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

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Date:	Mon, 22 Apr 2013 16:06:45 +0900
From:	Takao Indoh <indou.takao@...fujitsu.com>
To:	wei@...stanetworks.com
CC:	dwmw2@...radead.org, iommu@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] intel-iommu: Disable DMA Remapping when intel_iommu=off

(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

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