linux-kernel - RE: [patch 21/32] NTB/msi: Convert to msi_on_each

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Date:   Sun, 12 Dec 2021 01:56:31 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Jason Gunthorpe <jgg@...dia.com>
CC:     "Jiang, Dave" <dave.jiang@...el.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Marc Zygnier <maz@...nel.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        "Dey, Megha" <megha.dey@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jon Mason <jdmason@...zu.us>, Allen Hubbe <allenbh@...il.com>,
        "linux-ntb@...glegroups.com" <linux-ntb@...glegroups.com>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        "x86@...nel.org" <x86@...nel.org>, "Rodel, Jorg" <jroedel@...e.de>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>
Subject: RE: [patch 21/32] NTB/msi: Convert to msi_on_each_desc()

> From: Thomas Gleixner <tglx@...utronix.de>
> Sent: Saturday, December 11, 2021 9:05 PM
> 
> Kevin,
> 
> On Sat, Dec 11 2021 at 07:44, Kevin Tian wrote:
> >> From: Thomas Gleixner <tglx@...utronix.de>
> >> On Fri, Dec 10 2021 at 08:39, Jason Gunthorpe wrote:
> >> > It is clever, we don't have an vIOMMU that supplies vIR today, so by
> >> > definition all guests are excluded and only bare metal works.
> >>
> >> Dammit. Now you spilled the beans. :)
> >
> > Unfortunately we do have that today. Qemu supports IR for
> > both AMD and Intel vIOMMU.
> 
> can you point me to the code?
> 
> All I can find is drivers/iommu/virtio-iommu.c but I can't find anything
> vIR related there.
> 

Well, virtio-iommu is a para-virtualized vIOMMU implementations.

In reality there are also fully emulated vIOMMU implementations (e.g.
Qemu fully emulates Intel/AMD/ARM IOMMUs). In those configurations
the IR logic in existing iommu drivers just apply:

	drivers/iommu/intel/irq_remapping.c
	drivers/iommu/amd/iommu.c
	...

As I replied in another mail, the 1st vIR implementation was introduced
to Qemu back to 2016:

commit 1121e0afdcfa0cd40e36bd3acff56a3fac4f70fd
Author: Peter Xu <peterx@...hat.com>
Date:   Thu Jul 14 13:56:13 2016 +0800

    x86-iommu: introduce "intremap" property

    Adding one property for intel-iommu devices to specify whether we should
    support interrupt remapping. By default, IR is disabled. To enable it,
    we should use (take Intel IOMMU as example):

      -device intel_iommu,intremap=on

    This property can be shared by Intel and future AMD IOMMUs.

    Signed-off-by: Peter Xu <peterx@...hat.com>
    Reviewed-by: Michael S. Tsirkin <mst@...hat.com>
    Signed-off-by: Michael S. Tsirkin <mst@...hat.com>

Thanks
Kevin