Subject: Re: [PATCH] powerpc/mm: Allow user space to map rtas_rmo_buf

From: Vasant Hegde <[email-masked]>
Date: Fri, 22 Jan 2016 11:58:44 +0530

On 01/22/2016 10:59 AM, Michael Ellerman wrote:
> On Thu, 2016-01-21 at 21:45 +0530, Vasant Hegde wrote:
> 
>> With commit 90a545e9 (restrict /dev/mem to idle io memory ranges) mapping
>> rtas_rmo_buf from user space is failing. Hence we are not able to make
>> RTAS syscall.
>>
>> This patch calls page_is_rtas_user_buf before calling iomem_is_exclusive
>> in  devmem_is_allowed(). This will allow user space to map rtas_rmo_buf
>> and we are able to make RTAS syscall.

Michael,

> 
> Thanks for the patch.
> 
> I'll put it in my fixes branch for next week.

Thanks!

> 
> 
> Having said that, why the <expletive deleted> is librtas mapping /dev/mem in
> the first place? Unless there is a very good reason, and probably even if there
> is, we should fix that to use a sane API.

We use rtas system call. We use /dev/mem interface to map the RTAS memory region
(allocated by kernel and information is passed to user space via procfs) so that
we can read/write to RTAS memory.

I do not have historical information. May be Nathan has more information on this.

-Vasant