Date: Wed, 1 Oct 2003 00:55:28 +0100
From: Jamie Lokier <jamie@shareable.org>
To: Dave Jones <davej@redhat.com>, akpm@osdl.org, torvalds@osdl.org,
       linux-kernel@vger.kernel.org, richard.brunner@amd.com
Subject: Re: [PATCH] Mutilated form of Andi Kleen's AMD prefetch errata patch
Message-ID: <20030930235528.GA32209@mail.shareable.org>
References: <20030930073814.GA26649@mail.jlokier.co.uk> <20030930132211.GA23333@redhat.com> <20030930133936.GA28876@mail.shareable.org> <20030930135324.GC5507@redhat.com> <20030930144526.GC28876@mail.shareable.org> <20030930150825.GD5507@redhat.com> <20030930165450.GF28876@mail.shareable.org> <20030930172618.GE5507@redhat.com>
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Dave Jones wrote:
> Which gets us back to the question of why this is needed at all ?
> You said earlier "In case you hadn't fully grokked it, my code doesn't
> disable the workaround!"  So why do you need this ?

To change the prefetch workaround from a critical requirement to an
optimisation knob.

X86_USE_3DNOW is very similar: if it's enabled, the kernel has some
extra code to make certain CPUs run faster, but they also run fine
without it.  X86_OOSTORE is another.

What I'd really like your opinion on is the appropriate userspace
behaviour.  If we don't care about fixing up userspace, then
__ex_table is a much tidier workaround for the prefetch bug.  If we do
care about fixing up userspace, then do we need a policy decision that
says it's not acceptable to run on AMD without userspace fixups from
2.6.0 onwards - it must fixup userspace or refuse to run?

-- Jamie
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