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 2266A27FB31 for ; Wed, 25 Jun 2025 11:04:14 +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=1750849456; cv=none; b=L3l5fc7riOLTyj+Pbe1E1XmbX1pD5IjctaDK6JWkBmpWgjeNUWC7qt0m+IM/GCPXUQjQKMPUL8omF44X4t0KEbSG2hRbv1Z09VQazODQ0bHXnUaGS0LVE653ivaVuqWimZhdIa7eo4oQ5QXx/aeMdM76In5BAyWlBTJwSmajxQI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750849456; c=relaxed/simple; bh=ag22uG28h+O57NGii3vA1MicGGZ/ef7YItgruBjSBwY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=q6/LNYlMIZ1xl8vH5H6v95wlAvXNkl1mtLsMbX32ga6qDnzKlfhypU9/GAPN7Thw7T9pRq8K4w179Qxg14lSpTYkSB88h8NFCs38H1Jr+K8zHPcIpaRQgxNR5PRmGJ3jckOsvYokHlXNGPoKEwFIk4l4XgdmPQoMfktIeBp3pGA= 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 E40AB106F; Wed, 25 Jun 2025 04:03:55 -0700 (PDT) Received: from [10.57.84.221] (unknown [10.57.84.221]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id DED9C3F58B; Wed, 25 Jun 2025 04:04:10 -0700 (PDT) Message-ID: <956f6ebe-606f-4575-a0a5-7841c95b5371@arm.com> Date: Wed, 25 Jun 2025 12:04:09 +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 v3 1/2] arm64: pageattr: Use pagewalk API to change memory permissions Content-Language: en-GB To: Mike Rapoport , Dev Jain Cc: akpm@linux-foundation.org, david@redhat.com, catalin.marinas@arm.com, will@kernel.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, 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, yang@os.amperecomputing.com, anshuman.khandual@arm.com References: <20250613134352.65994-1-dev.jain@arm.com> <20250613134352.65994-2-dev.jain@arm.com> From: Ryan Roberts In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 15/06/2025 08:32, Mike Rapoport wrote: > On Fri, Jun 13, 2025 at 07:13:51PM +0530, Dev Jain wrote: >> -/* >> - * This function assumes that the range is mapped with PAGE_SIZE pages. >> - */ >> -static int __change_memory_common(unsigned long start, unsigned long size, >> +static int ___change_memory_common(unsigned long start, unsigned long size, >> pgprot_t set_mask, pgprot_t clear_mask) >> { >> struct page_change_data data; >> @@ -61,9 +140,28 @@ static int __change_memory_common(unsigned long start, unsigned long size, >> data.set_mask = set_mask; >> data.clear_mask = clear_mask; >> >> - ret = apply_to_page_range(&init_mm, start, size, change_page_range, >> - &data); >> + arch_enter_lazy_mmu_mode(); >> + >> + /* >> + * The caller must ensure that the range we are operating on does not >> + * partially overlap a block mapping. Any such case should either not >> + * exist, or must be eliminated by splitting the mapping - which for >> + * kernel mappings can be done only on BBML2 systems. >> + * >> + */ >> + ret = walk_kernel_page_table_range_lockless(start, start + size, >> + &pageattr_ops, NULL, &data); > > x86 has a cpa_lock for set_memory/set_direct_map to ensure that there's on > concurrency in kernel page table updates. I think arm64 has to have such > lock as well. We don't have a lock today, using apply_to_page_range(); we are expecting that the caller has exclusive ownership of the portion of virtual memory - i.e. the vmalloc region or linear map. So I don't think this patch changes that requirement? Where it does get a bit more hairy is when we introduce the support for splitting. In that case, 2 non-overlapping areas of virtual memory may share a large leaf mapping that needs to be split. But I've been discussing that with Yang Shi at [1] and I think we can handle that locklessly too. Perhaps I'm misunderstanding something? [1] https://lore.kernel.org/all/f036acea-1bd1-48a7-8600-75ddd504b8db@arm.com/ Thanks, Ryan > >> + arch_leave_lazy_mmu_mode(); >> + >> + return ret; >> +} >