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

[Lu Baolu]

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