linux-kernel - Re: [PATCH 4/6] powerpc/64s: Enable barrier

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Date:   Tue, 01 May 2018 21:11:06 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Michal Suchánek <msuchanek@...e.de>
Cc:     linuxppc-dev@...abs.org, linux-kernel@...r.kernel.org,
        npiggin@...il.com
Subject: Re: [PATCH 4/6] powerpc/64s: Enable barrier_nospec based on firmware settings

Michal Suchánek <msuchanek@...e.de> writes:
> Hello,
>
> On Tue, 24 Apr 2018 14:15:57 +1000
> Michael Ellerman <mpe@...erman.id.au> wrote:
>
>> From: Michal Suchanek <msuchanek@...e.de>
>> 
>> Check what firmware told us and enable/disable the barrier_nospec as
>> appropriate.
>> 
>> We err on the side of enabling the barrier, as it's no-op on older
>> systems, see the comment for more detail.
>> 
>> Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
...
>
> I am missing the option for the barrier to be disabled by a kernel
> commandline argument here.
>
> It does make sense to add a kernel parameter that is checked on boot to
> be compatible with other platforms that implement one.

No other platforms have an option to disable variant 1 mitigations, so
there isn't an existing parameter we can use.

Which is not to say we can't add one, but I wasn't sure if it was really
worth it.

But I guess we should add one, I might do it as a follow-up patch.

cheers