From: Peter Zijlstra <peterz@infradead.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
linux-mm@kvack.org, Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@elte.hu>,
akpm@linux-foundation.org, Rik van Riel <riel@redhat.com>,
Hugh Dickins <hugh.dickins@tiscali.co.uk>,
Mel Gorman <mel@csn.ul.ie>, Nick Piggin <npiggin@kernel.dk>,
Alex Shi <alex.shi@intel.com>,
"Nikunj A. Dadhania" <nikunj@linux.vnet.ibm.com>,
Konrad Rzeszutek Wilk <konrad@darnok.org>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
David Miller <davem@davemloft.net>,
Russell King <rmk@arm.linux.org.uk>,
Catalin Marinas <catalin.marinas@arm.com>,
Chris Metcalf <cmetcalf@tilera.com>,
Martin Schwidefsky <schwidefsky@de.ibm.com>,
Tony Luck <tony.luck@intel.com>, Paul Mundt <lethal@linux-sh.org>,
Jeff Dike <jdike@addtoit.com>,
Richard Weinberger <richard@nod.at>,
Ralf Baechle <ralf@linux-mips.org>,
Kyle McMartin <kyle@mcmartin.ca>,
James Bottomley <jejb@parisc-linux.org>,
Chris Zankel <chris@zankel.net>
Subject: Re: [PATCH 08/20] mm: Optimize fullmm TLB flushing
Date: Thu, 28 Jun 2012 12:55:04 +0200 [thread overview]
Message-ID: <1340880904.28750.13.camel@twins> (raw)
In-Reply-To: <CA+55aFzLNsVRkp_US8rAmygEkQpp1s1YdakV86Ck-4RZM7TTdA@mail.gmail.com>
On Wed, 2012-06-27 at 16:33 -0700, Linus Torvalds wrote:
> IOW, the point I'm trying to make is that even if there are zero
> *actual* accesses of user space (because user space is dead, and the
> kernel hopefully does no "get_user()/put_user()" stuff at this point
> any more), the CPU may speculatively use user addresses for the
> bog-standard kernel addresses that happen.
Right.. and s390 having done this only says that s390 appears to be ok
with it. Martin, does s390 hardware guarantee no speculative stuff like
Linus explained, or might there even be a latent issue on s390?
But it looks like we cannot do this in general, and esp. ARM (as already
noted by Catalin) has very aggressive speculative behaviour.
The alternative is that we do a switch_mm() to init_mm instead of the
TLB flush. On x86 that should be about the same cost, but I've not
looked at other architectures yet.
The second and least favourite alternative is of course special casing
this for s390 if it turns out its a safe thing to do for them.
/me goes look through arch code.
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next prev parent reply other threads:[~2012-06-28 10:56 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-06-27 21:15 [PATCH 00/20] Unify TLB gather implementations -v3 Peter Zijlstra
2012-06-27 21:15 ` [PATCH 01/20] mm, x86: Add HAVE_RCU_TABLE_FREE support Peter Zijlstra
2012-06-27 21:15 ` [PATCH 02/20] mm: Add optional TLB flush to generic RCU page-table freeing Peter Zijlstra
2012-06-27 22:23 ` Linus Torvalds
2012-06-27 23:01 ` Peter Zijlstra
2012-06-27 23:42 ` Linus Torvalds
2012-06-28 7:09 ` Benjamin Herrenschmidt
2012-06-28 11:05 ` Peter Zijlstra
2012-06-28 12:00 ` Benjamin Herrenschmidt
2012-07-24 5:12 ` Nikunj A Dadhania
2012-06-27 21:15 ` [PATCH 03/20] mm, tlb: Remove a few #ifdefs Peter Zijlstra
2012-06-27 21:15 ` [PATCH 04/20] mm, s390: use generic RCU page-table freeing code Peter Zijlstra
2012-06-27 21:15 ` [PATCH 05/20] mm, powerpc: Dont use tlb_flush for external tlb flushes Peter Zijlstra
2012-06-27 21:15 ` [PATCH 06/20] mm, sparc64: " Peter Zijlstra
2012-06-27 21:15 ` [PATCH 07/20] mm, arch: Remove tlb_flush() Peter Zijlstra
2012-06-27 21:15 ` [PATCH 08/20] mm: Optimize fullmm TLB flushing Peter Zijlstra
2012-06-27 22:26 ` Linus Torvalds
2012-06-27 23:02 ` Peter Zijlstra
2012-06-27 23:13 ` Peter Zijlstra
2012-06-27 23:23 ` Linus Torvalds
2012-06-27 23:33 ` Linus Torvalds
2012-06-28 9:16 ` Catalin Marinas
2012-06-28 10:39 ` Benjamin Herrenschmidt
2012-06-28 10:59 ` Peter Zijlstra
2012-06-28 14:53 ` Catalin Marinas
2012-06-28 16:20 ` Peter Zijlstra
2012-06-28 16:38 ` Peter Zijlstra
2012-06-28 16:45 ` Linus Torvalds
2012-06-28 16:52 ` Peter Zijlstra
2012-06-28 21:57 ` Benjamin Herrenschmidt
2012-06-28 21:58 ` Benjamin Herrenschmidt
2012-06-29 8:49 ` Peter Zijlstra
2012-06-29 15:26 ` Catalin Marinas
2012-06-29 22:11 ` Benjamin Herrenschmidt
2012-06-28 10:55 ` Peter Zijlstra [this message]
2012-06-28 11:19 ` Martin Schwidefsky
2012-06-28 11:30 ` Peter Zijlstra
2012-06-28 16:00 ` Avi Kivity
2012-06-27 21:15 ` [PATCH 09/20] mm, arch: Add end argument to p??_free_tlb() Peter Zijlstra
2012-06-27 21:15 ` [PATCH 10/20] mm: Provide generic range tracking and flushing Peter Zijlstra
2012-06-27 21:15 ` [PATCH 11/20] mm, s390: Convert to use generic mmu_gather Peter Zijlstra
2012-06-27 22:13 ` Peter Zijlstra
2012-06-28 7:13 ` Martin Schwidefsky
2012-06-27 21:15 ` [PATCH 12/20] mm, arm: Convert arm to generic tlb Peter Zijlstra
2012-06-27 21:15 ` [PATCH 13/20] mm, ia64: Convert ia64 " Peter Zijlstra
2012-06-27 21:15 ` [PATCH 14/20] mm, sh: Convert sh " Peter Zijlstra
2012-06-28 18:32 ` Paul Mundt
2012-06-28 20:27 ` Peter Zijlstra
2012-06-27 21:15 ` [PATCH 15/20] mm, um: Convert um " Peter Zijlstra
2012-06-27 21:15 ` [PATCH 16/20] mm, avr32: Convert avr32 " Peter Zijlstra
2012-06-27 21:15 ` [PATCH 17/20] mm, mips: Convert mips " Peter Zijlstra
2012-06-27 21:15 ` [PATCH 18/20] mm, parisc: Convert parisc " Peter Zijlstra
2012-06-27 21:15 ` [PATCH 19/20] mm, sparc32: Convert sparc32 " Peter Zijlstra
2012-06-27 21:16 ` [PATCH 20/20] mm, xtensa: Convert xtensa " Peter Zijlstra
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