From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 93DED367B7D for ; Thu, 28 May 2026 08:05:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779955530; cv=none; b=kG7j1t3DO266hjqzSZK+3QV5j+PU9pYb/nk+vB3JAPMeYxx02R9A7tGxZFJCM5Bd3DAt/OP3svylB09WerIDhgil27cfdvyAuQdSBKnRjhfa+jcRhT5Eht39UIQ9d+dt0pLq/2KuwELf4ZipXoyjDGxK0Kk4K3WMNIbfxqoRDf8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779955530; c=relaxed/simple; bh=qc2m1Ro4tsasKKh7m1ERSxkzDtjwNkTw7WOQcFs2l+c=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=jVxFEbLGFE34fsMz5puq4kU5v/kVZ+VjYTtF0Tc36eJlnmrDYH6Jo9KAojRgHW1Y2+R1LBNdvACaB/20/6k+XG0XY5yANmiSup6uHKzmJsbwqk8EwH87hRUV1bjbnvoDF00SeWvm602UBy6oMKDERMQfiAMUTFuOmX0dSXRf5lo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=JOBb7fam; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="JOBb7fam" 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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