linux-kernel - Re: [PATCH v8 02/10] iommu/vt-d: Items required for kdump

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Date:	Mon, 12 Jan 2015 16:22:08 +0100
From:	Joerg Roedel <joro@...tes.org>
To:	"Li, Zhen-Hua" <zhen-hual@...com>
Cc:	dwmw2@...radead.org, indou.takao@...fujitsu.com, bhe@...hat.com,
	vgoyal@...hat.com, dyoung@...hat.com,
	iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, kexec@...ts.infradead.org,
	alex.williamson@...hat.com, ddutile@...hat.com,
	ishii.hironobu@...fujitsu.com, bhelgaas@...gle.com,
	doug.hatch@...com, jerry.hoemann@...com, tom.vaden@...com,
	li.zhang6@...com, lisa.mitchell@...com, billsumnerlinux@...il.com,
	rwright@...com
Subject: Re: [PATCH v8 02/10] iommu/vt-d: Items required for kdump

On Mon, Jan 12, 2015 at 03:06:20PM +0800, Li, Zhen-Hua wrote:
> +
> +#ifdef CONFIG_CRASH_DUMP
> +
> +/*
> + * Fix Crashdump failure caused by leftover DMA through a hardware IOMMU
> + *
> + * Fixes the crashdump kernel to deal with an active iommu and legacy
> + * DMA from the (old) panicked kernel in a manner similar to how legacy
> + * DMA is handled when no hardware iommu was in use by the old kernel --
> + * allow the legacy DMA to continue into its current buffers.
> + *
> + * In the crashdump kernel, this code:
> + * 1. skips disabling the IOMMU's translating of IO Virtual Addresses (IOVA).
> + * 2. Do not re-enable IOMMU's translating.
> + * 3. In kdump kernel, use the old root entry table.
> + * 4. Leaves the current translations in-place so that legacy DMA will
> + *    continue to use its current buffers.
> + * 5. Allocates to the device drivers in the crashdump kernel
> + *    portions of the iova address ranges that are different
> + *    from the iova address ranges that were being used by the old kernel
> + *    at the time of the panic.
> + *
> + */

It looks like you are still copying the io-page-tables from the old
kernel into the kdump kernel, is that right? With the approach that was
proposed you only need to copy over the context entries 1-1. They are
still pointing to the page-tables in the old kernels memory (which is
just fine).

The root-entry of the old kernel is also re-used, and when the kdump
kernel starts to use a device, its context entry is updated to point to
a newly allocated page-table.


	Joerg

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