From: Jason Wang <jasowang@redhat.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org
Subject: Re: [PATCH v2 19/24] vdpa: make sure set_features in invoked for legacy
Date: Fri, 7 Aug 2020 11:00:44 +0800 [thread overview]
Message-ID: <5261b78d-f2db-0f80-34ac-1a834353b13a@redhat.com> (raw)
In-Reply-To: <20200806055818-mutt-send-email-mst@kernel.org>
On 2020/8/6 下午6:00, Michael S. Tsirkin wrote:
> On Thu, Aug 06, 2020 at 03:27:38PM +0800, Jason Wang wrote:
>> On 2020/8/6 下午1:53, Michael S. Tsirkin wrote:
>>> On Thu, Aug 06, 2020 at 11:23:05AM +0800, Jason Wang wrote:
>>>> On 2020/8/5 下午7:40, Michael S. Tsirkin wrote:
>>>>> On Wed, Aug 05, 2020 at 02:14:07PM +0800, Jason Wang wrote:
>>>>>> On 2020/8/4 上午5:00, Michael S. Tsirkin wrote:
>>>>>>> Some legacy guests just assume features are 0 after reset.
>>>>>>> We detect that config space is accessed before features are
>>>>>>> set and set features to 0 automatically.
>>>>>>> Note: some legacy guests might not even access config space, if this is
>>>>>>> reported in the field we might need to catch a kick to handle these.
>>>>>> I wonder whether it's easier to just support modern device?
>>>>>>
>>>>>> Thanks
>>>>> Well hardware vendors are I think interested in supporting legacy
>>>>> guests. Limiting vdpa to modern only would make it uncompetitive.
>>>> My understanding is that, IOMMU_PLATFORM is mandatory for hardware vDPA to
>>>> work.
>>> Hmm I don't really see why. Assume host maps guest memory properly,
>>> VM does not have an IOMMU, legacy guest can just work.
>>
>> Yes, guest may not set IOMMU_PLATFORM.
>>
>>
>>> Care explaining what's wrong with this picture?
>>
>> The problem is virtio_vdpa, without IOMMU_PLATFORM it uses PA which can not
>> work if IOMMU is enabled.
>>
>> Thanks
> So that's a virtio_vdpa limitation.
Probably not, I think this goes back to the long debate of whether to
use DMA API unconditionally. If we did that, we can support legacy
virtio driver.
The vDPA device needs to provide a DMA device and the virtio core and
perform DMA API with that device which should work for all of the cases.
But a big question is, do upstream care about out of tree virtio drivers?
Thanks
> In the same way, if a device
> does not have an on-device iommu *and* is not behind an iommu,
> then vdpa can't bind to it.
>
> But this virtio_vdpa specific hack does not belong in a generic vdpa code.
>
>>>
>>>> So it can only work for modern device ...
>>>>
>>>> Thanks
>>>>
>>>>
>>>>>
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next prev parent reply other threads:[~2020-08-07 3:00 UTC|newest]
Thread overview: 69+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-03 20:58 [PATCH v2 00/24] virtio: config space endian-ness cleanup Michael S. Tsirkin
2020-08-03 20:58 ` [PATCH v2 01/24] virtio_balloon: fix sparse warning Michael S. Tsirkin
2020-08-03 21:25 ` David Hildenbrand
2020-08-04 14:16 ` Cornelia Huck
2020-08-03 20:58 ` [PATCH v2 02/24] virtio_ring: sparse warning fixup Michael S. Tsirkin
2020-08-04 14:18 ` Cornelia Huck
2020-08-03 20:58 ` [PATCH v2 03/24] virtio: allow __virtioXX, __leXX in config space Michael S. Tsirkin
2020-08-04 14:23 ` Cornelia Huck
2020-08-04 14:28 ` Michael S. Tsirkin
2020-08-05 6:28 ` Jason Wang
2020-08-05 11:45 ` Michael S. Tsirkin
2020-08-06 3:37 ` Jason Wang
2020-08-06 5:58 ` Michael S. Tsirkin
2020-08-07 3:26 ` Jason Wang
2020-08-03 20:58 ` [PATCH v2 04/24] virtio_9p: correct tags for config space fields Michael S. Tsirkin
2020-08-04 14:25 ` Cornelia Huck
2020-08-03 20:58 ` [PATCH v2 05/24] virtio_balloon: " Michael S. Tsirkin
2020-08-03 21:26 ` David Hildenbrand
2020-08-04 14:26 ` Cornelia Huck
2020-08-03 20:58 ` [PATCH v2 06/24] virtio_blk: " Michael S. Tsirkin
2020-08-04 14:29 ` Cornelia Huck
2020-08-03 20:59 ` [PATCH v2 07/24] virtio_console: " Michael S. Tsirkin
2020-08-04 14:31 ` Cornelia Huck
2020-08-03 20:59 ` [PATCH v2 08/24] virtio_crypto: " Michael S. Tsirkin
2020-08-04 14:32 ` Cornelia Huck
2020-08-03 20:59 ` [PATCH v2 09/24] virtio_fs: " Michael S. Tsirkin
2020-08-04 13:36 ` Vivek Goyal
2020-08-04 14:33 ` Cornelia Huck
2020-08-03 20:59 ` [PATCH v2 10/24] virtio_gpu: " Michael S. Tsirkin
2020-08-04 14:34 ` Cornelia Huck
2020-08-03 20:59 ` [PATCH v2 11/24] virtio_input: " Michael S. Tsirkin
2020-08-04 6:01 ` Gerd Hoffmann
2020-08-04 14:35 ` Cornelia Huck
2020-08-03 20:59 ` [PATCH v2 12/24] virtio_iommu: " Michael S. Tsirkin
2020-08-04 8:00 ` Jean-Philippe Brucker
2020-08-04 14:36 ` Cornelia Huck
2020-08-03 20:59 ` [PATCH v2 13/24] virtio_mem: " Michael S. Tsirkin
2020-08-03 21:23 ` David Hildenbrand
2020-08-04 14:37 ` Cornelia Huck
2020-08-03 20:59 ` [PATCH v2 14/24] virtio_net: " Michael S. Tsirkin
2020-08-04 14:44 ` Cornelia Huck
2020-08-05 13:26 ` Michael S. Tsirkin
2020-08-03 20:59 ` [PATCH v2 15/24] virtio_pmem: " Michael S. Tsirkin
2020-08-04 14:46 ` Cornelia Huck
2020-08-03 20:59 ` [PATCH v2 16/24] virtio_scsi: " Michael S. Tsirkin
2020-08-04 14:48 ` Cornelia Huck
2020-08-03 20:59 ` [PATCH v2 17/24] virtio_config: disallow native type fields Michael S. Tsirkin
2020-08-04 14:50 ` Cornelia Huck
2020-08-05 13:29 ` Michael S. Tsirkin
2020-08-03 21:00 ` [PATCH v2 18/24] mlxbf-tmfifo: sparse tags for config access Michael S. Tsirkin
2020-08-04 14:56 ` Cornelia Huck
2020-08-05 13:29 ` Michael S. Tsirkin
2020-08-03 21:00 ` [PATCH v2 19/24] vdpa: make sure set_features in invoked for legacy Michael S. Tsirkin
2020-08-05 6:14 ` Jason Wang
2020-08-05 11:40 ` Michael S. Tsirkin
2020-08-06 3:23 ` Jason Wang
2020-08-06 5:53 ` Michael S. Tsirkin
2020-08-06 7:27 ` Jason Wang
2020-08-06 10:00 ` Michael S. Tsirkin
2020-08-07 3:00 ` Jason Wang [this message]
2020-08-03 21:00 ` [PATCH v2 20/24] vhost/vdpa: switch to new helpers Michael S. Tsirkin
2020-08-03 21:00 ` [PATCH v2 21/24] virtio_vdpa: legacy features handling Michael S. Tsirkin
2020-08-03 21:00 ` [PATCH v2 22/24] vdpa_sim: fix endian-ness of config space Michael S. Tsirkin
2020-08-05 6:21 ` Jason Wang
2020-08-05 11:44 ` Michael S. Tsirkin
2020-08-05 12:06 ` Michael S. Tsirkin
2020-08-06 3:23 ` Jason Wang
2020-08-03 21:00 ` [PATCH v2 23/24] virtio_config: cread/write cleanup Michael S. Tsirkin
2020-08-03 21:00 ` [PATCH v2 24/24] virtio_config: rewrite using _Generic Michael S. Tsirkin
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