linux-kernel - Re: [PATCH v1 4/9] iommu/vt-d: Add bounce buffer API for domain map/unmap

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Date:   Tue, 19 Mar 2019 15:59:48 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     baolu.lu@...ux.intel.com, David Woodhouse <dwmw2@...radead.org>,
        Joerg Roedel <joro@...tes.org>, ashok.raj@...el.com,
        jacob.jun.pan@...el.com, alan.cox@...el.com, kevin.tian@...el.com,
        mika.westerberg@...ux.intel.com, pengfei.xu@...el.com,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>
Subject: Re: [PATCH v1 4/9] iommu/vt-d: Add bounce buffer API for domain
 map/unmap

Hi Christoph,

On 3/14/19 12:10 AM, Christoph Hellwig wrote:
> On Wed, Mar 13, 2019 at 10:31:52AM +0800, Lu Baolu wrote:
>> Hi again,
>>
>> On 3/13/19 10:04 AM, Lu Baolu wrote:
>>> Hi,
>>>
>>> On 3/13/19 12:38 AM, Christoph Hellwig wrote:
>>>> On Tue, Mar 12, 2019 at 02:00:00PM +0800, Lu Baolu wrote:
>>>>> This adds the APIs for bounce buffer specified domain
>>>>> map() and unmap(). The start and end partial pages will
>>>>> be mapped with bounce buffered pages instead. This will
>>>>> enhance the security of DMA buffer by isolating the DMA
>>>>> attacks from malicious devices.
>>>>
>>>> Please reuse the swiotlb code instead of reinventing it.
>>>>
>>
>> Just looked into the code again. At least we could reuse below
>> functions:
>>
>> swiotlb_tbl_map_single()
>> swiotlb_tbl_unmap_single()
>> swiotlb_tbl_sync_single()
>>
>> Anything else?
> 
> Yes, that is probably about the level you want to reuse, given that the
> next higher layer already has hooks into the direct mapping code.
> 

I am trying to change my code to reuse swiotlb. But I found that swiotlb
might not be suitable for my case.

Below is what I got with swiotlb_map():

phy_addr        size    tlb_addr
--------------------------------
0x167eec330     0x8     0x85dc6000
0x167eef5c0     0x40    0x85dc6800
0x167eec330     0x8     0x85dc7000
0x167eef5c0     0x40    0x85dc7800

But what I expected to get is:

phy_addr        size    tlb_addr
--------------------------------
0x167eec330     0x8     0xAAAAA330
0x167eef5c0     0x40    0xBBBBB5c0
0x167eec330     0x8     0xCCCCC330
0x167eef5c0     0x40    0xDDDDD5c0

, where 0xXXXXXX000 is the physical address of a bounced page.

Basically, I want a bounce page to replace a leaf page in the vt-d page
table, which maps a buffer with size less than a PAGE_SIZE.

Best regards,
Lu Baolu