From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 20D67C3A59E for ; Tue, 20 Aug 2019 09:12:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E9BD2214DA for ; Tue, 20 Aug 2019 09:12:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729526AbfHTJMh (ORCPT ); Tue, 20 Aug 2019 05:12:37 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:51213 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728771AbfHTJMg (ORCPT ); Tue, 20 Aug 2019 05:12:36 -0400 Received: from p5de0b6c5.dip0.t-ipconnect.de ([93.224.182.197] helo=nanos.glx-home) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1i00Bp-00089o-HM; Tue, 20 Aug 2019 11:12:29 +0200 Date: Tue, 20 Aug 2019 11:12:13 +0200 (CEST) From: Thomas Gleixner To: Song Liu cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel-team@fb.com, stable@vger.kernel.org, Joerg Roedel , Dave Hansen , Andy Lutomirski , Peter Zijlstra Subject: Re: [PATCH] x86/mm/pti: in pti_clone_pgtable() don't increase addr by PUD_SIZE In-Reply-To: <20190820075128.2912224-1-songliubraving@fb.com> Message-ID: References: <20190820075128.2912224-1-songliubraving@fb.com> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 20 Aug 2019, Song Liu wrote: > pti_clone_pgtable() increases addr by PUD_SIZE for pud_none(*pud) case. > This is not accurate because addr may not be PUD_SIZE aligned. You fail to explain how this happened. The code before the 32bit support did always increase by PMD_SIZE. The 32bit support broke that. > In our x86_64 kernel, pti_clone_pgtable() fails to clone 7 PMDs because > of this issuse, including PMD for the irq entry table. For a memcache > like workload, this introduces about 4.5x more iTLB-load and about 2.5x > more iTLB-load-misses on a Skylake CPU. This information is largely irrelevant. What matters is the fact that this got broken and incorrectly forwards the address by PUD_SIZE which is wrong if address is not PUD_SIZE aligned. > This patch fixes this issue by adding PMD_SIZE to addr for pud_none() > case. git grep 'This patch' Documentation/process/submitting-patches.rst > Cc: stable@vger.kernel.org # v4.19+ > Fixes: 16a3fe634f6a ("x86/mm/pti: Clone kernel-image on PTE level for 32 bit") > Signed-off-by: Song Liu > Cc: Joerg Roedel > Cc: Thomas Gleixner > Cc: Dave Hansen > Cc: Andy Lutomirski > Cc: Peter Zijlstra > --- > arch/x86/mm/pti.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c > index b196524759ec..5a67c3015f59 100644 > --- a/arch/x86/mm/pti.c > +++ b/arch/x86/mm/pti.c > @@ -330,7 +330,7 @@ pti_clone_pgtable(unsigned long start, unsigned long end, > > pud = pud_offset(p4d, addr); > if (pud_none(*pud)) { > - addr += PUD_SIZE; > + addr += PMD_SIZE; The right fix is to skip forward to the next PUD boundary instead of doing this in a loop with PMD_SIZE increments. Thanks, tglx