Re: [PATCH 2/2] x86/pci: Remove unnecessary check in VF value computation

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

On 02/18/2014 11:41 AM, Jan Beulich wrote:
>>>> On 18.02.14 at 16:49, Boris Ostrovsky <boris.ostrovsky@oracle.com> wrote:
>> On 02/18/2014 05:16 AM, Jan Beulich wrote:
>>>>>> On 13.02.14 at 10:48, "Jan Beulich" <JBeulich@suse.com> wrote:
>>>>>>> On 12.02.14 at 22:05, Boris Ostrovsky <boris.ostrovsky@oracle.com> wrote:
>>>>> This test is already performed a couple of lines above.
>>>> Except that it's the wrong code you remove:
>>> No opinion on this alternative at all?
>> Sorry Jan, I didn't realize you were waiting for me on this.
>>
>> Yes, your version is fine although to be honest I don't see how the
>> original patch had any issues with division by zero since we'd still be
>> inside the 'if (stride)' clause.
> It's the very division that this patch removes:
>
>>>> --- a/xen/arch/x86/msi.c
>>>> +++ b/xen/arch/x86/msi.c
>>>> @@ -635,7 +635,7 @@ static u64 read_pci_mem_bar(u16 seg, u8
>>>>                return 0;
>>>>            base = pos + PCI_SRIOV_BAR;
>>>>            vf -= PCI_BDF(bus, slot, func) + offset;
>>>> -        if ( vf < 0 || (vf && vf % stride) )
>>>> +        if ( vf < 0 )
>>>>                return 0;
>>>>            if ( stride )
>>>>            {
> Which isn't inside the if(stride).


Yes, I see it now. I was staring at a wrong line.

This actually now looks like a bug. You do check above for '(num_vf > 1 
&& !stride) ' but presumably if things are really messed up num_vf can 
be 1 but vf is 0. And then if stride is zero too then we are not doing 
particularly well.

So probably this should go into 4.4 as well?

-boris