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 7B4893C943B for ; Wed, 27 May 2026 07:35:56 +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=1779867358; cv=none; b=BZ9bEUvXVUe3VWU7s2EpKXKbs2bWXTxKyqBkHt1djGXGtIUJ0ZVV7t3mlo+psHhDPFAXkdseFRkdj2ygU/eL+j+fbTcxApOoMVmICdakCqpXqH6qfDY+XsDTaRcuh/MQ+pSsg5Xr9NQznNgqvkza83N+9NNnTzgP4EE1baAG9Ks= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779867358; c=relaxed/simple; bh=PdNASjHzMFcTuvj2O7glLeKGsNZHbnvtXnjzn6isxgQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=rWte/rS3p98gstGlkeB0Cdc1lRz/FdCeWU7XM+v4chfeGdsxKFgsMG4+OBgggSYWa94ieazktFYaBTfRAZHYVNHI+MEhY/Ua/X5JzqITIeC5GxmZSpZzoQACf13JkwI1e6xymgRAOgVV68HjaqRew3ikadH9jFJHyInaOb/nTXY= 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=e8mQOnEn; 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="e8mQOnEn" 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 8FF8027DC; Wed, 27 May 2026 00:35:50 -0700 (PDT) Received: from [10.57.93.47] (unknown [10.57.93.47]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 616C73F632; Wed, 27 May 2026 00:35:53 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1779867355; bh=PdNASjHzMFcTuvj2O7glLeKGsNZHbnvtXnjzn6isxgQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=e8mQOnEn2+oYphGx+uDlYnYs9VLRpw312YQn0n6jfNrmHENZB5GLwydumToXyGc+M fs4ywuXgUPm+W9ui68dzf6q+eitrm/9SlD45ExCS+KUh0ulqDpc62NGqrAeQUKDemZ aA9u3+ZbfAXqJdsCwQUVOPcq/KLO2WVJl5clNdDQ= Message-ID: <423a2656-e1a3-473e-abeb-5e301c6f7c2a@arm.com> Date: Wed, 27 May 2026 09:35:50 +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: Will Deacon Cc: Vishal Moola , 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> From: Kevin Brodsky Content-Language: en-GB In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit 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(). In the meantime we should probably use the logic above to avoid the BUG that Alistair reported. - Kevin