Messages in this thread | | | Date | Wed, 9 Dec 2015 16:12:55 +0100 | From | Michal Hocko <> | Subject | Re: m(un)map kmalloc buffers to userspace |
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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
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