Re: [PATCH v4 05/12] vfio/iommufd: Introduce auto domain creation

[Joao Martins <joao.m.martins@oracle.com>]

On 17/07/2024 03:52, Duan, Zhenzhong wrote:
> 
> 
>> -----Original Message-----
>> From: Joao Martins <joao.m.martins@oracle.com>
>> Subject: Re: [PATCH v4 05/12] vfio/iommufd: Introduce auto domain
>> creation
>>
>> On 16/07/2024 17:44, Joao Martins wrote:
>>> On 16/07/2024 17:04, Eric Auger wrote:
>>>> Hi Joao,
>>>>
>>>> On 7/12/24 13:46, Joao Martins wrote:
>>>>> There's generally two modes of operation for IOMMUFD:
>>>>>
>>>>> * The simple user API which intends to perform relatively simple things
>>>>> with IOMMUs e.g. DPDK. It generally creates an IOAS and attach to VFIO
>>>>
>>>> It generally creates? can you explicit what is "it"
>>>>
>>> 'It' here refers to the process/API-user
>>>
>>>> I am confused by this automatic terminology again (not your fault). the
>> doc says:
>>>> "
>>>>
>>>>   *
>>>>
>>>>     Automatic domain - refers to an iommu domain created automatically
>>>>     when attaching a device to an IOAS object. This is compatible to the
>>>>     semantics of VFIO type1.
>>>>
>>>>   *
>>>>
>>>>     Manual domain - refers to an iommu domain designated by the user as
>>>>     the target pagetable to be attached to by a device. Though currently
>>>>     there are no uAPIs to directly create such domain, the datastructure
>>>>     and algorithms are ready for handling that use case.
>>>>
>>>> "
>>>>
>>>>
>>>> in 1) the device is attached to the ioas id (using the auto domain if I am
>> not wrong)
>>>> Here you attach to an hwpt id. Isn't it a manual domain?
>>>>
>>>
>>> Correct.
>>>
>>> The 'auto domains' generally refers to the kernel-equivalent own
>> automatic
>>> attaching to a new pagetable.
>>>
>>> Here I call 'auto domains' in the userspace version too because we are
>> doing the
>>> exact same but from userspace, using the manual API in IOMMUFD.
>>>
>>>>> and mainly performs IOAS_MAP and UNMAP.
>>>>>
>>>>> * The native IOMMUFD API where you have fine grained control of the
>>>>> IOMMU domain and model it accordingly. This is where most new
>> feature
>>>>> are being steered to.
>>>>>
>>>>> For dirty tracking 2) is required, as it needs to ensure that
>>>>> the stage-2/parent IOMMU domain will only attach devices
>>>>> that support dirty tracking (so far it is all homogeneous in x86, likely
>>>>> not the case for smmuv3). Such invariant on dirty tracking provides a
>>>>> useful guarantee to VMMs that will refuse incompatible device
>>>>> attachments for IOMMU domains.
>>>>>
>>>>> Dirty tracking insurance is enforced via HWPT_ALLOC, which is
>>>>> responsible for creating an IOMMU domain. This is contrast to the
>>>>> 'simple API' where the IOMMU domain is created by IOMMUFD
>> automatically
>>>>> when it attaches to VFIO (usually referred as autodomains) but it has
>>>>> the needed handling for mdevs.
>>>>>
>>>>> To support dirty tracking with the advanced IOMMUFD API, it needs
>>>>> similar logic, where IOMMU domains are created and devices attached
>> to
>>>>> compatible domains. Essentially mimmicing kernel
>>>>> iommufd_device_auto_get_domain(). With mdevs given there's no
>> IOMMU domain
>>>>> it falls back to IOAS attach.
>>>>>
>>>>> The auto domain logic allows different IOMMU domains to be created
>> when
>>>>> DMA dirty tracking is not desired (and VF can provide it), and others
>> where
>>>>> it is. Here is not used in this way here given how VFIODevice migration
>>>>
>>>> Here is not used in this way here ?
>>>>
>>>
>>> I meant, 'Here it is not used in this way given (...)'
>>>
>>>>> state is initialized after the device attachment. But such mixed mode of
>>>>> IOMMU dirty tracking + device dirty tracking is an improvement that
>> can
>>>>> be added on. Keep the 'all of nothing' of type1 approach that we have
>>>>> been using so far between container vs device dirty tracking.
>>>>>
>>>>> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
>>>>> ---
>>>>>  include/hw/vfio/vfio-common.h |  9 ++++
>>>>>  include/sysemu/iommufd.h      |  5 +++
>>>>>  backends/iommufd.c            | 30 +++++++++++++
>>>>>  hw/vfio/iommufd.c             | 82
>> +++++++++++++++++++++++++++++++++++
>>>>>  backends/trace-events         |  1 +
>>>>>  5 files changed, 127 insertions(+)
>>>>>
>>>>> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-
>> common.h
>>>>> index 7419466bca92..2dd468ce3c02 100644
>>>>> --- a/include/hw/vfio/vfio-common.h
>>>>> +++ b/include/hw/vfio/vfio-common.h
>>>>> @@ -95,10 +95,17 @@ typedef struct VFIOHostDMAWindow {
>>>>>
>>>>>  typedef struct IOMMUFDBackend IOMMUFDBackend;
>>>>>
>>>>> +typedef struct VFIOIOASHwpt {
>>>>> +    uint32_t hwpt_id;
>>>>> +    QLIST_HEAD(, VFIODevice) device_list;
>>>>> +    QLIST_ENTRY(VFIOIOASHwpt) next;
>>>>> +} VFIOIOASHwpt;
>>>>> +
>>>>>  typedef struct VFIOIOMMUFDContainer {
>>>>>      VFIOContainerBase bcontainer;
>>>>>      IOMMUFDBackend *be;
>>>>>      uint32_t ioas_id;
>>>>> +    QLIST_HEAD(, VFIOIOASHwpt) hwpt_list;
>>>>>  } VFIOIOMMUFDContainer;
>>>>>
>>>>>  OBJECT_DECLARE_SIMPLE_TYPE(VFIOIOMMUFDContainer,
>> VFIO_IOMMU_IOMMUFD);
>>>>> @@ -135,6 +142,8 @@ typedef struct VFIODevice {
>>>>>      HostIOMMUDevice *hiod;
>>>>>      int devid;
>>>>>      IOMMUFDBackend *iommufd;
>>>>> +    VFIOIOASHwpt *hwpt;
>>>>> +    QLIST_ENTRY(VFIODevice) hwpt_next;
>>>>>  } VFIODevice;
>>>>>
>>>>>  struct VFIODeviceOps {
>>>>> diff --git a/include/sysemu/iommufd.h b/include/sysemu/iommufd.h
>>>>> index 57d502a1c79a..e917e7591d05 100644
>>>>> --- a/include/sysemu/iommufd.h
>>>>> +++ b/include/sysemu/iommufd.h
>>>>> @@ -50,6 +50,11 @@ int
>> iommufd_backend_unmap_dma(IOMMUFDBackend *be, uint32_t ioas_id,
>>>>>  bool iommufd_backend_get_device_info(IOMMUFDBackend *be,
>> uint32_t devid,
>>>>>                                       uint32_t *type, void *data, uint32_t len,
>>>>>                                       uint64_t *caps, Error **errp);
>>>>> +bool iommufd_backend_alloc_hwpt(IOMMUFDBackend *be, uint32_t
>> dev_id,
>>>>> +                                uint32_t pt_id, uint32_t flags,
>>>>> +                                uint32_t data_type, uint32_t data_len,
>>>>> +                                void *data_ptr, uint32_t *out_hwpt,
>>>>> +                                Error **errp);
>>>>>
>>>>>  #define TYPE_HOST_IOMMU_DEVICE_IOMMUFD
>> TYPE_HOST_IOMMU_DEVICE "-iommufd"
>>>>>  #endif
>>>>> diff --git a/backends/iommufd.c b/backends/iommufd.c
>>>>> index 2b3d51af26d2..5d3dfa917415 100644
>>>>> --- a/backends/iommufd.c
>>>>> +++ b/backends/iommufd.c
>>>>> @@ -208,6 +208,36 @@ int
>> iommufd_backend_unmap_dma(IOMMUFDBackend *be, uint32_t ioas_id,
>>>>>      return ret;
>>>>>  }
>>>>>
>>>>> +bool iommufd_backend_alloc_hwpt(IOMMUFDBackend *be, uint32_t
>> dev_id,
>>>>> +                                uint32_t pt_id, uint32_t flags,
>>>>> +                                uint32_t data_type, uint32_t data_len,
>>>>> +                                void *data_ptr, uint32_t *out_hwpt,
>>>>> +                                Error **errp)
>>>>> +{
>>>>> +    int ret, fd = be->fd;
>>>>> +    struct iommu_hwpt_alloc alloc_hwpt = {
>>>>> +        .size = sizeof(struct iommu_hwpt_alloc),
>>>>> +        .flags = flags,
>>>>> +        .dev_id = dev_id,
>>>>> +        .pt_id = pt_id,
>>>>> +        .data_type = data_type,
>>>>> +        .data_len = data_len,
>>>>> +        .data_uptr = (uint64_t)data_ptr,
>>>>> +    };
>>>>> +
>>>>> +    ret = ioctl(fd, IOMMU_HWPT_ALLOC, &alloc_hwpt);
>>>>> +    trace_iommufd_backend_alloc_hwpt(fd, dev_id, pt_id, flags,
>> data_type,
>>>>> +                                     data_len, (uint64_t)data_ptr,
>>>>> +                                     alloc_hwpt.out_hwpt_id, ret);
>>>>> +    if (ret) {
>>>>> +        error_setg_errno(errp, errno, "Failed to allocate hwpt");
>>>>> +        return false;
>>>>> +    }
>>>>> +
>>>>> +    *out_hwpt = alloc_hwpt.out_hwpt_id;
>>>>> +    return true;
>>>>> +}
>>>>> +
>>>>>  bool iommufd_backend_get_device_info(IOMMUFDBackend *be,
>> uint32_t devid,
>>>>>                                       uint32_t *type, void *data, uint32_t len,
>>>>>                                       uint64_t *caps, Error **errp)
>>>>> diff --git a/hw/vfio/iommufd.c b/hw/vfio/iommufd.c
>>>>> index 077dea8f1b64..325c7598d5a1 100644
>>>>> --- a/hw/vfio/iommufd.c
>>>>> +++ b/hw/vfio/iommufd.c
>>>>> @@ -212,10 +212,86 @@ static bool
>> iommufd_cdev_detach_ioas_hwpt(VFIODevice *vbasedev, Error **errp)
>>>>>      return true;
>>>>>  }
>>>>>
>>>>> +static bool iommufd_cdev_autodomains_get(VFIODevice *vbasedev,
>>>>> +                                         VFIOIOMMUFDContainer *container,
>>>>> +                                         Error **errp)
>>>>> +{
>>>>> +    IOMMUFDBackend *iommufd = vbasedev->iommufd;
>>>>> +    uint32_t flags = 0;
>>>>> +    VFIOIOASHwpt *hwpt;
>>>>> +    uint32_t hwpt_id;
>>>>> +    int ret;
>>>>> +
>>>>> +    /* Try to find a domain */
>>>>> +    QLIST_FOREACH(hwpt, &container->hwpt_list, next) {
>>>>> +        ret = iommufd_cdev_attach_ioas_hwpt(vbasedev, hwpt->hwpt_id,
>> errp);
>>>>> +        if (ret) {
>>>>> +            /* -EINVAL means the domain is incompatible with the device.
>> */
>>>>> +            if (ret == -EINVAL) {
>>>>> +                /*
>>>>> +                 * It is an expected failure and it just means we will try
>>>>> +                 * another domain, or create one if no existing compatible
>>>>> +                 * domain is found. Hence why the error is discarded below.
>>>>> +                 */
>>>>> +                error_free(*errp);
>>>>> +                *errp = NULL;
>>>>> +                continue;
>>>>> +            }
>>>>> +
>>>>> +            return false;
>>>>> +        } else {
>>>>> +            vbasedev->hwpt = hwpt;
>>>>> +            QLIST_INSERT_HEAD(&hwpt->device_list, vbasedev, hwpt_next);
>>>>> +            return true;
>>>>> +        }
>>>>> +    }
>>>>> +
>>>>> +    if (!iommufd_backend_alloc_hwpt(iommufd, vbasedev->devid,
>>>>> +                                    container->ioas_id, flags,
>>>>> +                                    IOMMU_HWPT_DATA_NONE, 0, NULL,
>>>>> +                                    &hwpt_id, errp)) {
>>>>> +        return false;
>>>>> +    }
>>>>> +
>>>>> +    hwpt = g_malloc0(sizeof(*hwpt));
>>>>> +    hwpt->hwpt_id = hwpt_id;
>>>>> +    QLIST_INIT(&hwpt->device_list);
>>>>> +
>>>>> +    ret = iommufd_cdev_attach_ioas_hwpt(vbasedev, hwpt->hwpt_id,
>> errp);
>>>>> +    if (ret) {
>>>>> +        iommufd_backend_free_id(container->be, hwpt->hwpt_id);
>>>>> +        g_free(hwpt);
>>>>> +        return false;
>>>>> +    }
>>>>> +
>>>>> +    vbasedev->hwpt = hwpt;
>>>>> +    QLIST_INSERT_HEAD(&hwpt->device_list, vbasedev, hwpt_next);
>>>>> +    QLIST_INSERT_HEAD(&container->hwpt_list, hwpt, next);
>>>>> +    return true;
>>>>> +}
>>>>> +
>>>>> +static void iommufd_cdev_autodomains_put(VFIODevice *vbasedev,
>>>>> +                                         VFIOIOMMUFDContainer *container)
>>>>> +{
>>>>> +    VFIOIOASHwpt *hwpt = vbasedev->hwpt;
>>>>> +
>>>>> +    QLIST_REMOVE(vbasedev, hwpt_next);
>>>> don't you want to reset vbasedev->hwpt = NULL too?
>>>>
>>> Yeap, Thanks for catching that
>>>
>>>>
>>>>> +    if (QLIST_EMPTY(&hwpt->device_list)) {
>>>>> +        QLIST_REMOVE(hwpt, next);
>>>>> +        iommufd_backend_free_id(container->be, hwpt->hwpt_id);
>>>>> +        g_free(hwpt);
>>>>> +    }
>>>>> +}
>>>>> +
>>>>>  static bool iommufd_cdev_attach_container(VFIODevice *vbasedev,
>>>>>                                            VFIOIOMMUFDContainer *container,
>>>>>                                            Error **errp)
>>>>>  {
>>>>> +    /* mdevs aren't physical devices and will fail with auto domains */
>>>>> +    if (!vbasedev->mdev) {
>>>>> +        return iommufd_cdev_autodomains_get(vbasedev, container,
>> errp);
>>>>> +    }
>>>>> +
>>>>>      return !iommufd_cdev_attach_ioas_hwpt(vbasedev, container-
>>> ioas_id, errp);
>>>>>  }
>>>>>
>>>>> @@ -224,6 +300,11 @@ static void
>> iommufd_cdev_detach_container(VFIODevice *vbasedev,
>>>>>  {
>>>>>      Error *err = NULL;
>>>>>
>>>>> +    if (vbasedev->hwpt) {
>>>>> +        iommufd_cdev_autodomains_put(vbasedev, container);
>>>>> +        return;
>>>> Where do we detach the device from the hwpt?
>>>>
>>> In iommufd_backend_free_id() for auto domains
>>>
>>
>> to clarify here I meant *userspace* auto domains
>>
>> *kernel* auto domains (mdev) goes via DETACH_IOMMUFD_PT
> 
> If the device is still attached to the hwpt, will iommufd_backend_free_id() succeed?
> Have you tried the hot unplug?
> 

I have but I didn't see any errors. But I will check again for v5 as it could
also be my oversight.

I was thinking about Eric's remark overnight and I think what I am doing is not
correct regardless of the above.

I should be calling DETACH_IOMMUFD_PT pairing with ATTACH_IOMMUFD_PT, and the
iommufd_backend_free_id() is to drop the final reference pairing with
alloc_hwpt() when the device list is empty i.e. when there's no more devices in
that vdev::hwpt.

DETACH_IOMMUFD_PT decrement the hwpt refcount and it doesn't differentiate
between auto domains vs manual domains.

The code is already there anyhow it just has the order of
iommufd_cdev_autodomains_put vs detach invocation reversed; I'll fix that for
next version.