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Re: [PATCH v4 11/11] vfio: Disable only uncoordinated discards
From: |
David Hildenbrand |
Subject: |
Re: [PATCH v4 11/11] vfio: Disable only uncoordinated discards |
Date: |
Thu, 14 Jan 2021 17:19:02 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 |
On 14.01.21 00:57, Alex Williamson wrote:
> On Thu, 7 Jan 2021 14:34:23 +0100
> David Hildenbrand <david@redhat.com> wrote:
>
>> We support coordinated discarding of RAM using the RamDiscardMgr. Let's
>> unlock support for coordinated discards, keeping uncoordinated discards
>> (e.g., via virtio-balloon) disabled.
>>
>> This unlocks virtio-mem + vfio. Note that vfio used via "nvme://" by the
>> block layer has to be implemented/unlocked separately. For now,
>> virtio-mem only supports x86-64 - spapr IOMMUs are not tested/affected.
>
> I think SPAPR always uses a vIOMMU, but I won't claim to understand it.
I heard about that, but I also know that they are using virtio-balloon.
Theoretically, virtio-balloon does currently not support vIOMMUs
(iommu=on results in the balloon device essentially being disable).
> Is there anything other than testing that restricts it to x86-64? ARM
I am not aware, but well, I guess we'll learn as we go/unlock virtio-mem
on these architectures.
Jonathan is trying to enable arm64 support for virtio-mem. I asked him
to test vfio.
I'll have to cleanup my s390x prototype and find a machine to test with
vfio.
> and S390 will use the same type1 IOMMU backend as far as vfio support
> is concerned. Should we do something more than put it in a commit log
> if we really want to prevent it elsewhere? Thanks,
I think it should be sufficient to have it in the logs for now. I'll be
involved when unlocking virtio-mem on other archs and will request to
test vfio. In case we find issues, we should try fixing them first
(instead of fencing it / bailing out).
Obviously, this won't stop other RamDiscardMgr users from popping up,
but I guess we'll stumble over that as well.
--
Thanks,
David / dhildenb
- Re: [PATCH v4 05/11] vfio: Query and store the maximum number of possible DMA mappings, (continued)
- [PATCH v4 06/11] vfio: Sanity check maximum number of DMA mappings with RamDiscardMgr, David Hildenbrand, 2021/01/07
- [PATCH v4 08/11] softmmu/physmem: Don't use atomic operations in ram_block_discard_(disable|require), David Hildenbrand, 2021/01/07
- [PATCH v4 07/11] vfio: Support for RamDiscardMgr in the vIOMMU case, David Hildenbrand, 2021/01/07
- [PATCH v4 09/11] softmmu/physmem: Extend ram_block_discard_(require|disable) by two discard types, David Hildenbrand, 2021/01/07
- [PATCH v4 10/11] virtio-mem: Require only coordinated discards, David Hildenbrand, 2021/01/07
- [PATCH v4 11/11] vfio: Disable only uncoordinated discards, David Hildenbrand, 2021/01/07