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    SubjectRE: [PATCH 1/1] iommu/vt-d : clear old root entry for dump kernel
    Date
    : [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@8bytes.org]
    Sent: Tuesday, August 19, 2014 7:23 AM
    To: Li, Zhen-Hua
    Cc: David Woodhouse; iommu@lists.linux-foundation.org; linux-kernel@vger.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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