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[209.132.180.67]) by mx.google.com with ESMTP id 29si15710560pgk.306.2019.07.24.07.09.44; Wed, 24 Jul 2019 07:09:58 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728077AbfGXNxJ (ORCPT + 99 others); Wed, 24 Jul 2019 09:53:09 -0400 Received: from foss.arm.com ([217.140.110.172]:41304 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726422AbfGXNxJ (ORCPT ); Wed, 24 Jul 2019 09:53:09 -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 6F72D28; Wed, 24 Jul 2019 06:53:08 -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 996793F71A; Wed, 24 Jul 2019 06:53:05 -0700 (PDT) Subject: Re: [PATCH v9 11/21] mm: pagewalk: Add p4d_entry() and pgd_entry() To: Mark Rutland 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?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> <20190723101432.GC8085@lakrids.cambridge.arm.com> From: Steven Price Message-ID: <60ee20ef-62a3-5df1-6e24-24973b69be70@arm.com> Date: Wed, 24 Jul 2019 14:53:04 +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: <20190723101432.GC8085@lakrids.cambridge.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 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. Steve