Re: [Qemu-devel] [PATCH v4 04/12] spapr vfio: add vfio_container_spapr_get_info()

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 09/06/2013 05:01 AM, Alex Williamson wrote:
> On Fri, 2013-08-30 at 20:15 +1000, Alexey Kardashevskiy wrote:
>> As sPAPR platform supports DMA windows on a PCI bus, the information
>> about their location and size should be passed into the guest via
>> the device tree.
>>
>> The patch adds a helper to read this info from the container fd.
>>
>> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
>> ---
>> Changes:
>> v4:
>> * fixed possible leaks on error paths
>> ---
>>  hw/misc/vfio.c         | 45 +++++++++++++++++++++++++++++++++++++++++++++
>>  include/hw/misc/vfio.h | 11 +++++++++++
>>  2 files changed, 56 insertions(+)
>>  create mode 100644 include/hw/misc/vfio.h
>>
>> diff --git a/hw/misc/vfio.c b/hw/misc/vfio.c
>> index 53791fb..4210471 100644
>> --- a/hw/misc/vfio.c
>> +++ b/hw/misc/vfio.c
>> @@ -39,6 +39,7 @@
>>  #include "qemu/range.h"
>>  #include "sysemu/kvm.h"
>>  #include "sysemu/sysemu.h"
>> +#include "hw/misc/vfio.h"
>>  
>>  /* #define DEBUG_VFIO */
>>  #ifdef DEBUG_VFIO
>> @@ -3490,3 +3491,47 @@ static void register_vfio_pci_dev_type(void)
>>  }
>>  
>>  type_init(register_vfio_pci_dev_type)
>> +
>> +int vfio_container_spapr_get_info(AddressSpace *as, int32_t groupid,
>> +                                  struct vfio_iommu_spapr_tce_info *info,
>> +                                  int *group_fd)
>> +{
>> +    VFIOAddressSpace *space;
>> +    VFIOGroup *group;
>> +    VFIOContainer *container;
>> +    int ret, fd;
>> +
>> +    space = vfio_get_address_space(as);
>> +    if (!space) {
>> +        return -1;
>> +    }
>> +    group = vfio_get_group(groupid, space);
>> +    if (!group) {
>> +        goto put_as_exit;
>> +    }
>> +    container = group->container;
>> +    if (!group->container) {
>> +        goto put_group_exit;
>> +    }
>> +    fd = container->fd;
>> +    if (!ioctl(fd, VFIO_CHECK_EXTENSION, VFIO_SPAPR_TCE_IOMMU)) {
>> +        goto put_group_exit;
>> +    }
>> +    ret = ioctl(fd, VFIO_IOMMU_SPAPR_TCE_GET_INFO, info);
>> +    if (ret) {
>> +        error_report("vfio: failed to get iommu info for container: %s",
>> +                     strerror(errno));
>> +        goto put_group_exit;
>> +    }
>> +    *group_fd = group->fd;
> 
> The above gets don't actually increment a reference count, so copying
> the fd seems risky here.


If fd is gone while I am carrying it to my "external VFIO user" to call
kvmppc_vfio_group_get_external_user() on it, then the guest just shut
itself in a foot, no?
And I do not see how I would make it no risky, do you?


>> +
>> +    return 0;
>> +
>> +put_group_exit:
>> +    vfio_put_group(group);
>> +
>> +put_as_exit:
>> +    vfio_put_address_space(space);
> 
> But put_group calls disconnect_container which calls
> put_address_space... so it get's put twice.  The lack of symmetry
> already bites us with a bug.

True. This will be fixed by moving vfio_get_address_space() into
vfio_get_group().




-- 
Alexey