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Message-ID: <20170811162605.tr4tig4av3q4fll6@hirez.programming.kicks-ass.net>
Date: Fri, 11 Aug 2017 18:26:05 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Jork Loeser <Jork.Loeser@...rosoft.com>,
KY Srinivasan <kys@...rosoft.com>,
Simon Xiao <sixiao@...rosoft.com>,
Haiyang Zhang <haiyangz@...rosoft.com>,
Stephen Hemminger <sthemmin@...rosoft.com>,
"luto@...nel.org" <luto@...nel.org>,
"hpa@...or.com" <hpa@...or.com>,
"vkuznets@...hat.com" <vkuznets@...hat.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"rostedt@...dmis.org" <rostedt@...dmis.org>,
"andy.shevchenko@...il.com" <andy.shevchenko@...il.com>,
"tglx@...utronix.de" <tglx@...utronix.de>,
"mingo@...nel.org" <mingo@...nel.org>,
"linux-tip-commits@...r.kernel.org"
<linux-tip-commits@...r.kernel.org>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [tip:x86/platform] x86/hyper-v: Use hypercall for remote TLB
flush
On Fri, Aug 11, 2017 at 09:16:29AM -0700, Linus Torvalds wrote:
> On Fri, Aug 11, 2017 at 2:03 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> >
> > I'm sure we talked about using HAVE_RCU_TABLE_FREE for x86 (and yes that
> > would make it work again), but this was some years ago and I cannot
> > readily find those emails.
>
> I think the only time we really talked about HAVE_RCU_TABLE_FREE for
> x86 (at least that I was cc'd on) was not because of RCU freeing, but
> because we just wanted to use the generic page table lookup code on
> x86 *despite* not using RCU freeing.
>
> And we just ended up renaming HAVE_GENERIC_RCU_GUP as HAVE_GENERIC_GUP.
>
> There was only passing mention of maybe making x86 use RCU, but the
> discussion was really about why the IF flag meant that x86 didn't need
> to, iirc.
>
> I don't recall us ever discussing *really* making x86 use RCU.
Google finds me this:
https://lwn.net/Articles/500188/
Which includes:
http://www.mail-archive.com/kvm@vger.kernel.org/msg72918.html
which does as was suggested here, selects HAVE_RCU_TABLE_FREE for
PARAVIRT_TLB_FLUSH.
But yes, this is very much virt specific nonsense, native would never
need this.
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