Re: [Xen-devel] [PATCH v3.1 07/15] xen/x86: do the PCI scan unconditionally

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

On Mon, Oct 31, 2016 at 10:47:15AM -0600, Jan Beulich wrote:
> >>> On 29.10.16 at 10:59, <roger.pau@xxxxxxxxxx> wrote:
> > --- a/xen/arch/x86/setup.c
> > +++ b/xen/arch/x86/setup.c
> > @@ -1491,6 +1491,8 @@ void __init noreturn __start_xen(unsigned long mbi_p)
> >  
> >      early_msi_init();
> >  
> > +    scan_pci_devices();
> > +
> >      iommu_setup();    /* setup iommu if available */
> >  
> >      smp_prepare_cpus(max_cpus);
> > --- a/xen/drivers/passthrough/amd/pci_amd_iommu.c
> > +++ b/xen/drivers/passthrough/amd/pci_amd_iommu.c
> > @@ -219,7 +219,8 @@ int __init amd_iov_detect(void)
> >  
> >      if ( !amd_iommu_perdev_intremap )
> >          printk(XENLOG_WARNING "AMD-Vi: Using global interrupt remap table 
> > is not recommended (see XSA-36)!\n");
> > -    return scan_pci_devices();
> > +
> > +    return 0;
> >  }
> 
> I'm relatively certain that I did point out on a prior version that the
> error handling here gets lost. At the very least the commit message
> should provide a reason for doing so; even better would be if there
> was no behavioral change (other than the point in time where this
> happens slightly changing).

Behaviour here is different on Intel or AMD hardware, on Intel failure to 
scan the PCI bus will not be fatal, and the IOMMU will be enabled anyway. On 
AMD OTOH failure to scan the PCI bus will cause the IOMMU to be disabled. 
I expect we should be able to behave equally for both Intel and AMD, so 
which one should be used?

Roger.

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