIOGroup *group);
>>>  struct vfio_device_info *vfio_get_device_info(int fd);
>>>  int vfio_get_device(VFIOGroup *group, const char *name,
>>>                      VFIODevice *vbasedev, Error **errp);
>>> +int vfio_attach_device(char *name, VFIODevice *vbasedev,
>>> +                       AddressSpace *as, Error **errp);
>>> +void vfio_detach_device(VFIODevice *vbasedev);
>>>
>>>  int vfio_kvm_device_add_fd(int fd, Error **errp);
>>>  int vfio_kvm_device_del_fd(int fd, Error **errp);
>>> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
>>> index 959b1362bb..7f3798b152 100644
>>> --- a/hw/vfio/common.c
>>> +++ b/hw/vfio/common.c
>>> @@ -2611,3 +2611,71 @@ int vfio_eeh_as_op(AddressSpace *as, uint32_t op)
>>>      }
>>>      return vfio_eeh_container_op(container, op);
>>>  }
>>> +
>>> +static int vfio_device_groupid(VFIODevice *vbasedev, Error **errp)
>>> +{
>>> +    char *tmp, group_path[PATH_MAX], *group_name;
>>> +    int ret, groupid;
>>> +    ssize_t len;
>>> +
>>> +    tmp = g_strdup_printf("%s/iommu_group", vbasedev->sysfsdev);
>>> +    len = readlink(tmp, group_path, sizeof(group_path));
>>> +    g_free(tmp);
>>> +
>>> +    if (len <= 0 || len >= sizeof(group_path)) {
>>> +        ret = len < 0 ? -errno : -ENAMETOOLONG;
>>> +        error_setg_errno(errp, -ret, "no iommu_group found");
>>> +        return ret;
>>> +    }
>>> +
>>> +    group_path[len] = 0;
>>> +
>>> +    group_name = basename(group_path);
>>> +    if (sscanf(group_name, "%d", &groupid) != 1) {
>>> +        error_setg_errno(errp, errno, "failed to read %s", group_path);
>>> +        return -errno;
>>> +    }
>>> +    return groupid;
>>> +}
>>> +
>>> +int vfio_attach_device(char *name, VFIODevice *vbasedev,
>>> +                       AddressSpace *as, Error **errp)
>>> +{
>>> +    int groupid = vfio_device_groupid(vbasedev, errp);
>>> +    VFIODevice *vbasedev_iter;
>>> +    VFIOGroup *group;
>>> +    int ret;
>>> +
>>> +    if (groupid < 0) {
>>> +        return groupid;
>>> +    }
>>> +
>>> +    trace_vfio_attach_device(vbasedev->name, groupid);
>>> +
>>> +    group = vfio_get_group(groupid, as, errp);
>>> +    if (!group) {
>>> +        return -ENOENT;
>>> +    }
>>> +
>>> +    QLIST_FOREACH(vbasedev_iter, &group->device_list, next) {
>>> +        if (strcmp(vbasedev_iter->name, vbasedev->name) == 0) {
>>> +            error_setg(errp, "device is already attached");
>>> +            vfio_put_group(group);
>>> +            return -EBUSY;
>>> +        }
>>> +    }
>>> +    ret = vfio_get_device(group, name, vbasedev, errp);
>>> +    if (ret) {
>>> +        vfio_put_group(group);
>>> +    }
>>> +
>>> +    return ret;
>>> +}
>>> +
>>> +void vfio_detach_device(VFIODevice *vbasedev)
>>> +{
>>> +    VFIOGroup *group = vbasedev->group;
>>> +
>>> +    vfio_put_base_device(vbasedev);
>>> +    vfio_put_group(group);
>>> +}
>>> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
>>> index 3b2ca3c24c..fe56789893 100644
>>> --- a/hw/vfio/pci.c
>>> +++ b/hw/vfio/pci.c
>>> @@ -2828,10 +2828,10 @@ static void vfio_populate_device(VFIOPCIDevice
>> *vdev, Error **errp)
>>>  static void vfio_put_device(VFIOPCIDevice *vdev)
>>>  {
>>> +    vfio_detach_device(&vdev->vbasedev);
>>> +
>>>      g_free(vdev->vbasedev.name);
>>>      g_free(vdev->msix);
>>> -
>>> -    vfio_put_base_device(&vdev->vbasedev);
>>>  }
>>>
>>>  static void vfio_err_notifier_handler(void *opaque)
>>> @@ -2978,13 +2978,9 @@ static void vfio_realize(PCIDevice *pdev, Error
>> **errp)
>>>  {
>>>      VFIOPCIDevice *vdev = VFIO_PCI(pdev);
>>>      VFIODevice *vbasedev = &vdev->vbasedev;
>>> -    VFIODevice *vbasedev_iter;
>>> -    VFIOGroup *group;
>>> -    char *tmp, *subsys, group_path[PATH_MAX], *group_name;
>>> +    char *tmp, *subsys;
>>>      Error *err = NULL;
>>> -    ssize_t len;
>>>      struct stat st;
>>> -    int groupid;
>>>      int i, ret;
>>>      bool is_mdev;
>>>      char uuid[UUID_FMT_LEN];
>>> @@ -3015,39 +3011,6 @@ static void vfio_realize(PCIDevice *pdev, Error
>> **errp)
>>>      vbasedev->type = VFIO_DEVICE_TYPE_PCI;
>>>      vbasedev->dev = DEVICE(vdev);
>>>
>>> -    tmp = g_strdup_printf("%s/iommu_group", vbasedev->sysfsdev);
>>> -    len = readlink(tmp, group_path, sizeof(group_path));
>>> -    g_free(tmp);
>>> -
>>> -    if (len <= 0 || len >= sizeof(group_path)) {
>>> -        error_setg_errno(errp, len < 0 ? errno : ENAMETOOLONG,
>>> -                         "no iommu_group found");
>>> -        goto error;
>>> -    }
>>> -
>>> -    group_path[len] = 0;
>>> -
>>> -    group_name = basename(group_path);
>>> -    if (sscanf(group_name, "%d", &groupid) != 1) {
>>> -        error_setg_errno(errp, errno, "failed to read %s", group_path);
>>> -        goto error;
>>> -    }
>>> -
>>> -    trace_vfio_realize(vbasedev->name, groupid);
>>> -
>>> -    group = vfio_get_group(groupid, pci_device_iommu_address_space(pdev),
>> errp);
>>> -    if (!group) {
>>> -        goto error;
>>> -    }
>>> -
>>> -    QLIST_FOREACH(vbasedev_iter, &group->device_list, next) {
>>> -        if (strcmp(vbasedev_iter->name, vbasedev->name) == 0) {
>>> -            error_setg(errp, "device is already attached");
>>> -            vfio_put_group(group);
>>> -            goto error;
>>> -        }
>>> -    }
>>> -
>>>      /*
>>>       * Mediated devices *might* operate compatibly with discarding of RAM, but
>>>       * we cannot know for certain, it depends on whether the mdev vendor
>> driver
>>> @@ -3065,7 +3028,6 @@ static void vfio_realize(PCIDevice *pdev, Error **errp)
>>>      if (vbasedev->ram_block_discard_allowed && !is_mdev) {
>>>          error_setg(errp, "x-balloon-allowed only potentially compatible "
>>>                     "with mdev devices");
>>> -        vfio_put_group(group);
>>>          goto error;
>>>      }
>>>
>>> @@ -3076,10 +3038,10 @@ static void vfio_realize(PCIDevice *pdev, Error
>> **errp)
>>>          name = g_strdup(vbasedev->name);
>>>      }
>>>
>>> -    ret = vfio_get_device(group, name, vbasedev, errp);
>>> +    ret = vfio_attach_device(name, vbasedev,
>>> +                             pci_device_iommu_address_space(pdev), errp);
>>>      g_free(name);
>>>      if (ret) {
>>> -        vfio_put_group(group);
>> independently on this patch, I think in case of error we leak
>> vbasedev->name. Please have a look and if confirmed you can send a
>> separate patch.
> In case of error, vbasedev->name is freed in vfio_put_device().
called in vfio_instance_finalize only. See comment below
>
>> Also I think if any subsequent action fail we shoudl properly detach the
>> detach the device so introduce an extra error goto label, my bad sorry.
> vfio_detach_device is called in vfio_instance_finalize(), this is just to follow
> the old code, group and container resource allocated in vfio_realize() are
> freed in vfio_instance_finalize().
>
> I agree this is strange, but I guess there may be some reason I'm unclear.
Yeah but if vfio_realize does fail, I am not sure the
vfio_instance_finalize gets called

Eric
>
> Thanks
> Zhenzhong
>