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

[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 <dyoung@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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Re: [PATCH retry] intel-iommu:make identity_map default for crash dump

[David Woodhouse]

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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.

-- 
dwmw2

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

[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

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