From: Jason Gunthorpe via iommu <iommu@lists.linux-foundation.org>
To: "Mika Penttilä" <mika.penttila@nextfour.com>
Cc: Allen Hubbe <allenbh@gmail.com>,
"linux-s390@vger.kernel.org" <linux-s390@vger.kernel.org>,
"Tian, Kevin" <kevin.tian@intel.com>,
"x86@kernel.org" <x86@kernel.org>,
"Jiang, Dave" <dave.jiang@intel.com>,
"Raj, Ashok" <ashok.raj@intel.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Marc Zygnier <maz@kernel.org>, Heiko Carstens <hca@linux.ibm.com>,
LKML <linux-kernel@vger.kernel.org>,
"iommu@lists.linux-foundation.org"
<iommu@lists.linux-foundation.org>,
Christian Borntraeger <borntraeger@de.ibm.com>,
Alex Williamson <alex.williamson@redhat.com>,
Joerg Roedel <jroedel@suse.de>,
Bjorn Helgaas <helgaas@kernel.org>,
"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
"linux-ntb@googlegroups.com" <linux-ntb@googlegroups.com>,
Thomas Gleixner <tglx@linutronix.de>,
Logan Gunthorpe <logang@deltatee.com>,
"Dey, Megha" <megha.dey@intel.com>
Subject: Re: [patch 21/32] NTB/msi: Convert to msi_on_each_desc()
Date: Sun, 12 Dec 2021 19:27:58 -0400 [thread overview]
Message-ID: <20211212232758.GL6385@nvidia.com> (raw)
In-Reply-To: <3f6d4bd7-8b60-1976-73a4-f5ef7f3dbf27@nextfour.com>
On Sun, Dec 12, 2021 at 08:44:46AM +0200, Mika Penttilä wrote:
> > /*
> > * The MSIX mappable capability informs that MSIX data of a BAR can be mmapped
> > * which allows direct access to non-MSIX registers which happened to be within
> > * the same system page.
> > *
> > * Even though the userspace gets direct access to the MSIX data, the existing
> > * VFIO_DEVICE_SET_IRQS interface must still be used for MSIX configuration.
> > */
> > #define VFIO_REGION_INFO_CAP_MSIX_MAPPABLE 3
> >
> > IIRC this was introduced for PPC when a device has MSI-X in the same BAR as
> > other MMIO registers. Trapping MSI-X leads to performance downgrade on
> > accesses to adjacent registers. MSI-X can be mapped by userspace because
> > PPC already uses a hypercall mechanism for interrupt. Though unclear about
> > the detail it sounds a similar usage as proposed here.
> >
> > Thanks
> > Kevin
>
> I see VFIO_REGION_INFO_CAP_MSIX_MAPPABLE is always set so if msix table is
> in its own bar, qemu never traps/emulates the access.
It is some backwards compat, the kernel always sets it to indicate a
new kernel, that doesn't mean qemu doesn't trap.
As the comment says, ""VFIO_DEVICE_SET_IRQS interface must still be
used for MSIX configuration"" so there is no way qemu can meet that
without either trapping the MSI page or using a special hypercall
(ppc)
Jason
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prev parent reply other threads:[~2021-12-12 23:28 UTC|newest]
Thread overview: 71+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20211126230957.239391799@linutronix.de>
[not found] ` <20211126232735.547996838@linutronix.de>
[not found] ` <7daba0e2-73a3-4980-c3a5-a71f6b597b22@deltatee.com>
[not found] ` <874k7ueldt.ffs@tglx>
[not found] ` <6ba084d6-2b26-7c86-4526-8fcd3d921dfd@deltatee.com>
[not found] ` <87ilwacwp8.ffs@tglx>
[not found] ` <d6f13729-1b83-fa7d-3f0d-98d4e3f7a2aa@deltatee.com>
[not found] ` <87v909bf2k.ffs@tglx>
[not found] ` <20211130202800.GE4670@nvidia.com>
[not found] ` <87o861banv.ffs@tglx>
[not found] ` <20211201001748.GF4670@nvidia.com>
2021-12-01 10:16 ` [patch 21/32] NTB/msi: Convert to msi_on_each_desc() Thomas Gleixner
2021-12-01 13:00 ` Jason Gunthorpe via iommu
2021-12-01 17:35 ` Thomas Gleixner
2021-12-01 18:14 ` Jason Gunthorpe via iommu
2021-12-01 18:46 ` Logan Gunthorpe
2021-12-01 20:21 ` Thomas Gleixner
2021-12-02 0:01 ` Thomas Gleixner
2021-12-02 13:55 ` Jason Gunthorpe via iommu
2021-12-02 14:23 ` Greg Kroah-Hartman
2021-12-02 14:45 ` Jason Gunthorpe via iommu
2021-12-02 19:25 ` Thomas Gleixner
2021-12-02 20:00 ` Jason Gunthorpe via iommu
2021-12-02 22:31 ` Thomas Gleixner
2021-12-03 0:37 ` Jason Gunthorpe via iommu
2021-12-03 15:07 ` Thomas Gleixner
2021-12-03 16:41 ` Jason Gunthorpe via iommu
2021-12-04 14:20 ` Thomas Gleixner
2021-12-05 14:16 ` Thomas Gleixner
2021-12-06 14:43 ` Jason Gunthorpe via iommu
2021-12-06 15:47 ` Thomas Gleixner
2021-12-06 17:00 ` Jason Gunthorpe via iommu
2021-12-06 20:28 ` Thomas Gleixner
2021-12-06 21:06 ` Jason Gunthorpe via iommu
2021-12-06 22:21 ` Thomas Gleixner
2021-12-06 14:19 ` Jason Gunthorpe via iommu
2021-12-06 15:06 ` Thomas Gleixner
2021-12-09 6:26 ` Tian, Kevin
2021-12-09 9:03 ` Thomas Gleixner
2021-12-09 12:17 ` Tian, Kevin
2021-12-09 15:57 ` Thomas Gleixner
2021-12-10 7:37 ` Tian, Kevin
2021-12-09 5:41 ` Tian, Kevin
2021-12-09 5:47 ` Jason Wang
2021-12-01 16:28 ` Dave Jiang
2021-12-01 18:41 ` Thomas Gleixner
2021-12-01 18:47 ` Dave Jiang
2021-12-01 20:25 ` Thomas Gleixner
2021-12-01 21:21 ` Dave Jiang
2021-12-01 21:44 ` Thomas Gleixner
2021-12-01 21:49 ` Dave Jiang
2021-12-01 22:03 ` Thomas Gleixner
2021-12-01 22:53 ` Dave Jiang
2021-12-01 23:57 ` Thomas Gleixner
2021-12-09 5:23 ` Tian, Kevin
2021-12-09 8:37 ` Thomas Gleixner
2021-12-09 12:31 ` Tian, Kevin
2021-12-09 16:21 ` Jason Gunthorpe via iommu
2021-12-09 20:32 ` Thomas Gleixner
2021-12-09 20:58 ` Jason Gunthorpe via iommu
2021-12-09 22:09 ` Thomas Gleixner
2021-12-10 0:26 ` Thomas Gleixner
2021-12-10 7:29 ` Tian, Kevin
2021-12-10 12:13 ` Thomas Gleixner
2021-12-11 8:06 ` Tian, Kevin
2021-12-10 12:39 ` Jason Gunthorpe via iommu
2021-12-10 19:00 ` Thomas Gleixner
2021-12-11 7:44 ` Tian, Kevin
2021-12-11 13:04 ` Thomas Gleixner
2021-12-12 1:56 ` Tian, Kevin
2021-12-12 20:55 ` Thomas Gleixner
2021-12-12 23:37 ` Jason Gunthorpe via iommu
2021-12-13 7:50 ` Tian, Kevin
2021-12-11 7:52 ` Tian, Kevin
2021-12-12 0:12 ` Thomas Gleixner
2021-12-12 2:14 ` Tian, Kevin
2021-12-12 20:50 ` Thomas Gleixner
2021-12-12 23:42 ` Jason Gunthorpe via iommu
2021-12-10 7:36 ` Tian, Kevin
2021-12-10 12:30 ` Jason Gunthorpe via iommu
2021-12-12 6:44 ` Mika Penttilä
2021-12-12 23:27 ` Jason Gunthorpe via iommu [this message]
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