Re: [Qemu-devel] [PATCH 0/4] madvise(MADV_USERFAULT) & sys_remap_anon_pages()

[Andrew Jones <drjones@redhat.com>]

On Mon, May 06, 2013 at 09:56:57PM +0200, Andrea Arcangeli wrote:
> 
> The current behavior of remap_anon_pages is very strict to avoid any
> chance of memory corruption going unnoticed, and it will return
> -EFAULT at the first sign of something unexpected (like a page already
> mapped in the destination pmd/pte, potentially signaling an userland
> thread race condition with two threads userfaulting on the same
> destination address). mremap is not strict like that: it would drop
> the destination range silently and it would succeed in such a
> condition. So on the API side, I wonder if I should add a flag to
> remap_anon_pages to provide non-strict behavior more similar to
> mremap. OTOH not providing the permissive mremap behavior may actually
> be better to force userland to be strict and be sure it knows what it
> is doing (otherwise it should use mremap in the first place?).
> 

What about instead of adding a new syscall (remap_anon_pages) to
instead extend mremap with new flags giving it a strict mode?

drew