From: Sebastian Frias <sebastian_frias@sigmadesigns.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Marc Gonzalez <marc_gonzalez@sigmadesigns.com>,
linux-mm <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: m(un)map kmalloc buffers to userspace
Date: Wed, 9 Dec 2015 16:35:53 +0100 [thread overview]
Message-ID: <56684A59.7030605@sigmadesigns.com> (raw)
In-Reply-To: <20151209151254.GH30907@dhcp22.suse.cz>
On 12/09/2015 04:12 PM, Michal Hocko wrote:
> On Wed 09-12-15 15:53:22, Sebastian Frias wrote:
> [...]
>> 2) Now that VM_RESERVED was removed, is there another recommended flag to
>> replace it for the purposes above?
>
> VM_IO + potentially others depending on your usecase.
>
>> 3) Since it was working before, we suppose that something that was
>> previously done by default on the kernel it is not done anymore, could that
>> be a remap_pfn_range during mmap or kmalloc?
>
> VM_RESERVED removal was a cleanup which has removed the flag because it
> was not needed and the same effect could be implied from either VM_IO or
> VM_DONTEXPAND | VM_DONTDUMP. See 314e51b9851b ("mm: kill vma flag
> VM_RESERVED and mm->reserved_vm counter") for more detailed information.
>
>> 4) We tried using remap_pfn_range inside mmap and while it seems to work, we
>> still get occasional crashes due to corrupted memory (in this case the
>> behaviour is the same between 4.1 and 3.4 when using the same modified
>> driver), are we missing something?
>
> This is hard to tell without knowing your driver. I would just encourage
> you to look at other drivers which map kernel memory to userspace via
> mmap. There are many of them. Maybe you can find a pattern which suites
> your usecase.
>
Ok, thanks.
We've seen that drivers/media/pci/zoran/zoran_driver.c for example seems
to be doing as us kmalloc+remap_pfn_range, is there any guarantee (or at
least an advised heuristic) to determine if a driver is "current" (ie:
uses the latest APIs and works)?
next prev parent reply other threads:[~2015-12-09 15:35 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-08 17:25 m(un)map kmalloc buffers to userspace Sebastian Frias
2015-12-09 13:55 ` Michal Hocko
2015-12-09 14:07 ` Marc Gonzalez
2015-12-09 14:32 ` Michal Hocko
2015-12-09 14:53 ` Sebastian Frias
2015-12-09 15:12 ` Michal Hocko
2015-12-09 15:35 ` Sebastian Frias [this message]
2015-12-10 11:40 ` Michal Hocko
2015-12-10 12:04 ` Richard Weinberger
2015-12-10 13:37 ` Sebastian Frias
2015-12-10 14:06 ` Michal Hocko
2015-12-10 16:48 ` Sebastian Frias
2015-12-11 9:42 ` Michal Hocko
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