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From: Will Deacon <will.deacon@arm.com>
To: Alex Williamson <alex.williamson@redhat.com>
Cc: Christoffer Dall <christoffer.dall@linaro.org>,
	Don Dutile <ddutile@redhat.com>,
	Eric Auger <eric.auger@redhat.com>,
	eric.auger.pro@gmail.com, marc.zyngier@arm.com,
	robin.murphy@arm.com, joro@8bytes.org, tglx@linutronix.de,
	jason@lakedaemon.net, linux-arm-kernel@lists.infradead.org,
	kvm@vger.kernel.org, drjones@redhat.com,
	linux-kernel@vger.kernel.org, pranav.sawargaonkar@gmail.com,
	iommu@lists.linux-foundation.org, punit.agrawal@arm.com,
	diana.craciun@nxp.com, benh@kernel.crashing.org, arnd@arndb.de,
	jcm@redhat.com, dwmw@amazon.co.uk
Subject: Re: Summary of LPC guest MSI discussion in Santa Fe
Date: Wed, 9 Nov 2016 22:25:22 +0000	[thread overview]
Message-ID: <20161109222522.GS17771@arm.com> (raw)
In-Reply-To: <20161109151709.74927f83@t450s.home>

On Wed, Nov 09, 2016 at 03:17:09PM -0700, Alex Williamson wrote:
> On Wed, 9 Nov 2016 20:31:45 +0000
> Will Deacon <will.deacon@arm.com> wrote:
> > On Wed, Nov 09, 2016 at 08:23:03PM +0100, Christoffer Dall wrote:
> > > 
> > > (I suppose it's technically possible to get around this issue by letting
> > > QEMU place RAM wherever it wants but tell the guest to never use a
> > > particular subset of its RAM for DMA, because that would conflict with
> > > the doorbell IOVA or be seen as p2p transactions.  But I think we all
> > > probably agree that it's a disgusting idea.)  
> > 
> > Disgusting, yes, but Ben's idea of hotplugging on the host controller with
> > firmware tables describing the reserved regions is something that we could
> > do in the distant future. In the meantime, I don't think that VFIO should
> > explicitly reject overlapping mappings if userspace asks for them.
> 
> I'm confused by the last sentence here, rejecting user mappings that
> overlap reserved ranges, such as MSI doorbell pages, is exactly how
> we'd reject hot-adding a device when we meet such a conflict.  If we
> don't reject such a mapping, we're knowingly creating a situation that
> potentially leads to data loss.  Minimally, QEMU would need to know
> about the reserved region, map around it through VFIO, and take
> responsibility (somehow) for making sure that region is never used for
> DMA.  Thanks,

Yes, but my point is that it should be up to QEMU to abort the hotplug, not
the host kernel, since there may be ways in which a guest can tolerate the
overlapping region (e.g. by avoiding that range of memory for DMA).

Will

  reply	other threads:[~2016-11-09 22:25 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-11-03 21:39 [RFC 0/8] KVM PCIe/MSI passthrough on ARM/ARM64 (Alt II) Eric Auger
2016-11-03 21:39 ` [RFC 1/8] vfio: fix vfio_info_cap_add/shift Eric Auger
2016-11-03 21:39 ` [RFC 2/8] iommu/iova: fix __alloc_and_insert_iova_range Eric Auger
2016-11-03 21:39 ` [RFC 3/8] iommu/dma: Allow MSI-only cookies Eric Auger
2016-11-03 21:39 ` [RFC 4/8] iommu: Add a list of iommu_reserved_region in iommu_domain Eric Auger
2016-11-03 21:39 ` [RFC 5/8] vfio/type1: Introduce RESV_IOVA_RANGE capability Eric Auger
2016-11-03 21:39 ` [RFC 6/8] iommu: Handle the list of reserved regions Eric Auger
2016-11-03 21:39 ` [RFC 7/8] iommu/vt-d: Implement add_reserved_regions callback Eric Auger
2016-11-03 21:39 ` [RFC 8/8] iommu/arm-smmu: implement " Eric Auger
2016-11-04  4:02 ` [RFC 0/8] KVM PCIe/MSI passthrough on ARM/ARM64 (Alt II) Alex Williamson
2016-11-08  2:45   ` Summary of LPC guest MSI discussion in Santa Fe (was: Re: [RFC 0/8] KVM PCIe/MSI passthrough on ARM/ARM64 (Alt II)) Will Deacon
2016-11-08 14:27     ` Summary of LPC guest MSI discussion in Santa Fe Auger Eric
2016-11-08 17:54       ` Will Deacon
2016-11-08 19:02         ` Don Dutile
2016-11-08 19:10           ` Will Deacon
2016-11-09  7:43           ` Auger Eric
2016-11-08 16:02     ` Don Dutile
2016-11-08 20:29     ` Summary of LPC guest MSI discussion in Santa Fe (was: Re: [RFC 0/8] KVM PCIe/MSI passthrough on ARM/ARM64 (Alt II)) Christoffer Dall
2016-11-08 23:35       ` Alex Williamson
2016-11-09  2:52         ` Summary of LPC guest MSI discussion in Santa Fe Don Dutile
2016-11-09 17:03           ` Will Deacon
2016-11-09 18:59             ` Don Dutile
2016-11-09 19:23               ` Christoffer Dall
2016-11-09 20:01                 ` Alex Williamson
2016-11-10 14:40                   ` Joerg Roedel
2016-11-10 17:07                     ` Alex Williamson
2016-11-09 20:31                 ` Will Deacon
2016-11-09 22:17                   ` Alex Williamson
2016-11-09 22:25                     ` Will Deacon [this message]
2016-11-09 23:24                       ` Alex Williamson
2016-11-09 23:38                         ` Will Deacon
2016-11-09 23:59                           ` Alex Williamson
2016-11-10  0:14                             ` Auger Eric
2016-11-10  0:55                               ` Alex Williamson
2016-11-10  2:01                                 ` Will Deacon
2016-11-10 11:14                                   ` Auger Eric
2016-11-10 17:46                                     ` Alex Williamson
2016-11-11 11:19                                       ` Joerg Roedel
2016-11-11 15:50                                         ` Alex Williamson
2016-11-11 16:05                                           ` Alex Williamson
2016-11-14 15:19                                             ` Joerg Roedel
2016-11-11 16:25                                           ` Don Dutile
2016-11-11 16:00                                         ` Don Dutile
2016-11-10 14:52                               ` Joerg Roedel
2016-11-09 20:11               ` Robin Murphy
2016-11-10 15:18                 ` Joerg Roedel
2016-11-21  5:13     ` Jon Masters
2016-11-23 20:12       ` Don Dutile

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