Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i386,bisected, reproducable)

[Al Viro]

On Tue, Jun 17, 2008 at 02:24:39PM -0700, Linus Torvalds wrote:

> The whole *and*only* reason for copy_to/from_user() existing AT ALL is 
> exactly the fact that the source or destination access can fault. 

Erm...  The reason for copy_to_user() existing is that dereferencing
a user-supplied address in the kernel does not have to access any
memory reachable in user mode, regardless of any faults.  WTF are you
guys talking about?
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