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 2FF2021CA04 for ; Fri, 30 May 2025 10:03:38 +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=1748599421; cv=none; b=jDmnuUAetMBz3N4lb5SEFPw1uy+RxFDQMvGxpjwWTAwoRDCEvLqNbpqIVRevOanvwgLJEIA+6JnJoJYkWNlhkUyMxMwnYIjUPGUqVgGtERAeLoBxW2tCecn7gVuF/6lD491vPPmQYHe2HFKIHR9FMhXpCsOCM9oQzSzaZYnyRcs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748599421; c=relaxed/simple; bh=2LH4iFhDDgSYMqV8yfQVIoPaIsbL9fWVCumZgbaSGbc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=u7Uo2UWFbDP0O7gk1r5aK0fssC2G/LLpl7MKLSy1xr+5SQ4nAe7ronHtQlfobXsXk9f2mx4reKlLIFqoizYkQt6h/H8Ke5TeDxd2kixHLegd68eI/khEMM1bnTek4Kie3M/9HR0YO/5btKhy0eOfsyFiwf7BRBgzLZTg/tM0yBk= 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; 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 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 0FC4A16F2; Fri, 30 May 2025 03:03:22 -0700 (PDT) Received: from [10.57.95.14] (unknown [10.57.95.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id F40B53F694; Fri, 30 May 2025 03:03:35 -0700 (PDT) Message-ID: Date: Fri, 30 May 2025 11:03:34 +0100 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 0/3] Enable huge-vmalloc permission change Content-Language: en-GB To: Dev Jain , akpm@linux-foundation.org, david@redhat.com, catalin.marinas@arm.com, will@kernel.org Cc: lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, suzuki.poulose@arm.com, steven.price@arm.com, gshan@redhat.com, linux-arm-kernel@lists.infradead.org References: <20250530090407.19237-1-dev.jain@arm.com> From: Ryan Roberts In-Reply-To: <20250530090407.19237-1-dev.jain@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 30/05/2025 10:04, Dev Jain wrote: > This series paves the path to enable huge mappings in vmalloc space by > default on arm64. > For this we must ensure that we can handle any permission > games on vmalloc space. And the linear map :) > Currently, __change_memory_common() uses > apply_to_page_range() which does not support changing permissions for > leaf mappings. nit: A "leaf mapping" is the lowest level entry in the page tables for a given address - i.e. it maps an address to some actual memory rather than to another pgtable. It includes what the Arm ARM calls "page mappings" (PTE level) and "block mappings" (PMD/PUD/.. level). apply_to_page_range() does support page mappings, so saying it doesn't support leaf mappings is incorrect. It doesn't support block mappings. > We attempt to move away from this by using walk_page_range_novma(), > similar to what riscv does right now; however, it is the responsibility > of the caller to ensure that we do not pass a range, or split the range > covering a partial leaf mapping. > > This series is tied with Yang Shi's attempt [1] at using huge mappings > in the linear mapping in case the system supports BBML2, in which case > we will be able to split the linear mapping if needed without break-before-make. > Thus, Yang's series, IIUC, will be one such user of my series; suppose we > are changing permissions on a range of the linear map backed by PMD-hugepages, > then the sequence of operations should look like the following: > > split_range(start, (start + HPAGE_PMD_SIZE) & ~HPAGE_PMD_MASK); > split_range(end & ~HPAGE_PMD_MASK, end); I don't understand what the HPAGE_PMD_MASK twiddling is doing? That's not right. It's going to give you the offset within the 2M region. You just want: split_range(start) split_range(end) right? > __change_memory_common(start, end); > > However, this series can be used independently of Yang's; since currently > permission games are being played only on pte mappings (due to apply_to_page_range > not supporting otherwise), this series provides the mechanism for enabling > huge mappings for various kernel mappings like linear map and vmalloc. In other words, you are saying that this series is a prerequisite for Yang's series (and both are prerequisites for huge vmalloc by default). Your series adds a new capability that Yang's series will rely on (the ability to change permissions on block mappings). Thanks, Ryan > > [1] https://lore.kernel.org/all/20250304222018.615808-1-yang@os.amperecomputing.com/ > > Dev Jain (3): > mm: Allow pagewalk without locks > arm64: pageattr: Use walk_page_range_novma() to change memory > permissions > mm/pagewalk: Add pre/post_pte_table callback for lazy MMU on arm64 > > arch/arm64/mm/pageattr.c | 81 +++++++++++++++++++++++++++++++++++++--- > include/linux/pagewalk.h | 4 ++ > mm/pagewalk.c | 18 +++++++-- > 3 files changed, 94 insertions(+), 9 deletions(-) >