Re: [Xen-devel] [PATCH 2/5] iommu / x86: move call to scan_pci_devices() out of vendor code

From: "Jan Beulich" <JBeulich@suse.com>
To: "Paul Durrant" <paul.durrant@citrix.com>
Cc: Kevin Tian <kevin.tian@intel.com>, Wei Liu <wei.liu2@citrix.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
	xen-devel <xen-devel@lists.xenproject.org>,
	Brian Woods <brian.woods@amd.com>,
	Roger Pau Monne <roger.pau@citrix.com>
Subject: Re: [Xen-devel] [PATCH 2/5] iommu / x86: move call to scan_pci_devices() out of vendor code
Date: Mon, 13 May 2019 09:35:32 -0600	[thread overview]
Message-ID: <5CD98EC4020000780022E421@prv1-mh.provo.novell.com> (raw)
Message-ID: <20190513153532.3Ugg6-9HSMpTGcicE4sm3joxvMcOdRDR_cSMNx-TFdM@z> (raw)
In-Reply-To: <20190508132403.1454-3-paul.durrant@citrix.com>

>>> On 08.05.19 at 15:24, <paul.durrant@citrix.com> wrote:
> It's not vendor specific so it shouldn't really be there.

Perhaps, but this needs better justification:

> --- a/xen/drivers/passthrough/vtd/iommu.c
> +++ b/xen/drivers/passthrough/vtd/iommu.c
> @@ -2372,10 +2372,6 @@ static int __init vtd_setup(void)
>      P(iommu_hap_pt_share, "Shared EPT tables");
>  #undef P
>  
> -    ret = scan_pci_devices();
> -    if ( ret )
> -        goto error;
> -
>      ret = init_vtd_hw();

Even after some looking around, it's not obvious to me that the latter
call doesn't depend on PCI devices being known, more specifically
segment 0's bus2bridge[] having been filled. Nor can I tell whether
there would be some noticeable misbehavior (prior to any guests
starting) if there was a dependency and it got broken by the re-
ordering.

Jan

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