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 89920C433FF for ; Mon, 29 Jul 2019 12:17:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6CBDC2070D for ; Mon, 29 Jul 2019 12:17:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727715AbfG2MRt (ORCPT ); Mon, 29 Jul 2019 08:17:49 -0400 Received: from foss.arm.com ([217.140.110.172]:43132 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726635AbfG2MRs (ORCPT ); Mon, 29 Jul 2019 08:17:48 -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 F232528; Mon, 29 Jul 2019 05:17:45 -0700 (PDT) Received: from [10.1.196.133] (e112269-lin.cambridge.arm.com [10.1.196.133]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 4EFF93F575; Mon, 29 Jul 2019 05:17:43 -0700 (PDT) Subject: Re: [PATCH v9 11/21] mm: pagewalk: Add p4d_entry() and pgd_entry() To: Anshuman Khandual , linux-mm@kvack.org, =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= Cc: Mark Rutland , x86@kernel.org, Arnd Bergmann , Ard Biesheuvel , Peter Zijlstra , Catalin Marinas , Dave Hansen , linux-kernel@vger.kernel.org, =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , 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" References: <20190722154210.42799-1-steven.price@arm.com> <20190722154210.42799-12-steven.price@arm.com> From: Steven Price Message-ID: <63a86424-9a8e-4528-5880-138f0009e462@arm.com> Date: Mon, 29 Jul 2019 13:17:42 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 28/07/2019 13:33, Anshuman Khandual wrote: > > > On 07/22/2019 09:12 PM, 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 >> * this handler is required to be able to handle >> * pmd_trans_huge() pmds. They may simply choose to >> * split_huge_page() instead of handling it explicitly. >> - * @pte_entry: if set, called for each non-empty PTE (4th-level) entry >> + * @pte_entry: if set, called for each non-empty PTE (lowest-level) entry >> * @pte_hole: if set, called for each hole at all levels >> * @hugetlb_entry: if set, called for each hugetlb entry >> * @test_walk: caller specific callback function to determine whether >> @@ -1455,6 +1454,10 @@ void unmap_vmas(struct mmu_gather *tlb, struct vm_area_struct *start_vma, >> * (see the comment on walk_page_range() for more details) >> */ >> struct mm_walk { >> + int (*pgd_entry)(pgd_t *pgd, unsigned long addr, >> + unsigned long next, struct mm_walk *walk); >> + int (*p4d_entry)(p4d_t *p4d, unsigned long addr, >> + unsigned long next, struct mm_walk *walk); >> int (*pud_entry)(pud_t *pud, unsigned long addr, >> unsigned long next, struct mm_walk *walk); >> int (*pmd_entry)(pmd_t *pmd, unsigned long addr, >> diff --git a/mm/pagewalk.c b/mm/pagewalk.c >> index c3084ff2569d..98373a9f88b8 100644 >> --- a/mm/pagewalk.c >> +++ b/mm/pagewalk.c >> @@ -90,15 +90,9 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end, >> } >> >> if (walk->pud_entry) { >> - spinlock_t *ptl = pud_trans_huge_lock(pud, walk->vma); >> - >> - if (ptl) { >> - err = walk->pud_entry(pud, addr, next, walk); >> - spin_unlock(ptl); >> - if (err) >> - break; >> - continue; >> - } >> + err = walk->pud_entry(pud, addr, next, walk); >> + if (err) >> + break; > > But will not this still encounter possible THP entries when walking user > page tables (valid walk->vma) in which case still needs to get a lock. > OR will the callback take care of it ? This is what I mean in the commit message by: > 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. So the expectation is that the caller takes care of it. However, having checked again, it appears that mm/hmm.c now does use this callback (merged in v5.2-rc1). Jérôme - are you happy with this change in semantics? It looks like hmm_vma_walk_pud() should deal gracefully with both normal and large pages - although I'm unsure whether you are relying on the lock from pud_trans_huge_lock()? Thanks, Steve