Linux-Next Archive on lore.kernel.org
 help / color / Atom feed
From: Minchan Kim <minchan@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Nadav Amit <namit@vmware.com>, Ingo Molnar <mingo@kernel.org>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	Andrew Morton <akpm@linux-foundation.org>,
	Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Linux-Next Mailing List <linux-next@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linus <torvalds@linux-foundation.org>
Subject: Re: linux-next: manual merge of the akpm-current tree with the tip tree
Date: Mon, 14 Aug 2017 12:16:13 +0900
Message-ID: <20170814031613.GD25427@bbox> (raw)
In-Reply-To: <20170813125019.ihqjud37ytgri7bn@hirez.programming.kicks-ass.net>

On Sun, Aug 13, 2017 at 02:50:19PM +0200, Peter Zijlstra wrote:
> On Sun, Aug 13, 2017 at 06:06:32AM +0000, Nadav Amit wrote:
> > > however mm_tlb_flush_nested() is a mystery, it appears to care about
> > > anything inside the range. For now rely on it doing at least _a_ PTL
> > > lock instead of taking  _the_ PTL lock.
> > 
> > It does not care about “anything” inside the range, but only on situations
> > in which there is at least one (same) PT that was modified by one core and
> > then read by the other. So, yes, it will always be _the_ same PTL, and not
> > _a_ PTL - in the cases that flush is really needed.
> > 
> > The issue that might require additional barriers is that
> > inc_tlb_flush_pending() and mm_tlb_flush_nested() are called when the PTL is
> > not held. IIUC, since the release-acquire might not behave as a full memory
> > barrier, this requires an explicit memory barrier.
> 
> So I'm not entirely clear about this yet.
> 
> How about:
> 
> 
> 	CPU0				CPU1
> 
> 					tlb_gather_mmu()
> 
> 					lock PTLn
> 					no mod
> 					unlock PTLn
> 
> 	tlb_gather_mmu()
> 
> 					lock PTLm
> 					mod
> 					include in tlb range
> 					unlock PTLm
> 
> 	lock PTLn
> 	mod
> 	unlock PTLn
> 
> 					tlb_finish_mmu()
> 					  force = mm_tlb_flush_nested(tlb->mm);
> 					  arch_tlb_finish_mmu(force);
> 
> 
> 	... more ...
> 
> 	tlb_finish_mmu()
> 
> 
> 
> In this case you also want CPU1's mm_tlb_flush_nested() call to return
> true, right?

No, because CPU 1 mofified pte and added it into tlb range
so regardless of nested, it will flush TLB so there is no stale
TLB problem.

> 
> But even with an smp_mb__after_atomic() at CPU0's tlg_bather_mmu()
> you're not guaranteed CPU1 sees the increment. The only way to do that
> is to make the PTL locks RCsc and that is a much more expensive
> proposition.
> 
> 
> What about:
> 
> 
> 	CPU0				CPU1
> 
> 					tlb_gather_mmu()
> 
> 					lock PTLn
> 					no mod
> 					unlock PTLn
> 
> 
> 					lock PTLm
> 					mod
> 					include in tlb range
> 					unlock PTLm
> 
> 	tlb_gather_mmu()
> 
> 	lock PTLn
> 	mod
> 	unlock PTLn
> 
> 					tlb_finish_mmu()
> 					  force = mm_tlb_flush_nested(tlb->mm);
> 					  arch_tlb_finish_mmu(force);
> 
> 
> 	... more ...
> 
> 	tlb_finish_mmu()
> 
> Do we want CPU1 to see it here? If so, where does it end?

Ditto. Since CPU 1 has added range, it will flush TLB regardless
of nested condition.

> 
> 	CPU0				CPU1
> 
> 					tlb_gather_mmu()
> 
> 					lock PTLn
> 					no mod
> 					unlock PTLn
> 
> 
> 					lock PTLm
> 					mod
> 					include in tlb range
> 					unlock PTLm
> 
> 					tlb_finish_mmu()
> 					  force = mm_tlb_flush_nested(tlb->mm);
> 
> 	tlb_gather_mmu()
> 
> 	lock PTLn
> 	mod
> 	unlock PTLn
> 
> 					  arch_tlb_finish_mmu(force);
> 
> 
> 	... more ...
> 
> 	tlb_finish_mmu()
> 
> 
> This?
> 
> 
> Could you clarify under what exact condition mm_tlb_flush_nested() must
> return true?

mm_tlb_flush_nested aims for the CPU side where there is no pte update
but need TLB flush.
As I wrote https://marc.info/?l=linux-mm&m=150267398226529&w=2,
it has stable TLB problem if we don't flush TLB although there is no
pte modification.

  reply index

Thread overview: 87+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-11  7:53 Stephen Rothwell
2017-08-11  9:34 ` Peter Zijlstra
2017-08-11 10:48   ` Peter Zijlstra
2017-08-11 11:45   ` Stephen Rothwell
2017-08-11 11:56     ` Ingo Molnar
2017-08-11 12:17       ` Peter Zijlstra
2017-08-11 12:44         ` Ingo Molnar
2017-08-11 13:49           ` Stephen Rothwell
2017-08-11 14:04       ` Peter Zijlstra
2017-08-13  6:06         ` Nadav Amit
2017-08-13 12:50           ` Peter Zijlstra
2017-08-14  3:16             ` Minchan Kim [this message]
2017-08-14  5:07               ` Nadav Amit
2017-08-14  5:23                 ` Minchan Kim
2017-08-14  8:38                 ` Minchan Kim
2017-08-14 19:57                   ` Peter Zijlstra
2017-08-16  4:14                     ` Minchan Kim
2017-08-14 19:38                 ` Peter Zijlstra
2017-08-15  7:51                   ` Nadav Amit
2017-08-14  3:09         ` Minchan Kim
2017-08-14 18:54           ` Peter Zijlstra
  -- strict thread matches above, loose matches on Subject: below --
2019-10-31  5:43 Stephen Rothwell
2019-06-24 10:24 Stephen Rothwell
2019-05-01 11:10 Stephen Rothwell
2019-01-31  4:31 Stephen Rothwell
2018-08-20  4:32 Stephen Rothwell
2018-08-20 19:52 ` Andrew Morton
2018-03-23  5:59 Stephen Rothwell
2017-12-18  5:04 Stephen Rothwell
2017-11-10  4:33 Stephen Rothwell
2017-11-02  7:19 Stephen Rothwell
2017-08-22  6:57 Stephen Rothwell
2017-08-23  6:39 ` Vlastimil Babka
2017-04-12  6:46 Stephen Rothwell
2017-04-12 20:53 ` Vlastimil Babka
2017-04-20  2:17   ` NeilBrown
2017-03-24  5:25 Stephen Rothwell
2017-02-17  4:40 Stephen Rothwell
2016-11-14  6:08 Stephen Rothwell
2016-07-29  4:14 Stephen Rothwell
2016-06-15  5:23 Stephen Rothwell
2016-06-18 19:39 ` Manfred Spraul
2016-04-29  6:12 Stephen Rothwell
2016-04-29  6:26 ` Ingo Molnar
2016-03-02  5:40 Stephen Rothwell
2016-02-26  5:07 Stephen Rothwell
2016-02-26 21:35 ` Andrew Morton
2016-02-19  4:09 Stephen Rothwell
2016-02-19 15:26 ` Ard Biesheuvel
2015-12-07  8:06 Stephen Rothwell
2015-10-02  4:21 Stephen Rothwell
2015-07-28  6:00 Stephen Rothwell
2015-07-29 17:12 ` Andrea Arcangeli
2015-07-29 17:47   ` Andy Lutomirski
2015-07-29 18:46     ` Thomas Gleixner
2015-07-30 15:38       ` Andrea Arcangeli
2015-07-29 23:06   ` Stephen Rothwell
2015-07-29 23:07     ` Thomas Gleixner
2015-09-07 23:35   ` Stephen Rothwell
2015-09-08 18:11     ` Linus Torvalds
2015-09-08 22:56       ` Stephen Rothwell
2015-09-08 23:03         ` Linus Torvalds
2015-09-08 23:21           ` Andrew Morton
2015-09-16  6:58             ` Geert Uytterhoeven
2015-06-04 12:07 Stephen Rothwell
2015-04-08  8:28 Stephen Rothwell
2015-04-08  8:25 Stephen Rothwell
2014-03-17  9:31 Stephen Rothwell
2014-03-17  9:36 ` Peter Zijlstra
2014-03-19 23:27   ` Andrew Morton
2014-01-14  4:53 Stephen Rothwell
2014-01-14  5:04 ` Davidlohr Bueso
2014-01-14 12:51 ` Peter Zijlstra
2014-01-14 13:17   ` Geert Uytterhoeven
2014-01-14 13:33     ` Peter Zijlstra
2014-01-14 16:19     ` H. Peter Anvin
2014-01-14 15:15   ` H. Peter Anvin
2014-01-14 15:20     ` Geert Uytterhoeven
2014-01-14 15:41       ` Peter Zijlstra
2014-01-14 15:48         ` H. Peter Anvin
2014-01-07  6:00 Stephen Rothwell
2014-01-07  6:34 ` Tang Chen
2013-11-08  7:48 Stephen Rothwell
2013-11-08 18:58 ` Josh Triplett
2013-11-08 23:20   ` Stephen Rothwell
2013-11-09  0:19     ` Josh Triplett
2013-10-30  6:40 Stephen Rothwell

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20170814031613.GD25427@bbox \
    --to=minchan@kernel.org \
    --cc=akpm@linux-foundation.org \
    --cc=hpa@zytor.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-next@vger.kernel.org \
    --cc=mingo@elte.hu \
    --cc=mingo@kernel.org \
    --cc=namit@vmware.com \
    --cc=peterz@infradead.org \
    --cc=sfr@canb.auug.org.au \
    --cc=tglx@linutronix.de \
    --cc=torvalds@linux-foundation.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-Next Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-next/0 linux-next/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-next linux-next/ https://lore.kernel.org/linux-next \
		linux-next@vger.kernel.org
	public-inbox-index linux-next

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-next


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git