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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham 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 3F6B0C7618B for ; Wed, 24 Jul 2019 14:09:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 223A021BF6 for ; Wed, 24 Jul 2019 14:09:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387486AbfGXOJO (ORCPT ); Wed, 24 Jul 2019 10:09:14 -0400 Received: from foss.arm.com ([217.140.110.172]:41720 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727029AbfGXOJN (ORCPT ); Wed, 24 Jul 2019 10:09:13 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 4428D28; Wed, 24 Jul 2019 07:09:13 -0700 (PDT) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id CB3973F71A; Wed, 24 Jul 2019 07:09:10 -0700 (PDT) Date: Wed, 24 Jul 2019 15:09:08 +0100 From: Mark Rutland To: Steven Price Cc: x86@kernel.org, Arnd Bergmann , Ard Biesheuvel , Peter Zijlstra , Catalin Marinas , Dave Hansen , linux-kernel@vger.kernel.org, linux-mm@kvack.org, =?utf-8?B?SsOpcsO0bWU=?= Glisse , Ingo Molnar , Borislav Petkov , Andy Lutomirski , "H. Peter Anvin" , James Morse , Thomas Gleixner , Will Deacon , Andrew Morton , linux-arm-kernel@lists.infradead.org, "Liang, Kan" Subject: Re: [PATCH v9 11/21] mm: pagewalk: Add p4d_entry() and pgd_entry() Message-ID: <20190724140908.GE2624@lakrids.cambridge.arm.com> References: <20190722154210.42799-1-steven.price@arm.com> <20190722154210.42799-12-steven.price@arm.com> <20190723101432.GC8085@lakrids.cambridge.arm.com> <60ee20ef-62a3-5df1-6e24-24973b69be70@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <60ee20ef-62a3-5df1-6e24-24973b69be70@arm.com> User-Agent: Mutt/1.11.1+11 (2f07cb52) (2018-12-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 24, 2019 at 02:53:04PM +0100, Steven Price wrote: > On 23/07/2019 11:14, Mark Rutland wrote: > > On Mon, Jul 22, 2019 at 04:42:00PM +0100, Steven Price wrote: > >> pgd_entry() and pud_entry() were removed by commit 0b1fbfe50006c410 > >> ("mm/pagewalk: remove pgd_entry() and pud_entry()") because there were > >> no users. We're about to add users so reintroduce them, along with > >> p4d_entry() as we now have 5 levels of tables. > >> > >> Note that commit a00cc7d9dd93d66a ("mm, x86: add support for > >> PUD-sized transparent hugepages") already re-added pud_entry() but with > >> different semantics to the other callbacks. Since there have never > >> been upstream users of this, revert the semantics back to match the > >> other callbacks. This means pud_entry() is called for all entries, not > >> just transparent huge pages. > >> > >> Signed-off-by: Steven Price > >> --- > >> include/linux/mm.h | 15 +++++++++------ > >> mm/pagewalk.c | 27 ++++++++++++++++----------- > >> 2 files changed, 25 insertions(+), 17 deletions(-) > >> > >> diff --git a/include/linux/mm.h b/include/linux/mm.h > >> index 0334ca97c584..b22799129128 100644 > >> --- a/include/linux/mm.h > >> +++ b/include/linux/mm.h > >> @@ -1432,15 +1432,14 @@ void unmap_vmas(struct mmu_gather *tlb, struct vm_area_struct *start_vma, > >> > >> /** > >> * mm_walk - callbacks for walk_page_range > >> - * @pud_entry: if set, called for each non-empty PUD (2nd-level) entry > >> - * this handler should only handle pud_trans_huge() puds. > >> - * the pmd_entry or pte_entry callbacks will be used for > >> - * regular PUDs. > >> - * @pmd_entry: if set, called for each non-empty PMD (3rd-level) entry > >> + * @pgd_entry: if set, called for each non-empty PGD (top-level) entry > >> + * @p4d_entry: if set, called for each non-empty P4D entry > >> + * @pud_entry: if set, called for each non-empty PUD entry > >> + * @pmd_entry: if set, called for each non-empty PMD entry > > > > How are these expected to work with folding? > > > > For example, on arm64 with 64K pages and 42-bit VA, you can have 2-level > > tables where the PGD is P4D, PUD, and PMD. IIUC we'd invoke the > > callbacks for each of those levels where we found an entry in the pgd. > > > > Either the callee handle that, or we should inhibit the callbacks when > > levels are folded, and I think that needs to be explcitly stated either > > way. > > > > IIRC on x86 the p4d folding is dynamic depending on whether the HW > > supports 5-level page tables. Maybe that implies the callee has to > > handle that. > > Yes, my assumption is that it has to be up to the callee to handle that > because folding can be dynamic. I believe this also was how these > callbacks work before they were removed. However I'll add a comment > explaining that here as it's probably non-obvious. That sounds good to me. Thanks, Mark.