Re: [PATCH 2/2] drivers/vfio: Support EEH error injection

Gavin Shan
2015-03-12T05:02:09Z

On Thu, Mar 12, 2015 at 03:21:29PM +1100, David Gibson wrote:
>On Thu, Mar 12, 2015 at 02:16:42PM +1100, Gavin Shan wrote:
>> On Thu, Mar 12, 2015 at 11:57:21AM +1100, David Gibson wrote:
>> >On Wed, Mar 11, 2015 at 05:34:11PM +1100, Gavin Shan wrote:
>> >> The patch adds one more EEH sub-command (VFIO_EEH_PE_INJECT_ERR)
>> >> to inject the specified EEH error, which is represented by
>> >> (struct vfio_eeh_pe_err), to the indicated PE for testing purpose.
>> >>
>> >> Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
>> >> ---
>> >> Documentation/vfio.txt | 47 ++++++++++++++++++++++++++++++-------------
>> >> drivers/vfio/vfio_spapr_eeh.c | 14 +++++++++++++
>> >> include/uapi/linux/vfio.h | 34 ++++++++++++++++++++++++++++++-
>> >> 3 files changed, 80 insertions(+), 15 deletions(-)
>> >>
>> >> diff --git a/Documentation/vfio.txt b/Documentation/vfio.txt
>> >> index 96978ec..2e7f736 100644
>> >> --- a/Documentation/vfio.txt
>> >> +++ b/Documentation/vfio.txt
>> >> @@ -328,7 +328,13 @@ So 4 additional ioctls have been added:
>> >>
>> >> The code flow from the example above should be slightly changed:
>> >>
>> >> - struct vfio_eeh_pe_op pe_op = { .argsz = sizeof(pe_op), .flags = 0 };
>> >> + struct vfio_eeh_pe_op *pe_op;
>> >> + struct vfio_eeh_pe_err *pe_err;
>> >> +
>> >> + pe_op = malloc(sizeof(*pe_op) + sizeof(*pe_err));
>> >> + pe_err = (void *)pe_op + sizeof(*pe_op);
>> >> + pe_op->argsz = sizeof(*pe_op) + sizeof(*pe_err);
>> >
>> >Surely that argsz can't be correct for most of the operations. The
>> >extended structure should only be there for the error inject ioctl,
>> >yes?
>> >
>>
>> argsz isn't appropriate for most cases because kernel has the check
>> "expected_argsz < passed_argsz", not "expected_argsz ==
>> passed_argsz".
>
>It works for now, but if any of those calls was extended with more
>data, it would break horribly. By setting the argsz greater than
>necessary, you're effectively passing uninitialized data to the
>ioctl(). At the moment, the ioctl() ignores it, but the whole point
>of the argsz value is that in the future, it might not.
>

Thank you for more explanation. I agree that it's worthy to pass precise
argument size. I'll fix it as below in next revision:

>> However, I'll fix it as follows to avoid confusion after collecting
>> more comments:
>>
>> struct vfio_eeh_pe_op *pe_op;
>> struct vfio_eeh_pe_err *pe_err;
>>
>> /* For all cases except error injection */
>> pe_op = malloc(sizeof(*pe_op));
>> pe_op->argsz = sizeof(*pe_op);
>>
>> /* For error injection case here */
>> pe_op = realloc(sizeof(*pe_op) + sizeof(*pe_err));
>> pe_op->argsz = sizeof(*pe_op) + sizeof(*pe_err);
>> pe_err = (void *)pe_op + sizeof(*pe_op);
>>

Thanks,
Gavin

>
>--
>David Gibson | I'll have my music baroque, and my code
>david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
> | _way_ _around_!
>http://www.ozlabs.org/~dgibson