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virtio,vhost,pc: features, fixes, cleanups.
Virtio 1.0 support for virtio-mmio. Misc fixes, cleanups. Signed-off-by: Michael S. Tsirkin <mst@redhat.com> -----BEGIN PGP SIGNATURE----- iQEcBAABAgAGBQJdf6eKAAoJECgfDbjSjVRpAHIIAInjiMQmc/9ZOlmdRKZtG7ju StJXT+btc1yy4auLGpdNpwmuO3JpidacMqjWbJrglTrljf1B19hIoSVgcAskBj/N 659oHbuaihcHNkidAOy3Gb8abZ7lOdAr4Q8PQriN4C/Y4T0ln8lNqoxiBz2k5XgJ TRib7U64SzfFwEm/LD/bdaWjTzMc2Oa7/OruDwHO19SE5Pd5Vq2KAvfhzwdBooRk yNZSdpR5dxnS+FOiXCLXybGNc9Ndgcdzs4+cl1Wm8EBqJqZUaMXNGDoJoI6qrUw0 T6RLd0d4YyBTebUafeaE/D+0Qwffm3LLpaYK6l0gQJXPItp5q0xHBmOtgvcUlVU= =OoO7 -----END PGP SIGNATURE----- Merge remote-tracking branch 'remotes/mst/tags/for_upstream' into staging virtio,vhost,pc: features, fixes, cleanups. Virtio 1.0 support for virtio-mmio. Misc fixes, cleanups. Signed-off-by: Michael S. Tsirkin <mst@redhat.com> # gpg: Signature made Mon 16 Sep 2019 16:17:30 BST # gpg: using RSA key 281F0DB8D28D5469 # gpg: Good signature from "Michael S. Tsirkin <mst@kernel.org>" [full] # gpg: aka "Michael S. Tsirkin <mst@redhat.com>" [full] # Primary key fingerprint: 0270 606B 6F3C DF3D 0B17 0970 C350 3912 AFBE 8E67 # Subkey fingerprint: 5D09 FD08 71C8 F85B 94CA 8A0D 281F 0DB8 D28D 5469 * remotes/mst/tags/for_upstream: virtio-mmio: implement modern (v2) personality (virtio-1) virtio pmem: user document intel_iommu: Remove the caching-mode check during flag change pc/q35: Disallow vfio-pci hotplug without VT-d caching mode qdev/machine: Introduce hotplug_allowed hook intel_iommu: Sanity check vfio-pci config on machine init done backends/vhost-user.c: prevent using uninitialized vqs vhost-user-blk: prevent using uninitialized vqs docs/nvdimm: add example on persistent backend setup MAINTAINERS: update virtio-rng and virtio-serial maintainer Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
This commit is contained in:
Peter Maydell
commit
f396411259
12 changed files with 521 additions and 33 deletions
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@ -171,6 +171,35 @@ guest software that this vNVDIMM device contains a region that cannot
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accept persistent writes. In result, for example, the guest Linux
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NVDIMM driver, marks such vNVDIMM device as read-only.
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Backend File Setup Example
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--------------------------
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Here are two examples showing how to setup these persistent backends on
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linux using the tool ndctl [3].
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A. DAX device
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Use the following command to set up /dev/dax0.0 so that the entirety of
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namespace0.0 can be exposed as an emulated NVDIMM to the guest:
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ndctl create-namespace -f -e namespace0.0 -m devdax
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The /dev/dax0.0 could be used directly in "mem-path" option.
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B. DAX file
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Individual files on a DAX host file system can be exposed as emulated
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NVDIMMS. First an fsdax block device is created, partitioned, and then
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mounted with the "dax" mount option:
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ndctl create-namespace -f -e namespace0.0 -m fsdax
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(partition /dev/pmem0 with name pmem0p1)
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mount -o dax /dev/pmem0p1 /mnt
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(create or copy a disk image file with qemu-img(1), cp(1), or dd(1)
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in /mnt)
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Then the new file in /mnt could be used in "mem-path" option.
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NVDIMM Persistence
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------------------
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@ -212,3 +241,5 @@ References
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https://www.snia.org/sites/default/files/technical_work/final/NVMProgrammingModel_v1.2.pdf
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[2] Persistent Memory Development Kit (PMDK), formerly known as NVML project, home page:
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http://pmem.io/pmdk/
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[3] ndctl-create-namespace - provision or reconfigure a namespace
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http://pmem.io/ndctl/ndctl-create-namespace.html
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75
docs/virtio-pmem.rst
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75
docs/virtio-pmem.rst
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@ -0,0 +1,75 @@
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========================
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QEMU virtio pmem
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========================
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This document explains the setup and usage of the virtio pmem device
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which is available since QEMU v4.1.0.
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The virtio pmem device is a paravirtualized persistent memory device
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on regular (i.e non-NVDIMM) storage.
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Usecase
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--------
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Virtio pmem allows to bypass the guest page cache and directly use
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host page cache. This reduces guest memory footprint as the host can
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make efficient memory reclaim decisions under memory pressure.
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o How does virtio-pmem compare to the nvdimm emulation supported by QEMU?
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NVDIMM emulation on regular (i.e. non-NVDIMM) host storage does not
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persist the guest writes as there are no defined semantics in the device
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specification. The virtio pmem device provides guest write persistence
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on non-NVDIMM host storage.
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virtio pmem usage
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-----------------
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A virtio pmem device backed by a memory-backend-file can be created on
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the QEMU command line as in the following example:
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-object memory-backend-file,id=mem1,share,mem-path=./virtio_pmem.img,size=4G
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-device virtio-pmem-pci,memdev=mem1,id=nv1
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where:
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- "object memory-backend-file,id=mem1,share,mem-path=<image>, size=<image size>"
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creates a backend file with the specified size.
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- "device virtio-pmem-pci,id=nvdimm1,memdev=mem1" creates a virtio pmem
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pci device whose storage is provided by above memory backend device.
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Multiple virtio pmem devices can be created if multiple pairs of "-object"
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and "-device" are provided.
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Hotplug
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-------
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Virtio pmem devices can be hotplugged via the QEMU monitor. First, the
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memory backing has to be added via 'object_add'; afterwards, the virtio
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pmem device can be added via 'device_add'.
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For example, the following commands add another 4GB virtio pmem device to
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the guest:
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(qemu) object_add memory-backend-file,id=mem2,share=on,mem-path=virtio_pmem2.img,size=4G
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(qemu) device_add virtio-pmem-pci,id=virtio_pmem2,memdev=mem2
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Guest Data Persistence
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----------------------
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Guest data persistence on non-NVDIMM requires guest userspace applications
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to perform fsync/msync. This is different from a real nvdimm backend where
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no additional fsync/msync is required. This is to persist guest writes in
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host backing file which otherwise remains in host page cache and there is
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risk of losing the data in case of power failure.
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With virtio pmem device, MAP_SYNC mmap flag is not supported. This provides
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a hint to application to perform fsync for write persistence.
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Limitations
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------------
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- Real nvdimm device backend is not supported.
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- virtio pmem hotunplug is not supported.
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- ACPI NVDIMM features like regions/namespaces are not supported.
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- ndctl command is not supported.
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