Re: [PATCH v2 1/3] PCI: simplify (and thus correct) pci_get_pdev{,_by_domain}()

[Jan Beulich <jbeulich@xxxxxxxx>]

On 11.08.2022 15:11, Andrew Cooper wrote:
> On 11/08/2022 11:51, Jan Beulich wrote:
>> The last "wildcard" use of either function went away with f591755823a7
>> ("IOMMU/PCI: don't let domain cleanup continue when device de-assignment
>> failed"). Don't allow them to be called this way anymore. Besides
>> simplifying the code this also fixes two bugs:
>>
>> 1) When seg != -1, the outer loops should have been terminated after the
>>    first iteration, or else a device with the same BDF but on another
>>    segment could be found / returned.
>>
>> Reported-by: Rahul Singh <rahul.singh@xxxxxxx>
>>
>> 2) When seg == -1 calling get_pseg() is bogus. The function (taking a
>>    u16) would look for segment 0xffff, which might exist. If it exists,
>>    we might then find / return a wrong device.
>>
>> In pci_get_pdev_by_domain() also switch from using the per-segment list
>> to using the per-domain one, with the exception of the hardware domain
>> (see the code comment there).
>>
>> While there also constify "pseg" and drop "pdev"'s already previously
>> unnecessary initializer.
>>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Thanks.

> I'm not totally convinced that special casing hwdom is right, because
> quarantine devices are domio not hwdom.  But I also can't identify a
> case where it's definitely wrong either.
> 
>> --- a/xen/include/xen/pci.h
>> +++ b/xen/include/xen/pci.h
>> @@ -177,10 +177,10 @@ int pci_add_device(u16 seg, u8 bus, u8 d
>>  int pci_remove_device(u16 seg, u8 bus, u8 devfn);
>>  int pci_ro_device(int seg, int bus, int devfn);
>>  int pci_hide_device(unsigned int seg, unsigned int bus, unsigned int devfn);
>> -struct pci_dev *pci_get_pdev(int seg, int bus, int devfn);
>> +struct pci_dev *pci_get_pdev(uint16_t seg, uint8_t bus, uint8_t devfn);
> 
> I was going to make a request, but I can't quite get it to compile...
> 
> Passing sbdf as 3 parameters is a waste, and it would be great if we
> could take this opportunity to improve.
> 
> Sadly,
> 
> -struct pci_dev *pci_get_pdev(uint16_t seg, uint8_t bus, uint8_t devfn);
> +struct pci_dev *pci_get_pdev(pci_sbdf_t sbdf);
> +
> +#define pci_get_pdev(...)                               \
> +    ({                                                  \
> +        count_args(__VA_ARGS__) == 1                    \
> +            ? pci_get_pdev(__VA_ARGS__)                 \
> +            : pci_get_pdev(PCI_SBDF(__VA_ARGS__));      \
> +    })
> 
> this doesn't quite compile as a transition plan, and I'm stuck for
> further ideas.

Just look at patch 2.

Jan