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Re: [Qemu-devel] [PATCH 0/2] add "nopin" option in the memory-backend-fi
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From: |
Alex Williamson |
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Subject: |
Re: [Qemu-devel] [PATCH 0/2] add "nopin" option in the memory-backend-file |
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Date: |
Mon, 16 Oct 2017 09:47:54 -0600 |
On Mon, 16 Oct 2017 16:56:21 +0800
Yang Zhong <address@hidden> wrote:
> Qemu does not need pin NVDIMM memory for VFIO device during VFIO
> hotplug, what's more, if there is no NVDIMM hw in the test machine,
> the VFIO hotplug operation will need at least 10 minutes to pin RAM
> as the NVDIMM, this time is not accepted. So we add "nopin=on" option
> in the memory-backed-file, which can avoid to pin RAM memory for NVDIMM.
>
> The new command like below:
> -object
> memory-backend-file,id=mem0,share,nopin=on,mem-path=kvm.img,size=9161408512
>
> The default of "nopin" still "off" value, which is same with previous value.
If an NVDIMM is not a possible DMA target for a VFIO assigned device
then it should be in a different AddressSpace from the device. If an
NVDIMM can be a DMA target then it's the correct thing to do to pin it
through the IOMMU for a VFIO device even if it might take considerable
time to do so. Thanks,
Alex