Re: [Xen-devel] [PATCH v2 01/11] vt-d: fix the IOMMU flush issue

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 26.04.16 at 12:15, <quan.xu@xxxxxxxxx> wrote:
> On April 26, 2016 5:11 PM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>> >>> On 26.04.16 at 04:18, <quan.xu@xxxxxxxxx> wrote:
>> > On April 25, 2016 5:22 PM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>> >> >>> On 18.04.16 at 16:00, <quan.xu@xxxxxxxxx> wrote:
>> >> > --- a/xen/drivers/passthrough/vtd/iommu.c
>> >> > +++ b/xen/drivers/passthrough/vtd/iommu.c
>> >> > @@ -558,14 +558,16 @@ static void iommu_flush_all(void)
>> >> >      }
>> >> >  }
>> >> >
>> >> > -static void __intel_iommu_iotlb_flush(struct domain *d, unsigned long
>> gfn,
>> >> > -        int dma_old_pte_present, unsigned int page_count)
>> >> > +static int iommu_flush_iotlb(struct domain *d, unsigned long gfn,
>> >> > +                             int dma_old_pte_present,
>> >> > +                             unsigned int page_count)
>> >> >  {
>> >> >      struct hvm_iommu *hd = domain_hvm_iommu(d);
>> >> >      struct acpi_drhd_unit *drhd;
>> >> >      struct iommu *iommu;
>> >> >      int flush_dev_iotlb;
>> >> >      int iommu_domid;
>> >> > +    int rc = 0;
>> >>
>> >> Pointless initializer.
>> >
>> > I am afraid not.
>> > In case I don't initialize 'rc', the compiler prints out  " error:
>> > 'rc' may be used uninitialized in this function 
> [-Werror=maybe-uninitialized]".
>> 
>> Looking at the patch again I can't see why that would be the case.
>> Are you certain this isn't a result of subsequent patches, IOW did you try 
> this
>> with just this one patch applied? 
> 
> Yes, I test it with this only patch again.
> 
> The same result.
> 
>> rc gets initialized in both the if() and the else
>> branches, and there's no label allowing that initialization to be 
> bypassed...
> 
> look at this function again, 
> 
>>> func
> iommu_flush_iotlb()
> {
>     int rc;
> 
>     for_each_drhd_unit ( drhd )
>     {
>         if ()
>             rc ..
>         else
>             rc ..
>     }
> 
>     return rc;
> }

Ah, I'm sorry - the patch context didn't make it obvious this is in
a loop.

Jan


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