linux-kernel - Re: [PATCH v11 08/10] iommu/vt-d: assign new page table for dma

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Date:	Thu, 21 May 2015 18:11:10 +0800
From:	Baoquan He <bhe@...hat.com>
To:	"Li, ZhenHua" <zhen-hual@...com>
Cc:	dwmw2@...radead.org, indou.takao@...fujitsu.com, joro@...tes.org,
	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 v11 08/10] iommu/vt-d: assign new page table for dma_map

On 05/21/15 at 04:40pm, Li, ZhenHua wrote:
> Hi Baoquan,
> During driver being loaded and initialized, when there is a new dma
> request, the function
>                __get_valid_domain_for_dev
> is called, and then new page is mapped.
> 
> Please check this:
> struct dma_map_ops intel_dma_ops = {
>         .alloc = intel_alloc_coherent,
>         .free = intel_free_coherent,
>         .map_sg = intel_map_sg,
>         .unmap_sg = intel_unmap_sg,
>         .map_page = intel_map_page,
>         .unmap_page = intel_unmap_page,
>         .mapping_error = intel_mapping_error,
> };
> 
> You can also add dump_stack() in __get_valid_domain_for_dev to debug.

Yeah, I saw that. At the beginning I am just wondering why you say a new
page-table, and also mention it's a empty page-table. I think here that
new page-table is an empty page-table when you said them.

No confusion any more. Thanks for explanation.

> 
> Thanks
> Zhenhua
> 
> On 05/21/2015 02:54 PM, Baoquan He wrote:
> >On 05/21/15 at 09:27am, Li, ZhenHua wrote:
> >>Hi Baoquan,
> >>
> >>In the early version of this patchset, old page tables are used by new
> >>kernel.  But as discussed, we need to make kernel use new pages when
> >>there is a new dma request , so we need to unmap the pages which were
> >>mapped in old kernel, and this is what this patch does.
> >
> >OK, just a new page table allocated in init_domain(), right? I thought a
> >specific empty page-table is allocated for these new domains in kdump
> >kernel.
> >
> >>
> >>Thanks
> >>Zhenhua
> >>
> >>On 05/21/2015 07:52 AM, Baoquan He wrote:
> >>>On 05/11/15 at 05:52pm, Li, Zhen-Hua wrote:
> >>>>When a device driver issues the first dma_map command for a device, we
> >>>>assign a new and empty page-table, thus removing all mappings from the
> >>>>old kernel for the device.
> >>>
> >>>Hi Zhenhua,
> >>>
> >>> From your patch I got it will remove all mappings, assign a new
> >>>page-table. But I didn't got why you stress an empty page-table. Did I
> >>>miss anything?
> >>>
> >>>Thanks
> >>>Baoquan
> >>>
> >>>>
> >>>>Signed-off-by: Li, Zhen-Hua <zhen-hual@...com>
> >>>>--
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