linux-kernel - Re: [PATCH 0/3] Fix virtio-blk issue with SWIOTLB

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Message-ID: <ac6d83d8-02de-dbdf-e309-3a1115642d50@redhat.com>
Date:   Mon, 14 Jan 2019 20:41:37 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Joerg Roedel <joro@...tes.org>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Jens Axboe <axboe@...nel.dk>,
        virtualization@...ts.linux-foundation.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        iommu@...ts.linux-foundation.org, jfehlig@...e.com,
        jon.grimm@....com, brijesh.singh@....com
Subject: Re: [PATCH 0/3] Fix virtio-blk issue with SWIOTLB


On 2019/1/14 下午5:50, Christoph Hellwig wrote:
> On Mon, Jan 14, 2019 at 05:41:56PM +0800, Jason Wang wrote:
>> On 2019/1/11 下午5:15, Joerg Roedel wrote:
>>> On Fri, Jan 11, 2019 at 11:29:31AM +0800, Jason Wang wrote:
>>>> Just wonder if my understanding is correct IOMMU_PLATFORM must be set for
>>>> all virtio devices under AMD-SEV guests?
>>> Yes, that is correct. Emulated DMA can only happen on the SWIOTLB
>>> aperture, because that memory is not encrypted. The guest bounces the
>>> data then to its encrypted memory.
>>>
>>> Regards,
>>>
>>> 	Joerg
>>
>> Thanks, have you tested vhost-net in this case. I suspect it may not work
> Which brings me back to my pet pevee that we need to take actions
> that virtio uses the proper dma mapping API by default with quirks
> for legacy cases.  The magic bypass it uses is just causing problems
> over problems.


Yes, I fully agree with you. This is probably an exact example of such 
problem.

Thanks