Re: [PATCH v2 1/1] fs/splice: add missing callback for inaccessible pages

[Dave Hansen]

On 5/5/20 7:31 AM, Christian Borntraeger wrote:
>> So, the requirements are:
>>
>> 1. Allow host-side DMA and CPU access to shared pages
>> 2. Stop host-side DMA and CPU access to encrypted pages
>> 3. Allow pages to be converted between the states at the request of the
>>    guest
>>
>> Stopping the DMA is pretty easy, even across the gazillions of drivers
>> in the tree because even random ethernet drivers do stuff like:
>>
>>                 txdr->buffer_info[i].dma =
>>                         dma_map_single(&pdev->dev, skb->data, skb->len,
>>                                        DMA_TO_DEVICE);
>>
>> So the DMA can be stopped at the mapping layer.  It's a *LOT* easier to
>> catch there since the IOMMUs already provide isolation between the I/O
>> and CPU address spaces.
> And your problem is that the guest could convert this after the dma_map?
> So you looked into our code if this would help?

Yep, it seemed like a close-enough problem.