Messages in this thread | | | Date | Fri, 10 Apr 2015 10:49:21 -0700 | Subject | Re: [PATCH] x86/uaccess: Implement get_kernel() | From | Linus Torvalds <> |
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On Fri, Apr 10, 2015 at 4:14 AM, Ingo Molnar <mingo@kernel.org> wrote: > >> >> The next patch will implement efficient __copy_from_kernel_inatomic() >> for x86. > > The patch below does that. Note, for simplicity I've changed the > interface to 'get_kernel()' (will propagate this through the other > patches as well).
So I think this needs a couple of changes:
- That "get_kernel()" name is not clear enough about what the issue is. I think it should make it clearer that it's an unsafe access that could fault, and that we don't want a user access.
So maybe "get_kernel_stalepointer()" or something like that.
- you're just re-implementing "__get_user_asm_ex()" afaik. Try to share the code, renaming it to be something common.
- I think we should look at sharing the code for __get_user(). Could we do something like this:
(a) implement the basic "load with exceptions" as __get_with_exception() (b) #define get_kernel_stalepointer() __get_with_exception (c) make "__get_user()" be "stac(); __get_with_exception(); clac()"
- finally, I wonder what the exact semantics of "get_kernel_stalepointer()" should be. I could well imagine that what we should do is
#ifdef CONFIG_DEBUG_PAGEALLOC #define get_kernel_stalepointer(x,ptr) ((x)=READ_ONCE(*(ptr)), 0) #else #define get_kernel_stalepointer(x,ptr) __get_with_exception(x,ptr) #endif
because I think it's reasonable to require that the kernel pointer is _stale_, and not "invalid". IOW, guarantee that it *has* been a kernel pointer, and that the only reason it would trap is for DEBUG_PAGEALLOC.
That last point might need to be verified with hotplug memory. I think hotplug memory does a stop_machine() or similar, but I'm not sure.
Hmm?
Linus
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