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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 94F5CCD5BD5 for ; Thu, 28 May 2026 08:05:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=CvUp2WE4NRfIp2nl9XGNBy0iKarZdKYxJdNZYx9xR2I=; b=XL82l3M0aombo1iDPNe9kRisQd xl1ma97kK3ConEUz9TtIWT3GxHmN6gSvTqRe9nbrfQa8dTZfSuen4aluYgmnj8Bo8YIOSSkqZ7Drk /qp6TcUZ2gVg8XasJIQGWHp7uu8W7nopiyh90odR96dzy7wg0t/U7UxDboaw67m/D8wcbg+Pk4m8Y xDHwpZD142bJKAzFYXmxxRR0U1sGSb+3Pmh8hbuF+O3mPezyIO2r+XcYlKRe4Z60BMSDHC/Bk2aom wLXP/AfiGUSh8tTOGYqKO36fihepeSKxifk+aKcKdWLB1q7qhfiYVHmfQ5q4e01Tcnmns0MJ8SPWt qEm91AKw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wSVkF-00000005LCV-2si3; Thu, 28 May 2026 08:05:35 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wSVkC-00000005LBi-1ogZ for linux-arm-kernel@lists.infradead.org; Thu, 28 May 2026 08:05:33 +0000 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 C752522EE; Thu, 28 May 2026 01:05:22 -0700 (PDT) Received: from [10.57.93.112] (unknown [10.57.93.112]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 7B4D53F905; Thu, 28 May 2026 01:05:25 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1779955527; bh=qc2m1Ro4tsasKKh7m1ERSxkzDtjwNkTw7WOQcFs2l+c=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=JOBb7famIPNptjHwcOfdiS9+PoHZz/46QZ+nvB6L2cHKpDuU+BPPF+CJCpsgICZ/Q 47qo21i6t5dGT5rBtZqk+BMAi2prTImKC4R8XqCQ/zP5HHjZnZRrQR/uBPHSfibHi9 d9p1JXouhYK52CpfqUgq2kq9j4Qhl7TleZoeSApM= Message-ID: <83d168c1-fed9-4301-8d0e-ffd133df90bb@arm.com> Date: Thu, 28 May 2026 10:05:22 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] arm64: mm: call pagetable dtor when freeing hot-removed page tables To: Vishal Moola , Matthew Wilcox Cc: Will Deacon , Catalin Marinas , Andrew Morton , Alistair Popple , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, david@kernel.org References: <20260521032730.2104017-1-apopple@nvidia.com> <20260521153130.d7d5cd060f7522f894252333@linux-foundation.org> <92450154-e1ab-46e4-b23d-eaa59c9cdd3b@arm.com> <423a2656-e1a3-473e-abeb-5e301c6f7c2a@arm.com> From: Kevin Brodsky Content-Language: en-GB In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260528_010532_573692_64820C8D X-CRM114-Status: GOOD ( 21.92 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 27/05/2026 11:30, Vishal Moola wrote: > On Wed, May 27, 2026 at 09:35:50AM +0200, Kevin Brodsky wrote: >> On 26/05/2026 17:07, Will Deacon wrote: >>> On Tue, May 26, 2026 at 01:54:00PM +0200, Kevin Brodsky wrote: >>>> On 22/05/2026 11:36, Vishal Moola wrote: >>>>>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c >>>>>> index 4c8959153ac4..9d42cbddce27 100644 >>>>>> --- a/arch/arm64/mm/mmu.c >>>>>> +++ b/arch/arm64/mm/mmu.c >>>>>> @@ -1441,6 +1441,9 @@ static void free_hotplug_page_range(struct page *page, size_t size, >>>>>> >>>>>> static void free_hotplug_pgtable_page(struct page *page) >>>>>> { >>>>>> + if (folio_test_pgtable(page_folio(page))) >>>>> This should work. >>>>> >>>>>> + pagetable_dtor(page_ptdesc(page)); >>>>>> + >>>>>> free_hotplug_page_range(page, PAGE_SIZE, NULL); >>>>> In the case we presumably have a page table page (ptdesc) at this >>>>> point, we should really be freeing it with pagetable_free() as well. >>>> Agreed, I think this is the right thing to do, something like: >>>> >>>> if (folio_test_pgtable(page_folio(page))) >>>> pagetable_dtor_free(page_ptdesc(page)); else >>>> free_hotplug_page_range(page, PAGE_SIZE, NULL); >>>> >>>> >>>> Strangely enough x86 calls pagetable_free() in both cases. >>>> >>>> My series protecting page tables with pkeys has a patch [1] to get >>>> vmemmap to allocate page tables with pagetable_alloc(). The diff above >>>> will require pagetable_*_ctor() to be called as well, but I think that's >>>> the right thing to do anyway. That could be posted as a separate series, >>>> but I'm hesitant due to the lack of NUMA awareness in pagetable_alloc(). >>> I agree that calling the ctor()/dtor() functions consistently is the >>> cleanest approach and that will need something like your patch to call >>> the constructor from vmemmap_alloc_block_zero(). Trying to elide these >>> calls for the page-table pages used to map the altmap just feels odd to >>> me, as there isn't anything particularly special about them afaik. >> I don't think they're really special either, most likely they just got >> missed/ignored for the purpose of ctor/dtor like many other kernel page >> tables (until recently). >> >> I'll prepare a series refactoring that code then - that will also >> require changing most arch implementations of vmemmap_free() to call >> pagetable_dtor_free(). > Take a look at Matthew's series[1]. I think thats the ideal approach for > page table accounting. He hasn't had time to iterate on it though. I > doubt he'd mind if someone picked it up. I recall this series. Are you suggesting that we would no longer need to call the ctor/dtor for kernel page tables with this approach? That leaves us with the weird case of ptdesc_set_kernel(), which is called from *_alloc_one() while ptdesc_clear_kernel() is called from pagetable_free(), but that's only an optimisation so we can probably live with it. If we go down this route, I would suggest we inline what's left of the ctor/dtor, i.e. ptlock, in {pte,pmd}_alloc_one() and {pte,pmd}_free(). This way it is clear that everything applicable to all page tables (kernel+user) should go directly into pagetable_{alloc,free}. Happy to post something along those lines (patch 2/3 of Matthew's series + removing ctor/dtor completely) if that sounds sensible. - Kevin