Re: [Xen-devel] [PATCH v2 1/3] x86/physdev: factor out the code to allocate and map a pirq

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.05.17 at 13:52, <roger.pau@xxxxxxxxxx> wrote:
> On Wed, Apr 19, 2017 at 04:11:26PM +0100, Roger Pau Monne wrote:
> [...]
>> +    if ( *pirq_p < 0 )
>> +    {
>> +        if ( pirq )
>> +        {
>> +            dprintk(XENLOG_G_ERR, "dom%d: %d:%d already mapped to %d\n",
>> +                    d->domain_id, *index, *pirq_p, pirq);
>> +            if ( pirq < 0 )
>> +            {
>> +                ret = -EBUSY;
>> +                goto done;
>> +            }
>> +        }
>> +        else if ( msi->entry_nr > 1 && !msi->table_base )
>> +        {
>> +            if ( msi->entry_nr <= 0 || msi->entry_nr > 32 )
>> +                ret = -EDOM;
>> +            else if ( msi->entry_nr != 1 && !iommu_intremap )
>> +                ret = -EOPNOTSUPP;
>> +            else
>> +            {
>> +                while ( msi->entry_nr & (msi->entry_nr - 1) )
>> +                    msi->entry_nr += msi->entry_nr & -msi->entry_nr;
>> +                pirq = get_free_pirqs(d, msi->entry_nr);
>> +                ret = 0;
>> +                if ( pirq < 0 )
>> +                {
>> +                    while ( (msi->entry_nr >>= 1) > 1 )
>> +                        if ( get_free_pirqs(d, msi->entry_nr) > 0 )
>> +                            break;
> 
> Maybe I'm missing something, but I think the code above should be:
> 
>                         if ( (pirq = get_free_pirqs(d, msi->entry_nr)) > 0 )
>                             break;
> 
> Or else the pirq returned by get_free_pirqs is not stored anywhere, and thus
> pirq will be -ENOSPC even when PIRQs have been allocated.
> 
> Let me know if this is true or not, so that I can send a patch to fix the
> current code (which also has this issue).

The code is correct. get_free_pirqs() doesn't alter the slots it
finds free, and here we only want to know how many we could
allocate at this point (given that we weren't able to allocate as
many as were requested).

Jan


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