Re: SMMU, Unhandled context fault

From: Julien Grall <julien.grall@arm.com>
To: Peng Fan <van.freenix@gmail.com>
Cc: "Edgar E. Iglesias" <edgar.iglesias@gmail.com>,
	sstabellini@kernel.org, xen-devel@lists.xenproject.org
Subject: Re: SMMU, Unhandled context fault
Date: Thu, 28 Apr 2016 14:14:58 +0100	[thread overview]
Message-ID: <57220CD2.9060905@arm.com> (raw)
In-Reply-To: <20160428125612.GA29682@linux-7smt.suse>

Hello,

On 28/04/16 13:56, Peng Fan wrote:
> On Thu, Apr 28, 2016 at 11:27:22AM +0100, Julien Grall wrote:
>>
>>
>> On 28/04/16 07:39, Peng Fan wrote:
>>> Hi Julien,
>>
>> Hello Peng,
>>
>>> On Thu, Apr 28, 2016 at 10:37:54AM +0800, Peng Fan wrote:
>>>> Hi Julien,
>>>> On Wed, Apr 27, 2016 at 10:58:28AM +0100, Julien Grall wrote:
>>>>> Hello Peng,
>>>>>
>>>>> On 27/04/2016 03:02, Peng Fan wrote:
>>>>>> On Tue, Apr 26, 2016 at 04:30:03PM +0200, Edgar E. Iglesias wrote:
>>>>>>> On Tue, Apr 26, 2016 at 09:56:33PM +0800, Peng Fan wrote:
>>>>>>>> You mean the PNU bit(Privileged Not Unprivileged) is 1?
>>>>>>>> I did not met Unhandled context fault each time.
>>>>>>>> Actually during my serveral boot test, I only met two times.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> I meant the NSSTATE and NSATTR bits in FSYNR are set to zero. I get the
>>>>>>> impression that the TrustZone state for the SD controller may be
>>>>>>
>>>>>> oh. The NSATTR bit is 0. I did not find NSSTATE in my Issue D SMMU spec.
>>>>>> If without xen, only one linux boots up, sd controller can access memory using
>>>>>> DMA without issue.
>>>>>
>>>>> IIRC, by default Linux baremetal does not protect the devices with the SMMU.
>>>>>
>>>>> I would recommend you to check whether the SMMUs are in-used and configured
>>>>> to generate a fault (disable_bypass = 1).
>>>>
>>>> Ok. I'll set S2CRn to generate fault in xen smmu driver to see whether SMMUs in-used or not
>>
>> I meant in Linux.
>
> My bad. Do you mean enabling SMMU driver in Linux with KVM support?

Yes.

[...]

> Is there any big difference between XEN SMMU driver and linux SMMU driver?
> I know that XEN only support Stage 2. But the initliaization flow is almost the same.

The SMMU driver for Xen is a port from Linux 3.19-rc0. Since then the 
Linux driver has been reworked and it might be possible that we have 
missed some bug fix.

Aside that, for Xen, the page tables are always shared between the SMMU 
and the processor.

Regards,

-- 
Julien Grall

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