Re: Map memory to user, then map it back to kernel

From: Jiri Slaby
Date: Wed Aug 09 2006 - 10:30:07 EST

sasha wrote:
Hi folks.

I am looking for a way to map a memory (allocated with get_free_pages()) from kernel space to user space, so that I will later be able to map it back with get_user_pages().

I tried remap_pfn_range(), but it didn't work as it assumes the memory being mapped is IO range (marking vma with VM_IO flag), while get_user_pages() works on regular memory.

Any ideas?

VM_IO flag means not to swap this memory and don't do any side-effects bound with that IIRC.

If you want to mmap some memory in kernel to allow userspace to be able to read from it, just remap and don't care. I actually don't understand, what you mean by remapping it back to kernelspace, can you be more specific?

Caveat of get_free_pages is that it allocates physically contiguous memory and this may fail in later times, when the memory is not so free. You can use virtual memory to avoid this: vmalloc_32_user, remap_vmalloc_range, vfree.

<a href="";>Jiri Slaby</a>
faculty of informatics, masaryk university, brno, cz
e-mail: jirislaby gmail com, gpg pubkey fingerprint:
B674 9967 0407 CE62 ACC8 22A0 32CC 55C3 39D4 7A7E
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at