Re: Write to srvio_numvfs triggers kernel panic

[Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>]

Hello Bjorn,

Bjorn Helgaas <helgaas@kernel.org> writes:

> On Mon, May 09, 2022 at 11:39:30PM -0700, Christoph Hellwig wrote:
>> On Mon, May 09, 2022 at 10:58:57AM -0600, Alex Williamson wrote:
>> > is_physfn = 0, is_virtfn = 0: A non-SR-IOV function
>> > is_physfn = 1, is_virtfn = 0: An SR-IOV PF
>> > is_physfn = 0, is_virtfn = 1: An SR-IOV VF
>> > 
>> > As implemented with bit fields this is 2 bits, which is more space
>> > efficient than an enum.  Thanks,
>> 
>> A two-bit bitfield with explicit constants for the values would probably
>> still much eaiser to understand.
>> 
>> And there is some code that seems to intepret is_physfn a bit odd, e.g.:
>> 
>> arch/powerpc/kernel/eeh_sysfs.c:        np = pci_device_to_OF_node(pdev->is_physfn ? pdev : pdev->physfn);
>> arch/powerpc/kernel/eeh_sysfs.c:        np = pci_device_to_OF_node(pdev->is_physfn ? pdev : pdev->physfn);
>
> "dev->sriov != NULL" and "dev->is_physfn" are basically the same and
> many of the dev->is_physfn uses in drivers/pci would end up being
> simpler if replaced with dev->sriov, e.g.,
>
>   int pci_iov_virtfn_bus(struct pci_dev *dev, int vf_id)
>   {
>     if (!dev->is_physfn)
>       return -EINVAL;
>     return dev->bus->number + ((dev->devfn + dev->sriov->offset +
> 				dev->sriov->stride * vf_id) >> 8);
>   }
>
> would be more obvious as:
>
>   if (dev->sriov)
>     return dev->bus->number + ((dev->devfn + dev->sriov->offset +
> 				dev->sriov->stride * vf_id) >> 8);
>   return -EINVAL;

I'm not sure that this will work because dev->sriov and dev->physfn are
stored in the same union. 


-- 
Volodymyr Babchuk at EPAM