Re: [PATCH RFC v2 08/16] vfio-user: get region info

[John Johnson]

> On Sep 7, 2021, at 7:31 AM, Stefan Hajnoczi <stefanha@redhat.com> wrote:
> 
> On Mon, Aug 16, 2021 at 09:42:41AM -0700, Elena Ufimtseva wrote:
>> @@ -1514,6 +1515,16 @@ bool vfio_get_info_dma_avail(struct 
>> vfio_iommu_type1_info *info,
>>     return true;
>> }
>> 
>> +static int vfio_get_region_info_remfd(VFIODevice *vbasedev, int index)
>> +{
>> +    struct vfio_region_info *info;
>> +
>> +    if (vbasedev->regions == NULL || vbasedev->regions[index] == NULL) {
>> +        vfio_get_region_info(vbasedev, index, &info);
>> +    }
> 
> Maybe this will be called from other places in the future, but the
> vfio_region_setup() caller below already invoked vfio_get_region_info()
> so I'm not sure it's necessary to do this again?
> 
> Perhaps add an int *remfd argument to vfio_get_region_info(). That way
> vfio_get_region_info_remfd() isn't necessary.
> 

        I think they could be combined, but the region capabilities are
retrieved with separate calls to vfio_get_region_info_cap(), so I followed
that precedent.


>> @@ -2410,6 +2442,24 @@ int vfio_get_region_info(VFIODevice *vbasedev, int 
>> index,
>>                          struct vfio_region_info **info)
>> {
>>     size_t argsz = sizeof(struct vfio_region_info);
>> +    int fd = -1;
>> +    int ret;
>> +
>> +    /* create region cache */
>> +    if (vbasedev->regions == NULL) {
>> +        vbasedev->regions = g_new0(struct vfio_region_info *,
>> +                                   vbasedev->num_regions);
>> +        if (vbasedev->proxy != NULL) {
>> +            vbasedev->regfds = g_new0(int, vbasedev->num_regions);
>> +        }
>> +    }
>> +    /* check cache */
>> +    if (vbasedev->regions[index] != NULL) {
>> +        *info = g_malloc0(vbasedev->regions[index]->argsz);
>> +        memcpy(*info, vbasedev->regions[index],
>> +               vbasedev->regions[index]->argsz);
>> +        return 0;
>> +    }
> 
> Why is it necessary to introduce a cache? Is it to avoid passing the
> same fd multiple times?
> 

        Yes.  For polled regions, the server returns an FD with each
message, so there would be an FD leak if I didn’t check that the region
hadn’t already returned one.  Since I had to cache the FD anyway, I
cached the whole struct.


>> 
>>     *info = g_malloc0(argsz);
>> 
>> @@ -2417,7 +2467,17 @@ int vfio_get_region_info(VFIODevice *vbasedev, int 
>> index,
>> retry:
>>     (*info)->argsz = argsz;
>> 
>> -    if (ioctl(vbasedev->fd, VFIO_DEVICE_GET_REGION_INFO, *info)) {
>> +    if (vbasedev->proxy != NULL) {
>> +        VFIOUserFDs fds = { 0, 1, &fd};
>> +
>> +        ret = vfio_user_get_region_info(vbasedev, index, *info, &fds);
>> +    } else {
>> +        ret = ioctl(vbasedev->fd, VFIO_DEVICE_GET_REGION_INFO, *info);
>> +        if (ret < 0) {
>> +            ret = -errno;
>> +        }
>> +    }
>> +    if (ret != 0) {
>>         g_free(*info);
>>         *info = NULL;
>>         return -errno;
>> @@ -2426,10 +2486,22 @@ retry:
>>     if ((*info)->argsz > argsz) {
>>         argsz = (*info)->argsz;
>>         *info = g_realloc(*info, argsz);
>> +        if (fd != -1) {
>> +            close(fd);
>> +            fd = -1;
>> +        }
>> 
>>         goto retry;
>>     }
>> 
>> +    /* fill cache */
>> +    vbasedev->regions[index] = g_malloc0(argsz);
>> +    memcpy(vbasedev->regions[index], *info, argsz);
>> +    *vbasedev->regions[index] = **info;
> 
> The previous line already copied the contents of *info. What is the
> purpose of this assignment?
> 

        That might be a mis-merge.  The struct assignment was a bug
fixed several revs ago with the memcpy() call.


>> +    if (vbasedev->regfds != NULL) {
>> +        vbasedev->regfds[index] = fd;
>> +    }
>> +
>>     return 0;
>> }
>> 
>> diff --git a/hw/vfio/user.c b/hw/vfio/user.c
>> index b584b8e0f2..91b51f37df 100644
>> --- a/hw/vfio/user.c
>> +++ b/hw/vfio/user.c
>> @@ -734,3 +734,36 @@ int vfio_user_get_info(VFIODevice *vbasedev)
>>     vbasedev->reset_works = !!(msg.flags & VFIO_DEVICE_FLAGS_RESET);
>>     return 0;
>> }
>> +
>> +int vfio_user_get_region_info(VFIODevice *vbasedev, int index,
>> +                              struct vfio_region_info *info, VFIOUserFDs 
>> *fds)
>> +{
>> +    g_autofree VFIOUserRegionInfo *msgp = NULL;
>> +    int size;
> 
> Please use uint32_t size instead of int size to prevent possible
> signedness issues:
> - VFIOUserRegionInfo->argsz is uint32_t.
> - sizeof(VFIOUserHdr) is size_t.
> - The vfio_user_request_msg() size argument is uint32_t.

        OK

                JJ