[PATCH retry] intel-iommu:make identity_map default for crash dump

[Dave Young]

kdump kernel sometimes will get DMAR faults which
is caused by random in-flight dma from 1st kernel

Here make the identity_mapping as default for this case

Signed-off-by: Dave Young <dyo...@redhat.com>
---
drivers/iommu/intel-iommu.c | 3 ++-
1 files changed, 2 insertions(+), 1 deletions(-)

--- linux-2.6.orig/drivers/iommu/intel-iommu.c 2011-11-01 13:06:18.667505962 +0800
+++ linux-2.6/drivers/iommu/intel-iommu.c 2011-11-01 17:07:50.789137864 +0800
@@ -40,6 +40,7 @@
#include <linux/tboot.h>
#include <linux/dmi.h>
#include <linux/pci-ats.h>
+#include <linux/crash_dump.h>
#include <asm/cacheflush.h>
#include <asm/iommu.h>

@@ -2488,7 +2489,7 @@ static int __init init_dmars(void)
}
}

- if (iommu_pass_through)
+ if (iommu_pass_through || is_kdump_kernel())
iommu_identity_mapping |= IDENTMAP_ALL;

#ifdef CONFIG_INTEL_IOMMU_BROKEN_GFX_WA
--
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[Dave Young]

On 11/01/2011 05:34 PM, David Woodhouse wrote:

> On Tue, 2011-11-01 at 17:19 +0800, Dave Young wrote:
>> kdump kernel sometimes will get DMAR faults which
>> is caused by random in-flight dma from 1st kernel
>>
>> Here make the identity_mapping as default for this case
>

> So you want to *allow* the random in-flight DMA? And with an identity
> mapping it's really going to random addresses, since it'll be
> untranslated and won't even go to the physical addresses which it was
> originally intended for?
>
> This seems entirely broken to me.
>
> If there is "random in-flight dma" from the first kernel, the correct
> thing to do is *block* it. Which is what we do.
>


This patch works for me for several cases. For kdump It can be seen a
workaround. But yes blocking the 1st kernel dma is ideal.

Glad to hear that you are working on this.

--
Thanks
Dave