Re: [PATCH v3 04/10] vfio/iommufd: Introduce auto domain creation

[Joao Martins]

On 09/07/2024 07:50, Cédric Le Goater wrote:
> On 7/8/24 4:34 PM, 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
>> 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(). If this fails (i.e. mdevs) it falls back
>> to IOAS attach (which again is always the case for mdevs).
>>
>> 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
>> 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' 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      |  4 ++
>>   backends/iommufd.c            | 29 +++++++++++
>>   hw/vfio/iommufd.c             | 91 +++++++++++++++++++++++++++++++++++
>>   backends/trace-events         |  1 +
>>   5 files changed, 134 insertions(+)
>>
>> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
>> index e8ddf92bb185..82c5a4aaa61e 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);
>> @@ -134,6 +141,8 @@ 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..35a8cec9780f 100644
>> --- a/include/sysemu/iommufd.h
>> +++ b/include/sysemu/iommufd.h
>> @@ -50,6 +50,10 @@ 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);
>> +int 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);
>>     #define TYPE_HOST_IOMMU_DEVICE_IOMMUFD TYPE_HOST_IOMMU_DEVICE "-iommufd"
>>   #endif
>> diff --git a/backends/iommufd.c b/backends/iommufd.c
>> index 2b3d51af26d2..f5f73eaf4a1a 100644
>> --- a/backends/iommufd.c
>> +++ b/backends/iommufd.c
>> @@ -208,6 +208,35 @@ int iommufd_backend_unmap_dma(IOMMUFDBackend *be,
>> uint32_t ioas_id,
>>       return ret;
>>   }
>>   +int 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)
>> +{
>> +    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) {
>> +        ret = -errno;
>> +        error_report("IOMMU_HWPT_ALLOC failed: %m");
> 
> Please add an 'Error **errp' parameter.
> 

Yes, but I need to do some special casing for mdev then. I'll expand below.

>> +    } else {
>> +        *out_hwpt = alloc_hwpt.out_hwpt_id;
>> +    }
>> +    return ret;
>> +}
>> +
>>   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 5a5993b17c2e..2ca9a32cc7b6 100644
>> --- a/hw/vfio/iommufd.c
>> +++ b/hw/vfio/iommufd.c
>> @@ -212,10 +212,95 @@ 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, NULL);
>> +        if (ret) {
>> +            /* -EINVAL means the domain is incompatible with the device. */
>> +            if (ret == -EINVAL) {
>> +                continue;
>> +            }
> 
> We should propagate an error in the false case.
> 
Same as before due to mdev.

When we are dealing with physical devices this is correct to handle as an error
and stops the attach. However we may still get a -ENOENT for mdevs which is why
I wasn't making an error here.

It just so seems confusing that all the code tries not to special case mdev,
that I went along with it. But honestly on a second look I should really special
case mdev to avoid autodomains given that we know it will fail. This way I
should be able to propagate all errors causes and not wrongly hide errors that
might be applicable for physical devices.

Now the -EINVAL is not an error we are supposed to propagate, as we expect
-EINVAL as a 'this domain can't be used try the next one'.

>> +            return false;
>> +        } else {
>> +            vbasedev->hwpt = hwpt;
>> +            QLIST_INSERT_HEAD(&hwpt->device_list, vbasedev, hwpt_next);
>> +            return true;
>> +        }
>> +    }
>> +
>> +    ret = iommufd_backend_alloc_hwpt(iommufd,
>> +                                     vbasedev->devid,
>> +                                     container->ioas_id, flags,
>> +                                     IOMMU_HWPT_DATA_NONE, 0, NULL, 
>> &hwpt_id);
>> +    if (ret) {
>> +        /*
>> +         * When there's no domains allocated we can still attempt a hardware
>> +         * pagetable allocation for an mdev, which ends up returning -ENOENT
>> +         * This is benign and meant to fallback into IOAS attach, hence 
>> don't
>> +         * set errp.
>> +         */
> 
> same here.
> 
As the comment says the previous paragraph was the reason for not propagating an
error here.

>> +        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);
>> +    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)
>>   {
>> +    if (iommufd_cdev_autodomains_get(vbasedev, container, errp)) {
>> +        return true;
>> +    }
>> +
>> +    /*
>> +     * iommufd_cdev_autodomains_get() may have an expected failure (-ENOENT)
>> +     * for mdevs as they aren't real physical devices. @errp is only set
>> +     * when real failures happened i.e. failing to attach to a newly created
>> +     * hardware pagetable. These are fatal and should fail the attachment.
>> +     */
>> +    if (*errp) {
>> +        return false;
>> +    }
>> +
>>       return !iommufd_cdev_attach_ioas_hwpt(vbasedev, container->ioas_id, 
>> errp);
>>   }
>>   @@ -224,6 +309,11 @@ static void iommufd_cdev_detach_container(VFIODevice
>> *vbasedev,
>>   {
>>       Error *err = NULL;
>>   +    if (vbasedev->hwpt) {
>> +        iommufd_cdev_autodomains_put(vbasedev, container);
>> +        return;
>> +    }
>> +
>>       if (!iommufd_cdev_detach_ioas_hwpt(vbasedev, &err)) {
>>           error_report_err(err);
>>       }
>> @@ -354,6 +444,7 @@ static bool iommufd_cdev_attach(const char *name,
>> VFIODevice *vbasedev,
>>       container = VFIO_IOMMU_IOMMUFD(object_new(TYPE_VFIO_IOMMU_IOMMUFD));
>>       container->be = vbasedev->iommufd;
>>       container->ioas_id = ioas_id;
>> +    QLIST_INIT(&container->hwpt_list);
>>         bcontainer = &container->bcontainer;
>>       vfio_address_space_insert(space, bcontainer);
>> diff --git a/backends/trace-events b/backends/trace-events
>> index 211e6f374adc..4d8ac02fe7d6 100644
>> --- a/backends/trace-events
>> +++ b/backends/trace-events
>> @@ -14,4 +14,5 @@ iommufd_backend_map_dma(int iommufd, uint32_t ioas, 
>> uint64_t
>> iova, uint64_t size
>>   iommufd_backend_unmap_dma_non_exist(int iommufd, uint32_t ioas, uint64_t
>> iova, uint64_t size, int ret) " Unmap nonexistent mapping: iommufd=%d ioas=%d
>> iova=0x%"PRIx64" size=0x%"PRIx64" (%d)"
>>   iommufd_backend_unmap_dma(int iommufd, uint32_t ioas, uint64_t iova,
>> uint64_t size, int ret) " iommufd=%d ioas=%d iova=0x%"PRIx64" 
>> size=0x%"PRIx64"
>> (%d)"
>>   iommufd_backend_alloc_ioas(int iommufd, uint32_t ioas) " iommufd=%d 
>> ioas=%d"
>> +iommufd_backend_alloc_hwpt(int iommufd, uint32_t dev_id, uint32_t pt_id,
>> uint32_t flags, uint32_t hwpt_type, uint32_t len, uint64_t data_ptr, uint32_t
>> out_hwpt_id, int ret) " iommufd=%d dev_id=%u pt_id=%u flags=0x%x hwpt_type=%u
>> len=%u data_ptr=0x%"PRIx64" out_hwpt=%u (%d)"
>>   iommufd_backend_free_id(int iommufd, uint32_t id, int ret) " iommufd=%d
>> id=%d (%d)"
>