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=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 36351C433FF for ; Mon, 29 Jul 2019 12:30:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0D6382054F for ; Mon, 29 Jul 2019 12:30:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387852AbfG2MaI (ORCPT ); Mon, 29 Jul 2019 08:30:08 -0400 Received: from foss.arm.com ([217.140.110.172]:43326 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726281AbfG2MaI (ORCPT ); Mon, 29 Jul 2019 08:30:08 -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 1D1DA28; Mon, 29 Jul 2019 05:30:07 -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 75AB43F575; Mon, 29 Jul 2019 05:29:59 -0700 (PDT) Subject: Re: [PATCH v9 12/21] mm: pagewalk: Allow walking without vma To: Anshuman Khandual , linux-mm@kvack.org 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> <20190722154210.42799-13-steven.price@arm.com> <7fc50563-7d5d-7270-5a6a-63769e9c335a@arm.com> From: Steven Price Message-ID: <5aff70f7-67a5-c7e8-5fec-8182dea0da0c@arm.com> Date: Mon, 29 Jul 2019 13:29:58 +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: <7fc50563-7d5d-7270-5a6a-63769e9c335a@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 28/07/2019 15:20, Anshuman Khandual wrote: > > > On 07/22/2019 09:12 PM, Steven Price wrote: >> Since 48684a65b4e3: "mm: pagewalk: fix misbehavior of walk_page_range >> for vma(VM_PFNMAP)", page_table_walk() will report any kernel area as >> a hole, because it lacks a vma. >> >> This means each arch has re-implemented page table walking when needed, >> for example in the per-arch ptdump walker. >> >> Remove the requirement to have a vma except when trying to split huge >> pages. >> >> Signed-off-by: Steven Price >> --- >> mm/pagewalk.c | 25 +++++++++++++++++-------- >> 1 file changed, 17 insertions(+), 8 deletions(-) >> >> diff --git a/mm/pagewalk.c b/mm/pagewalk.c >> index 98373a9f88b8..1cbef99e9258 100644 >> --- a/mm/pagewalk.c >> +++ b/mm/pagewalk.c >> @@ -36,7 +36,7 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end, >> do { >> again: >> next = pmd_addr_end(addr, end); >> - if (pmd_none(*pmd) || !walk->vma) { >> + if (pmd_none(*pmd)) { >> if (walk->pte_hole) >> err = walk->pte_hole(addr, next, walk); >> if (err) >> @@ -59,9 +59,14 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end, >> if (!walk->pte_entry) >> continue; >> >> - split_huge_pmd(walk->vma, pmd, addr); >> - if (pmd_trans_unstable(pmd)) >> - goto again; >> + if (walk->vma) { >> + split_huge_pmd(walk->vma, pmd, addr); > > Check for a PMD THP entry before attempting to split it ? split_huge_pmd does the check for us: > #define split_huge_pmd(__vma, __pmd, __address) \ > do { \ > pmd_t *____pmd = (__pmd); \ > if (is_swap_pmd(*____pmd) || pmd_trans_huge(*____pmd) \ > || pmd_devmap(*____pmd)) \ > __split_huge_pmd(__vma, __pmd, __address, \ > false, NULL); \ > } while (0) And this isn't a change from the previous code - only that the entry is no longer split when walk->vma==NULL. >> + if (pmd_trans_unstable(pmd)) >> + goto again; >> + } else if (pmd_leaf(*pmd)) { >> + continue; >> + } >> + >> err = walk_pte_range(pmd, addr, next, walk); >> if (err) >> break; >> @@ -81,7 +86,7 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end, >> do { >> again: >> next = pud_addr_end(addr, end); >> - if (pud_none(*pud) || !walk->vma) { >> + if (pud_none(*pud)) { >> if (walk->pte_hole) >> err = walk->pte_hole(addr, next, walk); >> if (err) >> @@ -95,9 +100,13 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end, >> break; >> } >> >> - split_huge_pud(walk->vma, pud, addr); >> - if (pud_none(*pud)) >> - goto again; >> + if (walk->vma) { >> + split_huge_pud(walk->vma, pud, addr); > > Check for a PUD THP entry before attempting to split it ? Same as above. >> + if (pud_none(*pud)) >> + goto again; >> + } else if (pud_leaf(*pud)) { >> + continue; >> + } > > This is bit cryptic. walk->vma check should be inside a helper is_user_page_table() > or similar to make things clear. p4d_leaf() check missing in walk_p4d_range() for > kernel page table walk ? Wondering if p?d_leaf() test should be moved earlier while > calling p?d_entry() for kernel page table walk. I wasn't sure if it was worth putting p4d_leaf() and pgd_leaf() checks in (yet). No architecture that I know of uses such large pages. I'm not sure what you mean by moving the p?d_leaf() test earlier? Can you explain with an example? Thanks, Steve