From: Stefan Hajnoczi <stefanha@redhat.com>
To: Jag Raman <jag.raman@oracle.com>
Cc: "Elena Ufimtseva" <elena.ufimtseva@oracle.com>,
"John Johnson" <john.g.johnson@oracle.com>,
"thuth@redhat.com" <thuth@redhat.com>,
"bleal@redhat.com" <bleal@redhat.com>,
"swapnil.ingle@nutanix.com" <swapnil.ingle@nutanix.com>,
"john.levon@nutanix.com" <john.levon@nutanix.com>,
"Philippe Mathieu-Daudé" <philmd@redhat.com>,
qemu-devel <qemu-devel@nongnu.org>,
"wainersm@redhat.com" <wainersm@redhat.com>,
"Alex Williamson" <alex.williamson@redhat.com>,
"thanos.makatos@nutanix.com" <thanos.makatos@nutanix.com>,
"Marc-André Lureau" <marcandre.lureau@gmail.com>,
"crosa@redhat.com" <crosa@redhat.com>,
"pbonzini@redhat.com" <pbonzini@redhat.com>,
"alex.bennee@linaro.org" <alex.bennee@linaro.org>
Subject: Re: [PATCH v4 11/14] vfio-user: IOMMU support for remote device
Date: Thu, 6 Jan 2022 13:10:51 +0000 [thread overview]
Message-ID: <YdbqW465lBlM//FD@stefanha-x1.localdomain> (raw)
In-Reply-To: <D9E0A4CC-83E9-460F-BBB9-D5DABBA9ED19@oracle.com>
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On Tue, Dec 21, 2021 at 04:32:05AM +0000, Jag Raman wrote:
> > On Dec 20, 2021, at 9:36 AM, Stefan Hajnoczi <stefanha@redhat.com> wrote:
> > On Fri, Dec 17, 2021 at 08:00:35PM +0000, Jag Raman wrote:
> >>> On Dec 16, 2021, at 9:40 AM, Stefan Hajnoczi <stefanha@redhat.com> wrote:
> >>> On Wed, Dec 15, 2021 at 10:35:35AM -0500, Jagannathan Raman wrote:
> >>> Also, why is PCI Memory Space isolated via VFUIOMMU but PCI IO Space is
> >>> not?
> >>
> >> If I understand correctly, the IO address space translates sysmem address to
> >> direct device access (such as I2C). Once we are inside a device, we already
> >> have access to all parts of the device (unlike RAM which sits outside the device).
> >> So didn’t think device would go via IOMMU to access IO. Also didn’t see any
> >> other IOMMU translating IO address space accesses.
> >
> > I reviewed how BARs are configured with VFIO:
> >
> > 1. When the guest writes to the vfio-pci PCIDevice's Configuration Space
> > the write is forwarded to the VFIO device (i.e. vfio-user or VFIO
> > kernel ioctl).
> >
> > 2. The vfio-user server receives the Configuration Space write and
> > forwards it to pci_dev (the PCIDevice we're serving up). BAR mappings
> > are updated in the vfio-user server so the BAR MemoryRegions are
> > mapped/unmapped at the locations given by the guest.
> >
> > This applies for both Memory and IO Space accesses.
> >
> > Because this patch series does not isolate IO Space between VfuObject
> > instances the MemoryRegions will collide when two guests map IO Space
> > BARs of different devices at the same IO Space address. In other words,
> > vfu_object_bar_rw() uses the global address_space_io and that means
> > collisions can occur.
>
> I agree that collision could occur from the CPU end. But I'm not if IOMMU
> needs to translate IO space.
QEMU's IOMMUs do not translate IO Space addresses AFAIK.
IO Space just needs to be isolated between vfio-user server instances so
there is no collision when one client maps an IO Space BAR to the same
address as another client.
I think the cleanest way of achieving that is by creating a
per-vfio-user server PCI bus with an address_space_io MemoryRegion.
Stefan
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next prev parent reply other threads:[~2022-01-06 13:13 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-15 15:35 [PATCH v4 00/14] vfio-user server in QEMU Jagannathan Raman
2021-12-15 15:35 ` [PATCH v4 01/14] configure, meson: override C compiler for cmake Jagannathan Raman
2021-12-15 15:35 ` [PATCH v4 02/14] tests/avocado: Specify target VM argument to helper routines Jagannathan Raman
2021-12-15 15:54 ` Philippe Mathieu-Daudé
2021-12-15 22:04 ` Beraldo Leal
2021-12-16 21:28 ` Jag Raman
2021-12-15 15:35 ` [PATCH v4 03/14] vfio-user: build library Jagannathan Raman
2021-12-15 15:35 ` [PATCH v4 04/14] vfio-user: define vfio-user-server object Jagannathan Raman
2021-12-16 9:33 ` Stefan Hajnoczi
2021-12-17 2:17 ` Jag Raman
2021-12-16 9:58 ` Stefan Hajnoczi
2021-12-17 2:31 ` Jag Raman
2021-12-17 8:28 ` Stefan Hajnoczi
2021-12-15 15:35 ` [PATCH v4 05/14] vfio-user: instantiate vfio-user context Jagannathan Raman
2021-12-16 9:55 ` Stefan Hajnoczi
2021-12-16 21:32 ` Jag Raman
2021-12-15 15:35 ` [PATCH v4 06/14] vfio-user: find and init PCI device Jagannathan Raman
2021-12-16 10:39 ` Stefan Hajnoczi
2021-12-17 3:12 ` Jag Raman
2021-12-15 15:35 ` [PATCH v4 07/14] vfio-user: run vfio-user context Jagannathan Raman
2021-12-16 11:17 ` Stefan Hajnoczi
2021-12-17 17:59 ` Jag Raman
2021-12-20 8:29 ` Stefan Hajnoczi
2021-12-21 3:04 ` Jag Raman
2022-01-05 10:38 ` Thanos Makatos
2022-01-06 13:35 ` Stefan Hajnoczi
2022-01-10 17:56 ` John Levon
2022-01-11 9:36 ` Stefan Hajnoczi
2022-01-11 13:12 ` Jag Raman
2021-12-15 15:35 ` [PATCH v4 08/14] vfio-user: handle PCI config space accesses Jagannathan Raman
2021-12-16 11:30 ` Stefan Hajnoczi
2021-12-16 11:47 ` John Levon
2021-12-16 16:00 ` Stefan Hajnoczi
2021-12-15 15:35 ` [PATCH v4 09/14] vfio-user: handle DMA mappings Jagannathan Raman
2021-12-16 13:24 ` Stefan Hajnoczi
2021-12-17 19:11 ` Jag Raman
2021-12-15 15:35 ` [PATCH v4 10/14] vfio-user: handle PCI BAR accesses Jagannathan Raman
2021-12-16 14:10 ` Stefan Hajnoczi
2021-12-17 19:12 ` Jag Raman
2021-12-15 15:35 ` [PATCH v4 11/14] vfio-user: IOMMU support for remote device Jagannathan Raman
2021-12-16 14:40 ` Stefan Hajnoczi
2021-12-17 20:00 ` Jag Raman
2021-12-20 14:36 ` Stefan Hajnoczi
2021-12-21 4:32 ` Jag Raman
2022-01-06 13:10 ` Stefan Hajnoczi [this message]
2021-12-15 15:35 ` [PATCH v4 12/14] vfio-user: handle device interrupts Jagannathan Raman
2021-12-16 15:56 ` Stefan Hajnoczi
2021-12-15 15:35 ` [PATCH v4 13/14] vfio-user: register handlers to facilitate migration Jagannathan Raman
2021-12-15 15:35 ` [PATCH v4 14/14] vfio-user: avocado tests for vfio-user Jagannathan Raman
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