linux-kernel - Re: [PATCH 1/1] intel-iommu: Disable DMA Remapping when intel

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Message-ID: <CANwcMEZsH5YeuucyXLeA3MWE8tApAbLLzkkT=26cDZU=Y0yhtw@mail.gmail.com>
Date:	Mon, 22 Apr 2013 00:11:33 -0700
From:	Wei Hu <wei@...stanetworks.com>
To:	Takao Indoh <indou.takao@...fujitsu.com>
Cc:	dwmw2 <dwmw2@...radead.org>,
	iommu <iommu@...ts.linux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] intel-iommu: Disable DMA Remapping when intel_iommu=off

On Mon, Apr 22, 2013 at 12:06 AM, Takao Indoh
<indou.takao@...fujitsu.com> wrote:
> (2013/04/22 15:50), Wei Hu wrote:
>> On Sun, Apr 21, 2013 at 10:31 PM, Takao Indoh
>> <indou.takao@...fujitsu.com> wrote:
>>> (2013/04/20 15:58), Wei Hu wrote:
>>>> On a VT-d capable machine Linux will enable IOMMU by default. If it
>>>> then kexec's a second kernel with intel_iommu=off, this second kernel
>>>> will leave the DMA remapping engine on with no code handling it. The
>>>> symptom is at least USB and SATA drives stop working. This patch fixes
>>>> the problem by always disabling DMA remapping when intel_iommu=off.
>>>
>>> Even when second kernel boots up with intel_iommu=on, dma-remapping need
>>> to be disabled as well before it is initialized and enabled again in
>>> init_dmars(). So, how about something like this?
>>>
>>>          for_each_drhd_unit(drhd) {
>>>                  struct dmar_drhd_unit *drhd;
>>>                  if (drhd->ignored)
>>>                          continue;
>>>
>>>                  iommu = drhd->iommu;
>>>                  if (iommu->gcmd & DMA_GCMD_TE)
>>>                          iommu_disable_translation(iommu);
>>>          }
>>>
>>> Note, if you agree above code and fix your patch like this, you need
>>> additinal fix to set iommu->gcmd flag sinse gcmd is always zero here.
>>> See first hunk of this patch.
>>> https://lkml.org/lkml/2013/3/20/707
>>
>> Thanks for your reply. I reviewed your patch. Are you suggesting
>> keeping your change to dmar.c, and moving your change to intel-iommu.c
>> (i.e. the code you just showed) up after the call to
>> dmar_table_init()?
>>
>
> Yes, exactly.
>
> Thanks,
> Takao Indoh
>

Sounds great. If you want to make the change and get your patch
accepted that's fine with me.
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