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From: Mathieu Desnoyers <mathieu.desnoyers-vg+e7yoeK/dWk0Htik3J/w@public.gmane.org>
Subject: Re: [RFC PATCH v3 for 4.15 08/24] Provide cpu_opv system call
Date: Mon, 20 Nov 2017 18:42:00 +0000 (UTC)
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To: Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>
Cc: Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>, "Paul E. McKenney" <paulmck-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>, Boqun Feng <boqun.feng-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org>, Dave Watson <davejwatson-b10kYP2dOMg@public.gmane.org>, linux-kernel <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, linux-api <linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Paul Turner <pjt-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, Russell King <linux-lFZ/pmaqli7XmaaqVzeoHQ@public.gmane.org>, Ingo Molnar <mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, "H. Peter Anvin" <hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org>, Andrew Hunter <ahh-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Andi Kleen <andi-Vw/NltI1exuRpAAqCnN02g@public.gmane.org>, Chris Lameter <cl-vYTEC60ixJUAvxtiuMwx3w@public.gmane.org>, Ben Maurer <bmaurer-b10kYP2dOMg@public.gmane.org>, rostedt <rostedt-nx8X9YLhiw1AfugRpC6u6w@public.gmane.org>, Josh Triplett <josh-iaAMLnmF4UmaiuxdJuQwMA@public.gmane.org>, Linus Torvalds <torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, Catalin Marinas <catalin.marinas-5wv7dgnIgG8@public.gmane.org>, Will Deacon <wil>
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----- On Nov 20, 2017, at 1:03 PM, Thomas Gleixner tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org wrote:

> On Mon, 20 Nov 2017, Thomas Gleixner wrote:
>> On Mon, 20 Nov 2017, Mathieu Desnoyers wrote:
>> > >> + * The reason why we require all pointer offsets to be calculated by
>> > >> + * user-space beforehand is because we need to use get_user_pages_fast()
>> > >> + * to first pin all pages touched by each operation. This takes care of
>> > > 
>> > > That doesnt explain it either.
>> > 
>> > What kind of explication are you looking for here ? Perhaps being too close
>> > to the implementation prevents me from understanding what is unclear from
>> > your perspective.
>> 
>> What the heck are pointer offsets?
>> 
>> The ops have one or two pointer(s) to a lump of memory. So if a pointer
>> points to the wrong lump of memory then you're screwed, but that's true for
>> all pointers handed to the kernel.
> 
> So I think you mix here the 'user space programmer guide - how to set up
> the magic ops - into the kernel side documentation. The kernel side does
> not care about the pointers, as long as they are valid to access.
> 
> Again. Try to explain things at the conceptual level.

Yes, I took the sentence you suggested for that reason: it removes
usage details that are meant for user-space implementer, which do not
belong in those comments.

Thanks,

Mathieu

> 
> Thanks,
> 
> 	tglx

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com