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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 18.02.14 at 17:56, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> wrote:
> On 02/18/2014 11:41 AM, Jan Beulich wrote:
>>>>> On 18.02.14 at 16:49, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> wrote:
>>> On 02/18/2014 05:16 AM, Jan Beulich wrote:
>>>>>>> On 13.02.14 at 10:48, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:
>>>>>>>> On 12.02.14 at 22:05, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> 
>>>>>>>> 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 mean the old code looks wrong or the new one?

> 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?

We've done with this unfixed quite fine so far, so it's generally
okay to leave as is until 4.4.1 (read: not a regression). I
personally wouldn't mind pushing it in, but only if other similar
not too high priority bug fixes would also go in.

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel