linux-kernel - Re: [patch V2 24/46] PCI: vmd: Mark VMD irqdomain with DOMAIN_BUS_VMD

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Date:   Wed, 30 Sep 2020 09:57:33 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Derrick, Jonathan" <jonathan.derrick@...el.com>
CC:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "sivanich@....com" <sivanich@....com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        "haiyangz@...rosoft.com" <haiyangz@...rosoft.com>,
        "Dey, Megha" <megha.dey@...el.com>,
        "Lu, Baolu" <baolu.lu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "jgross@...e.com" <jgross@...e.com>,
        "kys@...rosoft.com" <kys@...rosoft.com>,
        "sstabellini@...nel.org" <sstabellini@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
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        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "maz@...nel.org" <maz@...nel.org>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
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        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>
Subject: Re: [patch V2 24/46] PCI: vmd: Mark VMD irqdomain with
 DOMAIN_BUS_VMD_MSI

On Wed, Sep 30, 2020 at 12:45:30PM +0000, Derrick, Jonathan wrote:
> Hi Jason
> 
> On Mon, 2020-08-31 at 11:39 -0300, Jason Gunthorpe wrote:
> > On Wed, Aug 26, 2020 at 01:16:52PM +0200, Thomas Gleixner wrote:
> > > From: Thomas Gleixner <tglx@...utronix.de>
> > > 
> > > Devices on the VMD bus use their own MSI irq domain, but it is not
> > > distinguishable from regular PCI/MSI irq domains. This is required
> > > to exclude VMD devices from getting the irq domain pointer set by
> > > interrupt remapping.
> > > 
> > > Override the default bus token.
> > > 
> > > Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> > > Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>
> > >  drivers/pci/controller/vmd.c |    6 ++++++
> > >  1 file changed, 6 insertions(+)
> > > 
> > > +++ b/drivers/pci/controller/vmd.c
> > > @@ -579,6 +579,12 @@ static int vmd_enable_domain(struct vmd_
> > >  		return -ENODEV;
> > >  	}
> > >  
> > > +	/*
> > > +	 * Override the irq domain bus token so the domain can be distinguished
> > > +	 * from a regular PCI/MSI domain.
> > > +	 */
> > > +	irq_domain_update_bus_token(vmd->irq_domain, DOMAIN_BUS_VMD_MSI);
> > > +
> > 
> > Having the non-transparent-bridge hold a MSI table and
> > multiplex/de-multiplex IRQs looks like another good use case for
> > something close to pci_subdevice_msi_create_irq_domain()?
> > 
> > If each device could have its own internal MSI-X table programmed
> > properly things would work alot better. Disable capture/remap of the
> > MSI range in the NTB.

> We can disable the capture and remap in newer devices so we don't even
> need the irq domain.

You'd still need an irq domain, it just comes from
pci_subdevice_msi_create_irq_domain() instead of internal to this
driver.

> I would however like to determine if the MSI data bits could be used
> for individual devices to have the IRQ domain subsystem demultiplex the
> virq from that and eliminate the IRQ list iteration.

Yes, exactly. This new pci_subdevice_msi_create_irq_domain() creates
*proper* fully functional interrupts, no need for any IRQ handler in
this driver.

> A concern I have about that scheme is virtualization as I think those
> bits are used to route to the virtual vector.

It should be fine with this patch series, consult with Megha how
virtualization is working with IDXD/etc

Jason