linux-kernel - Re: Using ion memory for direct-io

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Date:   Mon, 17 Apr 2017 09:13:48 -0700
From:   Laura Abbott <labbott@...hat.com>
To:     "Zengtao (B)" <prime.zeng@...ilicon.com>,
        "sumit.semwal@...aro.org" <sumit.semwal@...aro.org>
Cc:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "arve@...roid.com" <arve@...roid.com>,
        "riandrews@...roid.com" <riandrews@...roid.com>,
        "devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Using ion memory for direct-io

On 04/14/2017 02:18 AM, Zengtao (B) wrote:
> Hi 
> 
> Currently, the ion mapped to userspace will be forced with VM_IO and VM_PFNMAP flags.
> When I use the ion memory to do the direct-io, it will fail when reaching the get_user_pages,
> 
> Back to the VM_IO and VM_PFNMAP flag, there two flags are introduced by the remap_pfn_range called 
> by the ion_heap_mmap_user.
> 
> From my point of view, all ion memory(cma/vmalloc/system heap) are managed by linux vm, it
> is not reasonable to have the VM_IO and VM_PFNMAP flag, but I don't any suitable function
> to replace the remap_pfn_range, any suggestions?
> 
> Thanks && Regards
> 
> Zengtao 
> 

The carveout heap is omitted from your list of 'all ion memory'. At one
time, carveout memory was not backed by struct pages so I suspect
this is a holdover from then. This would probably be better served
by using vm_insert_page and handling higher order pages properly.

Thanks,
Laura