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

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Date:	Sun, 21 Apr 2013 23:50:56 -0700
From:	Wei Hu <wei@...stanetworks.com>
To:	Takao Indoh <indou.takao@...fujitsu.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

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()?
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