linux-kernel - Re: [PATCH 1/1] iommu/vt-d : clear old root entry for dump kernel

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Date:	Tue, 19 Aug 2014 13:49:17 +0800
From:	"Li, ZhenHua" <zhen-hual@...com>
To:	Joerg Roedel <joro@...tes.org>,
	David Woodhouse <dwmw2@...radead.org>
CC:	"Li, Zhen-Hua" <zhen-hual@...com>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] iommu/vt-d : clear old root entry for dump kernel

I found there are more data need to be cleared for the dump kernel.
So please ignore this patch, I will send out another one.

Thanks
Zhenhua

On 08/19/2014 07:59 AM, Li, Zhen-Hua wrote:
> My debugging result is this:
>
> 1. Clear the old root entry table, dump kernel will choose another
>   memory region for root entry.
> 2. Do NOT clear the old root entry, when dump kernel initializing
> the iommu data structure, it  will allocate memory for root entry,
> this is different from the old address.
>
> If not clear old entry , the error message appears before dump kernel
> finishes the iommu init works, and also appears in other places(before
> device inits).
>
> If I clear the old root entry, the error message disappears before iommu
> init work finish, but still appears in other places.
>
> -----Original Message-----
> From: Li, Zhen-Hua
> Sent: Tuesday, August 19, 2014 7:48 AM
> To: Li, Zhen-Hua; Joerg Roedel
> Cc: David Woodhouse; iommu@...ts.linux-foundation.org; linux-kernel@...r.kernel.org
> Subject: RE: [PATCH 1/1] iommu/vt-d : clear old root entry for dump kernel
>
> When the dump kernel boots, it will initialize iommu again, and the root entry will be allocted
> in another memory region.
>
> That means, no matter kernel clears the old root entry table or not,  the dump kernel will use
> another memory region when iommu initializing.
>
> -----Original Message-----
> From: Li, Zhen-Hua
> Sent: Tuesday, August 19, 2014 7:27 AM
> To: 'Joerg Roedel'
> Cc: David Woodhouse; iommu@...ts.linux-foundation.org; linux-kernel@...r.kernel.org
> Subject: RE: [PATCH 1/1] iommu/vt-d : clear old root entry for dump kernel
>
> : [fault reason 01] Present bit in root entry is clear
> It appears when iommu initializing in the kdump kernel.
>
> -----Original Message-----
> From: Joerg Roedel [mailto:joro@...tes.org]
> Sent: Tuesday, August 19, 2014 7:23 AM
> To: Li, Zhen-Hua
> Cc: David Woodhouse; iommu@...ts.linux-foundation.org; linux-kernel@...r.kernel.org
> Subject: Re: [PATCH 1/1] iommu/vt-d : clear old root entry for dump kernel
>
> On Mon, Aug 18, 2014 at 11:01:56PM +0000, Li, Zhen-Hua wrote:
>> There is a bug when Linux running on an HP large system:
>> 	when kdump kernel runs, the hardware is still using the old
>> root entry. This causes error message when iommu not finished initialization.
> What error message are you seeing? When the kdump kernel boots the iommu
> should be still enabled from the old kernel with the old root-entry. So
> any in-flight DMA initiated from the old kernel can still pass and there
> should be no error messages.
>
> When you clear the root-entry that in-flight DMA might go to another
> random location in system memory or just fail, no?
>
>
> 	Joerg
>

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