From: Jason Wang <jasowang@redhat.com>
To: David Gibson <david@gibson.dropbear.id.au>,
Christoph Hellwig <hch@lst.de>
Cc: linux-s390@vger.kernel.org, Janosch Frank <frankja@linux.ibm.com>,
"Michael S. Tsirkin" <mst@redhat.com>,
Cornelia Huck <cohuck@redhat.com>, Ram Pai <linuxram@us.ibm.com>,
linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org,
Halil Pasic <pasic@linux.ibm.com>,
Christian Borntraeger <borntraeger@de.ibm.com>,
iommu@lists.linux-foundation.org,
Michael Mueller <mimu@linux.ibm.com>,
"Lendacky, Thomas" <Thomas.Lendacky@amd.com>,
Viktor Mihajlovski <mihajlov@linux.ibm.com>,
Robin Murphy <robin.murphy@arm.com>
Subject: Re: [PATCH 2/2] virtio: let virtio use DMA API when guest RAM is protected
Date: Fri, 21 Feb 2020 11:41:57 +0800 [thread overview]
Message-ID: <8194d502-07d8-b798-a2b5-606a8c05b895@redhat.com> (raw)
In-Reply-To: <20200221025915.GB2298@umbus.fritz.box>
On 2020/2/21 上午10:59, David Gibson wrote:
> On Thu, Feb 20, 2020 at 05:13:09PM +0100, Christoph Hellwig wrote:
>> On Thu, Feb 20, 2020 at 05:06:06PM +0100, Halil Pasic wrote:
>>> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
>>> index 867c7ebd3f10..fafc8f924955 100644
>>> --- a/drivers/virtio/virtio_ring.c
>>> +++ b/drivers/virtio/virtio_ring.c
>>> @@ -243,6 +243,9 @@ static bool vring_use_dma_api(struct virtio_device *vdev)
>>> if (!virtio_has_iommu_quirk(vdev))
>>> return true;
>>>
>>> + if (force_dma_unencrypted(&vdev->dev))
>>> + return true;
>> Hell no. This is a detail of the platform DMA direct implementation.
>> Drivers have no business looking at this flag, and virtio finally needs
>> to be fixed to use the DMA API properly for everything but legacy devices.
> So, this patch definitely isn't right as it stands, but I'm struggling
> to understand what it is you're saying is the right way.
>
> By "legacy devices" I assume you mean pre-virtio-1.0 devices, that
> lack the F_VERSION_1 feature flag. Is that right? Because I don't
> see how being a legacy device or not relates to use of the DMA API.
>
> I *think* what you are suggesting here is that virtio devices that
> have !F_IOMMU_PLATFORM should have their dma_ops set up so that the
> DMA API treats IOVA==PA, which will satisfy what the device expects.
Can this work for swiotlb?
Thanks
> Then the virtio driver can use the DMA API the same way for both
> F_IOMMU_PLATFORM and !F_IOMMU_PLATFORM devices.
>
> But if that works for !F_IOMMU_PLATFORM_DEVICES+F_VERSION_1 devices,
> then AFAICT it will work equally well for legacy devices.
>
> Using the DMA API for *everything* in virtio, legacy or not, seems
> like a reasonable approach to me. But, AFAICT, that does require the
> DMA layer to have some kind of explicit call to turn on this
> behaviour, which the virtio driver would call during initializsation.
> I don't think we can do it 100% within the DMA layer, because only the
> driver can reasonably know when a device has this weird non-standard
> DMA behaviour.
>
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next prev parent reply other threads:[~2020-02-21 3:42 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-20 16:06 [PATCH 0/2] virtio: decouple protected guest RAM form VIRTIO_F_IOMMU_PLATFORM Halil Pasic
2020-02-20 16:06 ` [PATCH 1/2] mm: move force_dma_unencrypted() to mem_encrypt.h Halil Pasic
2020-02-20 16:11 ` Christoph Hellwig
2020-02-20 16:23 ` Christian Borntraeger
2020-02-20 16:31 ` Christoph Hellwig
2020-02-20 17:00 ` Christian Borntraeger
2020-02-21 3:27 ` David Gibson
2020-02-21 13:06 ` Halil Pasic
2020-02-21 15:48 ` Michael S. Tsirkin
2020-02-21 18:07 ` Halil Pasic
2020-02-24 3:33 ` David Gibson
2020-02-24 18:49 ` Halil Pasic
2020-02-25 18:08 ` Cornelia Huck
2020-02-28 0:23 ` David Gibson
2020-02-20 16:06 ` [PATCH 2/2] virtio: let virtio use DMA API when guest RAM is protected Halil Pasic
2020-02-20 16:13 ` Christoph Hellwig
2020-02-21 2:59 ` David Gibson
2020-02-21 3:41 ` Jason Wang [this message]
2020-02-21 13:31 ` Halil Pasic
2020-02-21 13:27 ` Halil Pasic
2020-02-21 16:36 ` Christoph Hellwig
2020-02-24 6:50 ` David Gibson
2020-02-24 18:59 ` Halil Pasic
2020-02-21 14:33 ` Halil Pasic
2020-02-21 16:39 ` Christoph Hellwig
2020-02-21 18:16 ` Halil Pasic
2020-02-22 19:07 ` Michael S. Tsirkin
2020-02-24 17:16 ` Christoph Hellwig
2020-10-28 14:24 ` Alexander Graf via iommu
2020-10-28 18:01 ` Michael S. Tsirkin
2020-02-20 20:55 ` Michael S. Tsirkin
2020-02-21 1:17 ` Ram Pai
2020-02-21 3:29 ` David Gibson
2020-02-21 13:12 ` Halil Pasic
2020-02-21 15:39 ` Tom Lendacky
2020-02-24 6:40 ` David Gibson
2020-02-21 15:56 ` Michael S. Tsirkin
2020-02-21 16:35 ` Christoph Hellwig
2020-02-21 18:03 ` Halil Pasic
2020-02-20 20:48 ` [PATCH 0/2] virtio: decouple protected guest RAM form VIRTIO_F_IOMMU_PLATFORM Michael S. Tsirkin
2020-02-20 21:29 ` Michael S. Tsirkin
2020-02-21 13:37 ` Halil Pasic
2020-02-20 21:33 ` Michael S. Tsirkin
2020-02-21 13:49 ` Halil Pasic
2020-02-21 16:41 ` Christoph Hellwig
2020-02-24 5:44 ` David Gibson
2020-02-21 6:22 ` Jason Wang
2020-02-21 14:56 ` Halil Pasic
2020-02-24 3:38 ` David Gibson
2020-02-24 4:01 ` Jason Wang
2020-02-24 6:06 ` Michael S. Tsirkin
2020-02-24 6:45 ` Jason Wang
2020-02-24 7:48 ` Michael S. Tsirkin
2020-02-24 9:26 ` Jason Wang
2020-02-24 13:40 ` Michael S. Tsirkin
2020-02-25 3:38 ` Jason Wang
2020-02-24 13:56 ` Halil Pasic
2020-02-25 3:30 ` Jason Wang
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