From: Alex Williamson <alex.williamson@redhat.com>
To: Eric Auger <eric.auger@linaro.org>
Cc: eric.auger@st.com, robin.murphy@arm.com, will.deacon@arm.com,
joro@8bytes.org, tglx@linutronix.de, jason@lakedaemon.net,
marc.zyngier@arm.com, christoffer.dall@linaro.org,
linux-arm-kernel@lists.infradead.org, patches@linaro.org,
linux-kernel@vger.kernel.org, Bharat.Bhushan@freescale.com,
pranav.sawargaonkar@gmail.com, p.fedin@samsung.com,
iommu@lists.linux-foundation.org, Jean-Philippe.Brucker@arm.com,
julien.grall@arm.com, yehuday@marvell.com
Subject: Re: [PATCH v9 7/7] vfio/type1: return MSI geometry through VFIO_IOMMU_GET_INFO capability chains
Date: Mon, 9 May 2016 17:03:12 -0600 [thread overview]
Message-ID: <20160509170312.06e9c4fe@t450s.home> (raw)
In-Reply-To: <5729E5BB.1030101@linaro.org>
On Wed, 4 May 2016 14:06:19 +0200
Eric Auger <eric.auger@linaro.org> wrote:
> Hi Alex,
> On 05/04/2016 01:54 PM, Eric Auger wrote:
> > This patch allows the user-space to retrieve the MSI geometry. The
> > implementation is based on capability chains, now also added to
> > VFIO_IOMMU_GET_INFO.
>
> If you prefer we could consider this patch outside of the main series
> since it brings extra functionalities (MSI geometry reporting). In a
> first QEMU integration we would live without knowing the MSI geometry I
> think, all the more so I currently report an arbitrary number of
> requested IOVA pages. The computation of the exact number of doorbells
> to map brings extra complexity and I did not address this issue yet.
>
> It sketches a possible user API to report the MSI geometry based on the
> capability chains, as you suggested some time ago. I am currently busy
> drafting a QEMU integration.
How would the user know that reserved MSI mappings are requires or
available without this? Wouldn't the only option be for userspace to
try to map something with the reserved MSI flag set and see if the
kernel accepts it? That's not a very desirable programming model. The
arbitrary size is pretty ugly, but it at least makes for a consistent
user interface. Is it a functional issue if we overestimate the size
or is it just a matter of wasting IOVA space? Is there significant
harm in making it obscenely large, like 1MB? The reference counting and
re-use of IOVA pages seems like we may often only be using a single
IOVA page for multiple doorbells. I guess I'm leaning towards defining
the API even if the value is somewhat arbitrary because we'd rather have
control of this rather than having the user guess and try to rope them
back in later to use a kernel recommended value. Thanks,
Alex
next prev parent reply other threads:[~2016-05-09 23:03 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-04 11:54 [PATCH v9 0/7] KVM PCIe/MSI passthrough on ARM/ARM64: kernel part 3/3: vfio changes Eric Auger
2016-05-04 11:54 ` [PATCH v9 1/7] vfio: introduce a vfio_dma type field Eric Auger
2016-05-04 11:54 ` [PATCH v9 2/7] vfio/type1: vfio_find_dma accepting a type argument Eric Auger
2016-05-09 22:49 ` Alex Williamson
2016-05-10 14:54 ` Eric Auger
2016-05-04 11:54 ` [PATCH v9 3/7] vfio/type1: bypass unmap/unpin and replay for VFIO_IOVA_RESERVED slots Eric Auger
2016-05-09 22:49 ` Alex Williamson
2016-05-11 12:58 ` Eric Auger
2016-05-04 11:54 ` [PATCH v9 4/7] vfio: allow reserved msi iova registration Eric Auger
2016-05-05 19:22 ` Chalamarla, Tirumalesh
2016-05-09 7:55 ` Eric Auger
2016-05-10 15:29 ` Alex Williamson
2016-05-10 15:34 ` Eric Auger
2016-05-04 11:54 ` [PATCH v9 5/7] vfio/type1: also check IRQ remapping capability at msi domain Eric Auger
2016-05-05 19:23 ` Chalamarla, Tirumalesh
2016-05-09 8:05 ` Eric Auger
2016-05-09 22:49 ` Alex Williamson
2016-05-10 16:10 ` Eric Auger
2016-05-10 17:24 ` Robin Murphy
2016-05-11 8:38 ` Eric Auger
2016-05-11 9:31 ` Robin Murphy
2016-05-11 9:44 ` Eric Auger
2016-05-11 13:48 ` Robin Murphy
2016-05-11 14:37 ` Eric Auger
2016-05-04 11:54 ` [PATCH v9 6/7] iommu/arm-smmu: do not advertise IOMMU_CAP_INTR_REMAP Eric Auger
2016-05-04 11:54 ` [PATCH v9 7/7] vfio/type1: return MSI geometry through VFIO_IOMMU_GET_INFO capability chains Eric Auger
2016-05-04 12:06 ` Eric Auger
2016-05-09 23:03 ` Alex Williamson [this message]
2016-05-10 16:50 ` Eric Auger
2016-05-09 22:49 ` Alex Williamson
2016-05-10 16:36 ` Eric Auger
2016-05-20 16:01 ` [PATCH v9 0/7] KVM PCIe/MSI passthrough on ARM/ARM64: kernel part 3/3: vfio changes Eric Auger
2016-06-08 8:29 ` Auger Eric
2016-06-08 21:06 ` Alex Williamson
2016-06-09 7:55 ` Auger Eric
2016-06-09 19:44 ` Alex Williamson
2016-06-20 15:42 ` Pranav Sawargaonkar
2016-06-20 15:46 ` Pranav Sawargaonkar
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