Re: [RFC 1/3] util/vfio-helpers: Collect IOVA reserved regions

[Auger Eric]

Hi Fam,

On 9/25/20 4:43 PM, Fam Zheng wrote:
> On 2020-09-25 15:48, Eric Auger wrote:
>> The IOVA allocator currently ignores host reserved regions.
>> As a result some chosen IOVAs may collide with some of them,
>> resulting in VFIO MAP_DMA errors later on. This happens on ARM
>> where the MSI reserved window quickly is encountered:
>> [0x8000000, 0x8100000]. since 5.4 kernel, VFIO returns the usable
>> IOVA regions. So let's enumerate them in the prospect to avoid
>> them, later on.
>>
>> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>> ---
>>  util/vfio-helpers.c | 75 +++++++++++++++++++++++++++++++++++++++++++--
>>  1 file changed, 73 insertions(+), 2 deletions(-)
>>
>> diff --git a/util/vfio-helpers.c b/util/vfio-helpers.c
>> index 583bdfb36f..8e91beba95 100644
>> --- a/util/vfio-helpers.c
>> +++ b/util/vfio-helpers.c
>> @@ -40,6 +40,11 @@ typedef struct {
>>      uint64_t iova;
>>  } IOVAMapping;
>>  
>> +struct IOVARange {
>> +    uint64_t start;
>> +    uint64_t end;
>> +};
>> +
>>  struct QEMUVFIOState {
>>      QemuMutex lock;
>>  
>> @@ -49,6 +54,8 @@ struct QEMUVFIOState {
>>      int device;
>>      RAMBlockNotifier ram_notifier;
>>      struct vfio_region_info config_region_info, bar_region_info[6];
>> +    struct IOVARange *usable_iova_ranges;
>> +    uint8_t nb_iova_ranges;
>>  
>>      /* These fields are protected by @lock */
>>      /* VFIO's IO virtual address space is managed by splitting into a few
>> @@ -236,6 +243,36 @@ static int qemu_vfio_pci_write_config(QEMUVFIOState *s, 
>> void *buf, int size, int
>>      return ret == size ? 0 : -errno;
>>  }
>>  
>> +static void collect_usable_iova_ranges(QEMUVFIOState *s, void *first_cap)
>> +{
>> +    struct vfio_iommu_type1_info_cap_iova_range *cap_iova_range;
>> +    struct vfio_info_cap_header *cap = first_cap;
>> +    void *offset = first_cap;
>> +    int i;
>> +
>> +    while (cap->id != VFIO_IOMMU_TYPE1_INFO_CAP_IOVA_RANGE) {
>> +        if (cap->next) {
> 
> This check looks reversed.
> 
>> +            return;
>> +        }
>> +        offset += cap->next;
> 
> @offset is unused.
> 
>> +        cap = (struct vfio_info_cap_header *)cap;
> 
> This assignment is nop.
ugh indeed, that loop implementation is totally crap. I will test the
rewriting by adding an extra cap on kernel side.
> 
>> +    }
>> +
>> +    cap_iova_range = (struct vfio_iommu_type1_info_cap_iova_range *)cap;
>> +
>> +    s->nb_iova_ranges = cap_iova_range->nr_iovas;
>> +    if (s->nb_iova_ranges > 1) {
>> +        s->usable_iova_ranges =
>> +            g_realloc(s->usable_iova_ranges,
>> +                      s->nb_iova_ranges * sizeof(struct IOVARange));
>> +    }
>> +
>> +    for (i = 0; i <  s->nb_iova_ranges; i++) {
> 
> s/  / /
ok
> 
>> +        s->usable_iova_ranges[i].start = 
>> cap_iova_range->iova_ranges[i].start;
>> +        s->usable_iova_ranges[i].end = cap_iova_range->iova_ranges[i].end;
>> +    }
>> +}
>> +
>>  static int qemu_vfio_init_pci(QEMUVFIOState *s, const char *device,
>>                                Error **errp)
>>  {
>> @@ -243,10 +280,13 @@ static int qemu_vfio_init_pci(QEMUVFIOState *s, const 
>> char *device,
>>      int i;
>>      uint16_t pci_cmd;
>>      struct vfio_group_status group_status = { .argsz = sizeof(group_status) 
>> };
>> -    struct vfio_iommu_type1_info iommu_info = { .argsz = sizeof(iommu_info) 
>> };
>> +    struct vfio_iommu_type1_info *iommu_info = NULL;
>> +    size_t iommu_info_size = sizeof(*iommu_info);
>>      struct vfio_device_info device_info = { .argsz = sizeof(device_info) };
>>      char *group_file = NULL;
>>  
>> +    s->usable_iova_ranges = NULL;
>> +
>>      /* Create a new container */
>>      s->container = open("/dev/vfio/vfio", O_RDWR);
>>  
>> @@ -310,13 +350,38 @@ static int qemu_vfio_init_pci(QEMUVFIOState *s, const 
>> char *device,
>>          goto fail;
>>      }
>>  
>> +    iommu_info = g_malloc0(iommu_info_size);
>> +    iommu_info->argsz = iommu_info_size;
>> +
>>      /* Get additional IOMMU info */
>> -    if (ioctl(s->container, VFIO_IOMMU_GET_INFO, &iommu_info)) {
>> +    if (ioctl(s->container, VFIO_IOMMU_GET_INFO, iommu_info)) {
>>          error_setg_errno(errp, errno, "Failed to get IOMMU info");
>>          ret = -errno;
>>          goto fail;
>>      }
>>  
>> +    /*
>> +     * if the kernel does not report usable IOVA regions, choose
>> +     * the legacy [QEMU_VFIO_IOVA_MIN, QEMU_VFIO_IOVA_MAX -1] region
>> +     */
>> +    s->nb_iova_ranges = 1;
>> +    s->usable_iova_ranges = g_new0(struct IOVARange, 1);
>> +    s->usable_iova_ranges[0].start = QEMU_VFIO_IOVA_MIN;
>> +    s->usable_iova_ranges[0].end = QEMU_VFIO_IOVA_MAX - 1;
>> +
>> +    if (iommu_info->argsz > iommu_info_size) {
>> +        void *first_cap;
>> +
>> +        iommu_info_size = iommu_info->argsz;
>> +        iommu_info = g_realloc(iommu_info, iommu_info_size);
>> +        if (ioctl(s->container, VFIO_IOMMU_GET_INFO, iommu_info)) {
>> +            ret = -errno;
>> +            goto fail;
>> +        }
>> +        first_cap = (void *)iommu_info + iommu_info->cap_offset;
>> +        collect_usable_iova_ranges(s, first_cap);
>> +    }
>> +
>>      s->device = ioctl(s->group, VFIO_GROUP_GET_DEVICE_FD, device);
>>  
>>      if (s->device < 0) {
>> @@ -365,8 +430,12 @@ static int qemu_vfio_init_pci(QEMUVFIOState *s, const 
>> char *device,
>>      if (ret) {
>>          goto fail;
>>      }
>> +    g_free(iommu_info);
>>      return 0;
>>  fail:
>> +    g_free(s->usable_iova_ranges);
> 
> Set s->usable_iova_ranges to NULL to avoid double free?
I think I did at the beginning of qemu_vfio_init_pci()

Thanks

Eric
> 
>> +    s->nb_iova_ranges = 0;
>> +    g_free(iommu_info);
>>      close(s->group);
>>  fail_container:
>>      close(s->container);
>> @@ -716,6 +785,8 @@ void qemu_vfio_close(QEMUVFIOState *s)
>>          qemu_vfio_undo_mapping(s, &s->mappings[i], NULL);
>>      }
>>      ram_block_notifier_remove(&s->ram_notifier);
>> +    g_free(s->usable_iova_ranges);
>> +    s->nb_iova_ranges = 0;
>>      qemu_vfio_reset(s);
>>      close(s->device);
>>      close(s->group);
>> -- 
>> 2.21.3
>>
>>
> 
> Fam
>