From: Benjamin Herrenschmidt <benh@au1.ibm.com>
To: Linus Torvalds <torvalds@linux-foundation.org>,
Nick Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Andrew Lutomirski <luto@kernel.org>,
the arch/x86 maintainers <x86@kernel.org>,
Borislav Petkov <bp@alien8.de>, Will Deacon <will.deacon@arm.com>,
Rik van Riel <riel@surriel.com>, Jann Horn <jannh@google.com>,
Adin Scannell <ascannell@google.com>,
Dave Hansen <dave.hansen@intel.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>, David Miller <davem@davemloft.net>,
Martin Schwidefsky <schwidefsky@de.ibm.com>,
Michael Ellerman <mpe@ellerman.id.au>
Subject: Re: [PATCH 3/4] mm/tlb, x86/mm: Support invalidating TLB caches for RCU_TABLE_FREE
Date: Thu, 23 Aug 2018 14:54:20 +1000 [thread overview]
Message-ID: <776104d4c8e4fc680004d69e3a4c2594b638b6d1.camel@au1.ibm.com> (raw)
In-Reply-To: <CA+55aFxneZTFxxxAjLZmj92VUJg6z7hERxJ2cHoth-GC0RuELw@mail.gmail.com>
On Wed, 2018-08-22 at 20:59 -0700, Linus Torvalds wrote:
> On Wed, Aug 22, 2018 at 8:45 PM Nicholas Piggin <npiggin@gmail.com> wrote:
> >
> > powerpc/radix has no such issue, it already does this tracking.
>
> Yeah, I now realize that this was why you wanted to add that hacky
> thing to the generic code, so that you can add the tlb_flush_pgtable()
> call.
>
> I thought it was because powerpc had some special flush instruction
> for it, and the regular tlb flush didn't do it. But no. It was because
> the regular code had lost the tlb flush _entirely_, because powerpc
> didn't want it.
Heh :-) Well, back on hash we didn't (we do now with Radix) but I
wouldn't blame us for the generic code being broken ... the RCU table
freeing was in arch/powerpc at the time :-) I don't think it was us
making it generic :)
> > We were discussing this a couple of months ago, I wasn't aware of ARM's
> > issue but I suggested x86 could go the same way as powerpc.
>
> The problem is that x86 _used_ to do this all correctly long long ago.
>
> And then we switched over to the "generic" table flushing (which
> harkens back to the powerpc code).
Yes, we wrote it the RCU stuff to solve the races with SW walking,
which is completely orthogonal with HW walking & TLB content. We didn't
do the move to generic code though ;-)
> Which actually turned out to be not generic at all, and did not flush
> the internal pages like x86 used to (back when x86 just used
> tlb_remove_page for everything).
Well, having RCU do the flushing is rather generic, it makes sense
whenever there's somebody doing a SW walk *and* you don't have IPIs to
synchronize your flushes (ie, anybody with HW TLB invalidation
broadcast basically, so ARM and us).
> So as a result, x86 had unintentionally lost the TLB flush we used to
> have, because tlb_remove_table() had lost the tlb flushing because of
> a powerpc quirk.
This is a somewhat odd way of putting the "blame" :-) But yeah ok...
> You then added it back as a hacky per-architecture hook (apparently
> having realized that you never did it at all), which didn't fix the
> unintentional lack of flushing on x86.
>
> So now we're going to do it right. No more "oh, powerpc didn't need
> to flush because the hash tables weren't in the tlb at all" thing in
> the generic code that then others need to work around.
So we do need a different flush instruction for the page tables vs. the
normal TLB pages.
Cheers,
Ben.
next prev parent reply other threads:[~2018-08-23 4:54 UTC|newest]
Thread overview: 96+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-22 15:30 [PATCH 0/4] x86: TLB invalidate fixes Peter Zijlstra
2018-08-22 15:30 ` [PATCH 1/4] x86/mm/tlb: Revert the recent lazy TLB patches Peter Zijlstra
2018-08-22 21:37 ` Linus Torvalds
2018-08-22 22:11 ` Rik van Riel
2018-08-22 15:30 ` [PATCH 2/4] mm/tlb: Remove tlb_remove_table() non-concurrent condition Peter Zijlstra
2018-08-23 3:31 ` Nicholas Piggin
2018-08-23 3:35 ` Linus Torvalds
2018-08-23 3:44 ` Linus Torvalds
2018-08-23 4:16 ` Nicholas Piggin
2018-08-23 4:54 ` Linus Torvalds
2018-08-23 5:15 ` Nicholas Piggin
2018-08-24 8:42 ` Peter Zijlstra
2018-08-23 13:40 ` Will Deacon
2018-08-22 15:30 ` [PATCH 3/4] mm/tlb, x86/mm: Support invalidating TLB caches for RCU_TABLE_FREE Peter Zijlstra
2018-08-22 15:55 ` Peter Zijlstra
2018-08-23 3:45 ` Nicholas Piggin
2018-08-23 3:59 ` Linus Torvalds
2018-08-23 4:33 ` Nicholas Piggin
2018-08-23 5:03 ` Linus Torvalds
2018-08-23 5:58 ` Nicholas Piggin
2018-08-23 4:54 ` Benjamin Herrenschmidt [this message]
2018-08-23 5:11 ` Linus Torvalds
2018-08-23 5:20 ` Linus Torvalds
2018-08-23 6:48 ` Martin Schwidefsky
2018-08-23 5:21 ` Benjamin Herrenschmidt
2018-08-23 6:15 ` Nicholas Piggin
2018-08-23 13:39 ` Will Deacon
2018-08-24 8:47 ` Peter Zijlstra
2018-08-24 11:32 ` Peter Zijlstra
2018-08-24 11:39 ` Peter Zijlstra
2018-08-27 5:00 ` Nicholas Piggin
2018-08-27 7:47 ` Peter Zijlstra
2018-08-27 8:04 ` Nicholas Piggin
2018-08-27 8:09 ` Benjamin Herrenschmidt
2018-08-27 8:20 ` Peter Zijlstra
2018-08-27 8:54 ` Nicholas Piggin
2018-08-27 9:02 ` Nicholas Piggin
2018-08-27 22:13 ` Benjamin Herrenschmidt
2018-08-27 13:36 ` Rik van Riel
2018-08-27 14:29 ` Nicholas Piggin
2018-08-27 8:57 ` removig ia64, was: " Christoph Hellwig
2018-08-27 11:28 ` Peter Zijlstra
2018-08-27 11:45 ` Jason Duerstock
2018-08-27 11:00 ` Peter Zijlstra
2018-08-30 0:13 ` Vineet Gupta
2018-08-30 10:23 ` Peter Zijlstra
2018-08-24 17:26 ` Nadav Amit
2018-08-24 18:04 ` Peter Zijlstra
2018-08-24 18:35 ` TLB flushes on fixmap changes Nadav Amit
2018-08-24 19:31 ` Linus Torvalds
2018-08-24 20:24 ` Nadav Amit
2018-08-25 0:58 ` Linus Torvalds
2018-08-25 2:29 ` nadav.amit
2018-08-25 4:23 ` Andy Lutomirski
2018-08-26 2:23 ` Masami Hiramatsu
2018-08-26 4:21 ` Andy Lutomirski
2018-08-26 4:43 ` Kees Cook
2018-08-26 5:53 ` Nadav Amit
2018-08-26 14:20 ` Andy Lutomirski
2018-08-26 16:47 ` Kees Cook
2018-08-26 17:25 ` Andy Lutomirski
2018-08-26 20:15 ` Thomas Gleixner
2018-08-26 22:03 ` Kees Cook
2018-08-26 22:15 ` Matthew Wilcox
2018-08-26 22:29 ` Jann Horn
2018-08-26 9:09 ` Peter Zijlstra
2018-08-27 3:03 ` Masami Hiramatsu
2018-08-27 3:26 ` Nadav Amit
2018-08-27 8:05 ` Masami Hiramatsu
2018-08-27 17:34 ` Nadav Amit
2018-08-27 18:45 ` Andy Lutomirski
2018-08-27 18:54 ` Nadav Amit
2018-08-27 18:58 ` Andy Lutomirski
2018-08-27 19:10 ` Nadav Amit
2018-08-27 19:43 ` Nadav Amit
2018-08-27 19:58 ` Andy Lutomirski
2018-08-27 20:16 ` Nadav Amit
2018-08-27 21:55 ` Nadav Amit
2018-08-27 22:32 ` Andy Lutomirski
2018-08-27 22:54 ` Nadav Amit
2018-08-27 23:01 ` Andy Lutomirski
2018-08-28 8:49 ` Masami Hiramatsu
2018-08-28 17:33 ` Nadav Amit
2018-08-27 8:13 ` Peter Zijlstra
2018-08-27 9:39 ` Masami Hiramatsu
2018-08-27 9:55 ` Jann Horn
2018-08-26 22:48 ` Jann Horn
2018-08-24 8:35 ` [PATCH 3/4] mm/tlb, x86/mm: Support invalidating TLB caches for RCU_TABLE_FREE Peter Zijlstra
2018-08-24 13:13 ` Peter Zijlstra
2018-08-24 13:14 ` Peter Zijlstra
2018-08-24 15:49 ` Will Deacon
2018-08-23 23:31 ` Will Deacon
2018-08-22 21:34 ` Linus Torvalds
2018-08-23 8:46 ` Nicholas Piggin
2018-08-22 15:30 ` [PATCH 4/4] x86/mm: Only use tlb_remove_table() for paravirt Peter Zijlstra
2018-08-22 22:12 ` Eduardo Valentin
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