Re: m(un)map kmalloc buffers to userspace

[Michal Hocko <mhocko@kernel.org>]

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.

-- 
Michal Hocko
SUSE Labs

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>