Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
IronPort-SDR: rOF89x8Gpn8wmQyncf9T3gtTlwhYQWQqySWipcuSiKPjPgz4GIesihmUmV8UuEsatzwyCipNUM
 PuH7dFQ1yvAw==
IronPort-SDR: M3YsKHaDWz7UDbX8ZjfR5lNn57yOKCtKJGxNvx0P6bF/G4LQXMY+brLeZaZvU9OmE76njqtSIJ
 FJ4I9ZUu56qg==
Cc:     baolu.lu@linux.intel.com,
        Srivatsa Vaddagiri <vatsa@codeaurora.org>,
        tsoni@codeaurora.org, virtio-dev@lists.oasis-open.org,
        konrad.wilk@oracle.com, jan.kiszka@siemens.com,
        jasowang@redhat.com, christoffer.dall@arm.com,
        virtualization@lists.linux-foundation.org, alex.bennee@linaro.org,
        iommu@lists.linux-foundation.org, stefano.stabellini@xilinx.com,
        will@kernel.org, linux-kernel@vger.kernel.org,
        pratikp@codeaurora.org
Subject: Re: [PATCH 5/5] virtio: Add bounce DMA ops
To:     "Michael S. Tsirkin" <mst@redhat.com>
References: <1588073958-1793-1-git-send-email-vatsa@codeaurora.org>
 <1588073958-1793-6-git-send-email-vatsa@codeaurora.org>
 <20200428121232-mutt-send-email-mst@kernel.org>
 <20200428174952.GA5097@quicinc.com>
 <20200428163448-mutt-send-email-mst@kernel.org>
 <275eba4b-dd35-aa95-b2e3-9c5cbf7c6d71@linux.intel.com>
 <20200429004531-mutt-send-email-mst@kernel.org>
From:   Lu Baolu <baolu.lu@linux.intel.com>
Message-ID: <b676430c-65b3-096e-ca48-ceebf10f4b28@linux.intel.com>
Date:   Wed, 29 Apr 2020 13:42:13 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101
 Thunderbird/68.7.0
MIME-Version: 1.0
In-Reply-To: <20200429004531-mutt-send-email-mst@kernel.org>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 2020/4/29 12:57, Michael S. Tsirkin wrote:
> On Wed, Apr 29, 2020 at 10:22:32AM +0800, Lu Baolu wrote:
>> On 2020/4/29 4:41, Michael S. Tsirkin wrote:
>>> On Tue, Apr 28, 2020 at 11:19:52PM +0530, Srivatsa Vaddagiri wrote:
>>>> * Michael S. Tsirkin<mst@redhat.com>  [2020-04-28 12:17:57]:
>>>>
>>>>> Okay, but how is all this virtio specific?  For example, why not allow
>>>>> separate swiotlbs for any type of device?
>>>>> For example, this might make sense if a given device is from a
>>>>> different, less trusted vendor.
>>>> Is swiotlb commonly used for multiple devices that may be on different trust
>>>> boundaries (and not behind a hardware iommu)?
>>> Even a hardware iommu does not imply a 100% security from malicious
>>> hardware. First lots of people use iommu=pt for performance reasons.
>>> Second even without pt, unmaps are often batched, and sub-page buffers
>>> might be used for DMA, so we are not 100% protected at all times.
>>>
>>
>> For untrusted devices, IOMMU is forced on even iommu=pt is used;
> 
> I think you are talking about untrusted *drivers* like with VFIO.

No. I am talking about untrusted devices like thunderbolt peripherals.
We always trust drivers hosted in kernel and the DMA APIs are designed
for them, right?

Please refer to this series.

https://lkml.org/lkml/2019/9/6/39

Best regards,
baolu

> 
> On the other hand, I am talking about things like thunderbolt
> peripherals being less trusted than on-board ones.


> 
> Or possibly even using swiotlb for specific use-cases where
> speed is less of an issue.
> 
> E.g. my wifi is pretty slow anyway, and that card is exposed to
> malicious actors all the time, put just that behind swiotlb
> for security, and leave my graphics card with pt since
> I'm trusting it with secrets anyway.
> 
> 
>> and
>> iotlb flush is in strict mode (no batched flushes); ATS is also not
>> allowed. Swiotlb is used to protect sub-page buffers since IOMMU can
>> only apply page granularity protection. Swiotlb is now used for devices
>> from different trust zone.
>>
>> Best regards,
>> baolu
>