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From: Auger Eric <eric.auger@redhat.com>
To: Peter Maydell <peter.maydell@linaro.org>,
	Andrew Jones <drjones@redhat.com>
Cc: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>,
	"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
	"qemu-arm@nongnu.org" <qemu-arm@nongnu.org>,
	Jonathan Cameron <jonathan.cameron@huawei.com>,
	Linuxarm <linuxarm@huawei.com>,
	"alex.williamson@redhat.com" <alex.williamson@redhat.com>,
	Zhaoshenglong <zhaoshenglong@huawei.com>,
	"imammedo@redhat.com" <imammedo@redhat.com>
Subject: Re: [Qemu-devel] [RFC v2 6/6] hw/arm: Populate non-contiguous memory regions
Date: Fri, 15 Jun 2018 18:13:28 +0200	[thread overview]
Message-ID: <333cd485-dc75-d295-16fd-98a1108e1e15@redhat.com> (raw)
In-Reply-To: <CAFEAcA-nG4Xv=PmxzW3tzs-TStziMDHMFxYi6_teSe1GhLH=hw@mail.gmail.com>

Hi,

On 06/15/2018 05:54 PM, Peter Maydell wrote:
> Why should the VM ever care about where the address regions in the
> host happen to be when it comes to where it's putting its RAM
> in the VM's address layout? I feel like I'm missing something here...
> 
> thanks

The VM cannot use RAM GPA that matches assigned device reserved IOVA
regions. When you assign a device, the whole VM RAM is mapped in the
physical IOMMU and IOVA corresponds to GPA. but sometimes some IOVA
cannot be used due to the host specificities and especially iommu
peculiarities. Some IOVAs may be simply "bypassed" by the iommu, like on
x86 and also with some ARM SMMU integration. In such a case the DMA
accesses have no chance to reach the guest RAM as expected. Hope it
clarifies.

Thanks

Eric

  reply	other threads:[~2018-06-15 16:13 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-16 15:20 [Qemu-devel] [RFC v2 0/6] hw/arm: Add support for non-contiguous iova regions Shameer Kolothum
2018-05-16 15:20 ` [Qemu-devel] [RFC v2 1/6] hw/vfio: Retrieve valid iova ranges from kernel Shameer Kolothum
2018-05-28 14:21   ` Auger Eric
2018-05-30 14:43     ` Shameerali Kolothum Thodi
2018-05-16 15:20 ` [Qemu-devel] [RFC v2 2/6] hw/arm/virt: Enable dynamic generation of guest RAM memory regions Shameer Kolothum
2018-05-28 14:21   ` Auger Eric
2018-05-30 14:43     ` Shameerali Kolothum Thodi
2018-05-28 16:47   ` Andrew Jones
2018-05-30 14:50     ` Shameerali Kolothum Thodi
2018-05-16 15:20 ` [Qemu-devel] [RFC v2 3/6] hw/arm/virt: Add pc-dimm mem hotplug framework Shameer Kolothum
2018-05-28 14:21   ` Auger Eric
2018-05-30 14:46     ` Shameerali Kolothum Thodi
2018-05-16 15:20 ` [Qemu-devel] [RFC v2 4/6] hw/arm: Changes required to accommodate non-contiguous DT mem nodes Shameer Kolothum
2018-05-28 14:21   ` Auger Eric
2018-05-30 14:46     ` Shameerali Kolothum Thodi
2018-05-16 15:20 ` [Qemu-devel] [RFC v2 5/6] hw/arm: ACPI SRAT changes to accommodate non-contiguous mem Shameer Kolothum
2018-05-28 14:21   ` Auger Eric
2018-05-28 17:02   ` Andrew Jones
2018-05-30 14:51     ` Shameerali Kolothum Thodi
2018-05-31 20:15     ` Auger Eric
2018-06-01 11:09       ` Shameerali Kolothum Thodi
2018-05-16 15:20 ` [Qemu-devel] [RFC v2 6/6] hw/arm: Populate non-contiguous memory regions Shameer Kolothum
2018-05-28 14:21   ` Auger Eric
2018-05-30 14:48     ` Shameerali Kolothum Thodi
2018-06-05  7:49     ` Shameerali Kolothum Thodi
2018-06-15 15:44       ` Andrew Jones
2018-06-15 15:54         ` Peter Maydell
2018-06-15 16:13           ` Auger Eric [this message]
2018-06-15 16:33             ` Peter Maydell
2018-06-18  9:46               ` Shameerali Kolothum Thodi
2018-06-15 15:55         ` Auger Eric
2018-05-28 14:22 ` [Qemu-devel] [RFC v2 0/6] hw/arm: Add support for non-contiguous iova regions Auger Eric
2018-05-30 14:39   ` Shameerali Kolothum Thodi
2018-05-30 15:24     ` Auger Eric

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