Re: use exact allocation for dma coherent memory

Re: use exact allocation for dma coherent memory

[Jason Gunthorpe]

On Mon, Jun 17, 2019 at 10:33:42AM +0200, Christoph Hellwig wrote:
> > drivers/infiniband/hw/cxgb4/qp.c
> >    129  static int alloc_host_sq(struct c4iw_rdev *rdev, struct t4_sq *sq)
> >    130  {
> >    131          sq->queue = dma_alloc_coherent(&(rdev->lldi.pdev->dev), sq->memsize,
> >    132                                         &(sq->dma_addr), GFP_KERNEL);
> >    133          if (!sq->queue)
> >    134                  return -ENOMEM;
> >    135          sq->phys_addr = virt_to_phys(sq->queue);
> >    136          dma_unmap_addr_set(sq, mapping, sq->dma_addr);
> >    137          return 0;
> >    138  }
> > 
> > Is this a bug?
> 
> Yes.  This will blow up badly on many platforms, as sq->queue
> might be vmapped, ioremapped, come from a pool without page backing.

Gah, this addr gets fed into io_remap_pfn_range/remap_pfn_range too..

Potnuri, you should fix this.. 

You probably need to use dma_mmap_from_dev_coherent() in the mmap ?

Jason
_______________________________________________
devel mailing list
devel@linuxdriverproject.org
http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel

Re: use exact allocation for dma coherent memory

[Christoph Hellwig]

On Wed, Jun 19, 2019 at 01:29:03PM -0300, Jason Gunthorpe wrote:
> > Yes.  This will blow up badly on many platforms, as sq->queue
> > might be vmapped, ioremapped, come from a pool without page backing.
> 
> Gah, this addr gets fed into io_remap_pfn_range/remap_pfn_range too..
> 
> Potnuri, you should fix this.. 
> 
> You probably need to use dma_mmap_from_dev_coherent() in the mmap ?

The function to use is dma_mmap_coherent, dma_mmap_from_dev_coherent is
just an internal helper.

That beiŋ said the drivers/infiniband code has a lot of
*remap_pfn_range, and a lot of them look like they might be for
DMA memory.
_______________________________________________
devel mailing list
devel@linuxdriverproject.org
http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel

Re: use exact allocation for dma coherent memory

[Christoph Hellwig]

On Fri, Jun 14, 2019 at 03:47:10PM +0200, Christoph Hellwig wrote:
> Switching to a slightly cleaned up alloc_pages_exact is pretty easy,
> but it turns out that because we didn't filter valid gfp_t flags
> on the DMA allocator, a bunch of drivers were passing __GFP_COMP
> to it, which is rather bogus in too many ways to explain.  Arm has
> been filtering it for a while, but this series instead tries to fix
> the drivers and warn when __GFP_COMP is passed, which makes it much
> larger than just adding the functionality.

Dear driver maintainers,

can you look over the patches touching your drivers, please?  I'd
like to get as much as possible of the driver patches into this
merge window, so that it can you through your maintainer trees.
_______________________________________________
devel mailing list
devel@linuxdriverproject.org
http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel

Re: use exact allocation for dma coherent memory

[Arend Van Spriel]

On 7/1/2019 10:48 AM, Christoph Hellwig wrote:
> On Fri, Jun 14, 2019 at 03:47:10PM +0200, Christoph Hellwig wrote:
>> Switching to a slightly cleaned up alloc_pages_exact is pretty easy,
>> but it turns out that because we didn't filter valid gfp_t flags
>> on the DMA allocator, a bunch of drivers were passing __GFP_COMP
>> to it, which is rather bogus in too many ways to explain.  Arm has
>> been filtering it for a while, but this series instead tries to fix
>> the drivers and warn when __GFP_COMP is passed, which makes it much
>> larger than just adding the functionality.
> 
> Dear driver maintainers,
> 
> can you look over the patches touching your drivers, please?  I'd
> like to get as much as possible of the driver patches into this
> merge window, so that it can you through your maintainer trees.

You made me look ;-) Actually not touching my drivers so I'm off the 
hook. However, I was wondering if drivers could know so I decided to 
look into the DMA-API.txt documentation which currently states:

"""
The flag parameter (dma_alloc_coherent() only) allows the caller to
specify the ``GFP_`` flags (see kmalloc()) for the allocation (the
implementation may choose to ignore flags that affect the location of
the returned memory, like GFP_DMA).
"""

I do expect you are going to change that description as well now that 
you are going to issue a warning on __GFP_COMP. Maybe include that in 
patch 15/16 where you introduce that warning.

Regards,
Arend
_______________________________________________
devel mailing list
devel@linuxdriverproject.org
http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel

Re: use exact allocation for dma coherent memory

[Christoph Hellwig]

On Tue, Jul 02, 2019 at 11:48:44AM +0200, Arend Van Spriel wrote:
> You made me look ;-) Actually not touching my drivers so I'm off the hook. 
> However, I was wondering if drivers could know so I decided to look into 
> the DMA-API.txt documentation which currently states:
>
> """
> The flag parameter (dma_alloc_coherent() only) allows the caller to
> specify the ``GFP_`` flags (see kmalloc()) for the allocation (the
> implementation may choose to ignore flags that affect the location of
> the returned memory, like GFP_DMA).
> """
>
> I do expect you are going to change that description as well now that you 
> are going to issue a warning on __GFP_COMP. Maybe include that in patch 
> 15/16 where you introduce that warning.

Yes, that description needs an updated, even without this series.
I'll make sure it is more clear.
_______________________________________________
devel mailing list
devel@linuxdriverproject.org
http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel