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Re: [Qemu-devel] KVM "fake DAX" flushing interface - discussion
From: |
Dan Williams |
Subject: |
Re: [Qemu-devel] KVM "fake DAX" flushing interface - discussion |
Date: |
Thu, 2 Nov 2017 09:30:16 -0700 |
On Thu, Nov 2, 2017 at 1:50 AM, Xiao Guangrong
<address@hidden> wrote:
[..]
>> Yes, the GUID will specifically identify this range as "Virtio Shared
>> Memory" (or whatever name survives after a bikeshed debate). The
>> libnvdimm core then needs to grow a new region type that mostly
>> behaves the same as a "pmem" region, but drivers/nvdimm/pmem.c grows a
>> new flush interface to perform the host communication. Device-dax
>> would be disallowed from attaching to this region type, or we could
>> grow a new device-dax type that does not allow the raw device to be
>> mapped, but allows a filesystem mounted on top to manage the flush
>> interface.
>
>
> I am afraid it is not a good idea that a single SPA is used for multiple
> purposes. For the region used as "pmem" is directly mapped to the VM so
> that guest can freely access it without host's assistance, however, for
> the region used as "host communication" is not mapped to VM, so that
> it causes VM-exit and host gets the chance to do specific operations,
> e.g, flush cache. So we'd better distinctly define these two regions to
> avoid the unnecessary complexity in hypervisor.
Good point, I was assuming that the mmio flush interface would be
discovered separately from the NFIT-defined memory range. Perhaps via
PCI in the guest? This piece of the proposal needs a bit more
thought...
- Re: [Qemu-devel] KVM "fake DAX" flushing interface - discussion, Dan Williams, 2017/11/01
- Re: [Qemu-devel] KVM "fake DAX" flushing interface - discussion, Xiao Guangrong, 2017/11/01
- Re: [Qemu-devel] KVM "fake DAX" flushing interface - discussion, Dan Williams, 2017/11/01
- Re: [Qemu-devel] KVM "fake DAX" flushing interface - discussion, Xiao Guangrong, 2017/11/02
- Re: [Qemu-devel] KVM "fake DAX" flushing interface - discussion,
Dan Williams <=
- Re: [Qemu-devel] KVM "fake DAX" flushing interface - discussion, Xiao Guangrong, 2017/11/03
- Re: [Qemu-devel] KVM "fake DAX" flushing interface - discussion, Rik van Riel, 2017/11/21
- Re: [Qemu-devel] KVM "fake DAX" flushing interface - discussion, Dan Williams, 2017/11/21
- Re: [Qemu-devel] KVM "fake DAX" flushing interface - discussion, Rik van Riel, 2017/11/21
- Re: [Qemu-devel] KVM "fake DAX" flushing interface - discussion, Xiao Guangrong, 2017/11/22
- Re: [Qemu-devel] KVM "fake DAX" flushing interface - discussion, Dan Williams, 2017/11/23
- Re: [Qemu-devel] KVM "fake DAX" flushing interface - discussion, Paolo Bonzini, 2017/11/23
- Re: [Qemu-devel] KVM "fake DAX" flushing interface - discussion, Pankaj Gupta, 2017/11/24
- Re: [Qemu-devel] KVM "fake DAX" flushing interface - discussion, Paolo Bonzini, 2017/11/24
- Re: [Qemu-devel] KVM "fake DAX" flushing interface - discussion, Pankaj Gupta, 2017/11/24