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Re: [PATCH 2/3] x86: add some better documentation for probe_kernel_address()

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On Fri, Jul 22, 2016 at 11:18 AM, Dave Hansen <dave@sr71.net> wrote:
> On 07/22/2016 11:10 AM, Andy Lutomirski wrote:
>> On Jul 22, 2016 11:03 AM, "Dave Hansen" <dave@sr71.net> wrote:
>>> From: Dave Hansen <dave.hansen@linux.intel.com>
>>>
>>> probe_kernel_address() has an unfortunate name since it is used
>>> to probe kernel *and* userspace addresses.  Add a comment
>>> explaining some of the situation to help the next developer who
>>> might make the silly assumption that it is for probing kernel
>>> addresses.
>>
>> This can't work on architectures like s390 that have separate,
>> overlapping user and kernel address spaces.  Maybe we should fix x86
>> to stop abusing it and use get_user instead.  (In which case, your new
>> function should be called get_user_insn_byte or similar.)
>
> Urg.
>
> But can't the x86 use in no_context() be called from a kernel-initiated
> fault?  Like a prefetch instruction to a vmalloc() page that we needed
> to do a vmalloc fault for?
>
> In either case, it would be awfully nice to have the clarity about
> exactly what is being probed.  The other 2 calls to is_prefetch() do
> appear to be userspace-only.

Indeed.

Perhaps we should pass a bool is_kernel into is_prefetch().

--Andy

-- 
Andy Lutomirski
AMA Capital Management, LLC

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[PATCH 0/3] x86, pkeys: fix prefetch/pkeys interaction Dave Hansen <dave@sr71.net> - 2016-07-22 20:10 +0200
  [PATCH 2/3] x86: add some better documentation for probe_kernel_address() Dave Hansen <dave@sr71.net> - 2016-07-22 20:10 +0200
    Re: [PATCH 2/3] x86: add some better documentation for probe_kernel_address() Andy Lutomirski <luto@amacapital.net> - 2016-07-22 20:20 +0200
      Re: [PATCH 2/3] x86: add some better documentation for  probe_kernel_address() Dave Hansen <dave@sr71.net> - 2016-07-22 20:20 +0200
        Re: [PATCH 2/3] x86: add some better documentation for probe_kernel_address() Andy Lutomirski <luto@amacapital.net> - 2016-07-22 20:30 +0200
  [PATCH 3/3] x86, pkeys: allow instruction fetches in presence of pkeys Dave Hansen <dave@sr71.net> - 2016-07-22 20:10 +0200

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