linux-kernel - Re: [PATCH 1/9] iommu/vt-d: Allow interrupts from the entire bus for aliased devices

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Message-ID: <d097d98b-0b8b-5b29-c411-a5dc3949a3e7@deltatee.com>
Date:   Tue, 5 Feb 2019 13:40:36 -0700
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     Joerg Roedel <joro@...tes.org>, Allen Hubbe <allenbh@...il.com>,
        Dave Jiang <dave.jiang@...el.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Serge Semin <fancer.lancer@...il.com>,
        Eric Pilmore <epilmore@...aio.com>,
        iommu@...ts.linux-foundation.org, linux-kselftest@...r.kernel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-ntb@...glegroups.com, David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH 1/9] iommu/vt-d: Allow interrupts from the entire bus for
 aliased devices

On 2019-02-05 12:19 p.m., Jacob Pan wrote:
> On Fri, 1 Feb 2019 10:27:29 -0700
> Logan Gunthorpe <logang@...tatee.com> wrote:
> 
>> On 2019-02-01 9:44 a.m., Joerg Roedel wrote:
>>> On Thu, Jan 31, 2019 at 11:56:48AM -0700, Logan Gunthorpe wrote:  
>>>> @@ -394,6 +402,10 @@ static int set_msi_sid(struct irte *irte,
>>>> struct pci_dev *dev) set_irte_sid(irte, SVT_VERIFY_BUS, SQ_ALL_16,
>>>>  			     PCI_DEVID(PCI_BUS_NUM(data.alias),
>>>>  				       dev->bus->number));
> I guess devfn can be removed also. but that is separate cleanup.

Actually, no, I've dug into this and we *do* need the devfn here but
it's needlessly confusing. We should not be using PCI_DEVID() as we
aren't actually representing a DEVID in this case...

According to the Intel VT-D spec, when using SVT_VERIFY_BUS, the MSB of
the SID field represents the starting bus number and the LSB represents
the end bus number. The requester id's bus number must then be within
that range. The PCI_DEVID macro matches these semantics if you assume
the devfn is the end bus, but doesn't really make sense here and just
confuses the issue.

So the code was correct, I'll just try to clean it up to make it less
confusing.

Thanks,

Logan