Re: [Xen-devel] [PATCH v2 08/30] xen/x86: do the PCI scan unconditionally

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

On Thu, Sep 29, 2016 at 07:55:00AM -0600, Jan Beulich wrote:
> >>> On 27.09.16 at 17:57, <roger.pau@xxxxxxxxxx> wrote:
> > Instead of being tied to the presence of an IOMMU
> 
> At the very least I'd expect the "why" aspect to get mentioned
> here.

TBH, it seems simpler to have it there rather than conditional to the 
presence of an IOMMU. Also, I think scan_pci_devices failing should be 
fatal. Would you be OK with me adding a panic if the scan fails?

> > --- 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;
> >  }
> 
> Not how an error return from the function at least here does not
> get ignored, leading to the IOMMU not getting enabled. This behavior
> should be preserved, and I think it actually should extend to VT-d.
> Furthermore iiuc you make PVHv2 Dom0 setup depend on this
> succeeding, which may then require further propagation of the
> success status here (or maybe, just like PVHv1, you require a
> functional IOMMU, in which case failing IOMMU setup would be
> sufficient).

Yes, PVHv2, just like PVHv1 requires a functional IOMMU, see 
check_hwdom_reqs in passthrough/iommu.c (if the hardware domain is using a 
translated paging mode an IOMMU is required).

Roger.

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