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Subject: Re: [PATCH v2 1/1] fs/splice: add missing callback for inaccessible
 pages
To:     Christian Borntraeger <borntraeger@de.ibm.com>,
        Ulrich Weigand <uweigand@de.ibm.com>
Cc:     Claudio Imbrenda <imbrenda@linux.ibm.com>, viro@zeniv.linux.org.uk,
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        peterz@infradead.org, sean.j.christopherson@intel.com,
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Message-ID: <fcc9adea-598f-f882-c3e3-09d190cd5d52@intel.com>
Date:   Tue, 5 May 2020 07:34:39 -0700
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Sender: linux-kernel-owner@vger.kernel.org
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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.