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Re: [PATCH] Implement protection key support for POWER

On 05/23/2018 12:59 PM, Florian Weimer wrote:
> On 05/23/2018 06:44 PM, Carlos O'Donell wrote:
>> That makes perfect sense, thanks for explaining that. So on pre-ISA3.0
>> hardware you can't get a value from pkey_alloc() because the kernel
>> would handle that side of the equation.
> Ahem.  I already said that this has nothing to do with ISA 3.0.  The feature is available on the Fedora builders, for example, which are not ISA 3.0.

My apologies, let me explain in more detail.

I thought userspace AMR access was added on ISA v3.0.

AMR access in userspace was added in ISA v2.06 Rev B
(via the non-privileged SPR number used in your implementation).

I expect the kernel pkey_alloc() syscall to fail on hardware that
does not support the Authority Mask Register, or some fallback

In Fedora we support quite old POWER hardware, therefore on these
systems the above pkey_alloc() will fail and we won't use this
feature, and will never call any of the functions you add which
might be using a reserved/undefined SPR number on that old hardware.

Does that clarify the point I wanted to make?

>> Are we interested in adding this support right know given the bugs
>> and potential future changes?
> Yes, I think even with the current set of kernel bugs, the whole
> thing is still good enough for protecting the GOT and flip access
> rights in _dl_fixup.
Your patch looks good to me then.


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