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 16:40:11 +0800
From:	"Li, ZhenHua" <zhen-hual@...com>
To:	Baoquan He <bhe@...hat.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, "Li, ZhenHua" <zhen-hual@...com>
Subject: Re: [PATCH v11 08/10] iommu/vt-d: assign new page table for dma_map

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.

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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