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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id B538DCA1015 for ; Thu, 4 Sep 2025 12:58:39 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 04FF18E0015; Thu, 4 Sep 2025 08:58:39 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 027268E0013; Thu, 4 Sep 2025 08:58:38 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E31A48E0015; Thu, 4 Sep 2025 08:58:38 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id CFD658E0013 for ; Thu, 4 Sep 2025 08:58:38 -0400 (EDT) Received: from smtpin25.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 6978B8483D for ; Thu, 4 Sep 2025 12:58:38 +0000 (UTC) X-FDA: 83851571916.25.BC3C2C9 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf03.hostedemail.com (Postfix) with ESMTP id 967CE20013 for ; Thu, 4 Sep 2025 12:58:36 +0000 (UTC) Authentication-Results: imf03.hostedemail.com; dkim=none; spf=pass (imf03.hostedemail.com: domain of kevin.brodsky@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=kevin.brodsky@arm.com; dmarc=pass (policy=none) header.from=arm.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1756990716; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=CcBj7SkfGcRisUp144Doi/BeLUzFNWGgepHeyPHMYvQ=; b=bBPnMbeFDS6hSBC4I5y0Z8eDnkCGULmoBdOakSJZeNNg76GpXw4b02wvFRBnKuSZZOZ+Sa UvMqCZ/ydn5nJJ79OZ7bYHh0NmQF4bQmyFu7m00UnYUJmI2GDB+lE2CX7+ILtSpHceotvM Qt0xnc2ibmNYFIf0KLmHXFX/S9KdRZY= ARC-Authentication-Results: i=1; imf03.hostedemail.com; dkim=none; spf=pass (imf03.hostedemail.com: domain of kevin.brodsky@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=kevin.brodsky@arm.com; dmarc=pass (policy=none) header.from=arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1756990716; a=rsa-sha256; cv=none; b=fveo9nMZj12fplvc1GONd5GdlVRJdKAap06ZTTtwJ2xp+xvwuK6aNoXt4YrliyZIDY56WC Fc25adOUFxnk6edgrM7vp3kF72axZtinJ3tyiuRUsx88N2asw2Aw7TL9Lpa51qkuLulegQ VYFFQVWSxrac6wFFQNqFroabtYAAVpA= 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 4A9CE2EC6; Thu, 4 Sep 2025 05:58:27 -0700 (PDT) Received: from e123572-lin.arm.com (e123572-lin.cambridge.arm.com [10.1.194.54]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 17AC83F6A8; Thu, 4 Sep 2025 05:58:30 -0700 (PDT) From: Kevin Brodsky To: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Kevin Brodsky , Alexander Gordeev , Andreas Larsson , Andrew Morton , Boris Ostrovsky , Borislav Petkov , Catalin Marinas , Christophe Leroy , Dave Hansen , David Hildenbrand , "David S. Miller" , "H. Peter Anvin" , Ingo Molnar , Jann Horn , Juergen Gross , "Liam R. Howlett" , Lorenzo Stoakes , Madhavan Srinivasan , Michael Ellerman , Michal Hocko , Mike Rapoport , Nicholas Piggin , Peter Zijlstra , Ryan Roberts , Suren Baghdasaryan , Thomas Gleixner , Vlastimil Babka , Will Deacon , linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, sparclinux@vger.kernel.org, xen-devel@lists.xenproject.org Subject: [PATCH 3/7] arm64: mm: fully support nested lazy_mmu sections Date: Thu, 4 Sep 2025 13:57:32 +0100 Message-ID: <20250904125736.3918646-4-kevin.brodsky@arm.com> X-Mailer: git-send-email 2.47.0 In-Reply-To: <20250904125736.3918646-1-kevin.brodsky@arm.com> References: <20250904125736.3918646-1-kevin.brodsky@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 967CE20013 X-Rspam-User: X-Stat-Signature: fz8griwrzu11czynettg8gzrfkhc9k4q X-Rspamd-Server: rspam09 X-HE-Tag: 1756990716-739086 X-HE-Meta: U2FsdGVkX18L7sHlcVIFns20mWRVEjcAG8KGsiFu+C6pTA/Ol08xTKZorAMKpre995PzNz6xpkBUgQSgUHS3Kmtk00HnMBSZSULGoaA+qOoLrBTkFFFzj3V9pY+LFLJ/mBjZeI86A4rT8Gd5KhbQpn6vC28RHXTZUv3nbM+7Kb7wcQDGq3sDq7NmnZHjx4LCnpfhXXVjnHkqTZHZP4N5Lr6irwIManMudaTvWx94pVgIYcBvA+MP6WLWBbKlbR4NWOz8MJ+n/4goM4aGEG6yoYyXh4CODTNboH30mGPirVBnJTICSaWlhftCV6cWizWonvO8GXSqojH9nhTUqUSipqfbiOW97+qQXjcQgS3P0O4WHZ2t3C9vDD5jJea9VskU53tadJnET2MFlPcduSHgANU4nXqGXf3B24zIDa6e68tkvkxtKUARCutC2eIJLYWXmuyG/rNoYxzv5CFKGzfyUtIQANVYgITkId8NzF6f/l+M2/r8D8HgiBqkf38KTgTYV1CUdkKSTKRpTFGoK1SAvkEEGH2mLy2qultnFQDE68AFym8d/v0ysanXp5FKjhEkWeaXcUuoz8/F9v1muZ34qOsA6aR7nHgOWmr8XNxO35Jw/1mN+QxvVHfNYsR7KuH1+olH2q7pYV6c5nTP9jlObMC2Gv0w+7tnEXAtjDBg//hVW9QeRYN0zA8nvwI5LoGGdEYCMjS/p7s3IksgTjzvm4+L9Ij1LBI4xQHSrbZSwzh/JrwAfNV1NhV7TD65N252UYhQtaK7uFCE8ghaKnub3a0D/n6fcvO1r8OnDTjt9GjYUHu0Iyj9Yq+dWXxwu29EnU5RtE/gzNB2hN00I2Zo8L4+pBPSsD9+iy5AstmqENBZeDj/nNFi2srTqRHqLHDY+ahAnWdt/dTOmtrLpCZWg9ZPa2RsrUgkwKMlzmSpnKyV9KmKV+W9bCbAfcoNw64umC8AAGT0XQVnmx+qcDV RIqLxRPw snD12EtuY4FGVJTsj7uhzMDcDsvsm5OAzZNe3RYUzeoXzrVlBWZlVBGtuol+eX0GdCi4m+laBbL42cyli9x6SGs7o3map5GXqqwMZEFbPO9GwGsFendNmOBXBYGcZA2oD/gl5isgLoIuAH63ghoG4gl7QY2U//W+UczaR4jr3PFSuWi/K10RlPKLu9IFc7SgwJWRy34QgEekKSSk= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Despite recent efforts to prevent lazy_mmu sections from nesting, it remains difficult to ensure that it never occurs - and in fact it does occur on arm64 in certain situations (CONFIG_DEBUG_PAGEALLOC). Commit 1ef3095b1405 ("arm64/mm: Permit lazy_mmu_mode to be nested") made nesting tolerable on arm64, but without truly supporting it: the inner leave() call clears TIF_LAZY_MMU, disabling the batching optimisation before the outer section ends. Now that the lazy_mmu API allows enter() to pass through a state to the matching leave() call, we can actually support nesting. If enter() is called inside an active lazy_mmu section, TIF_LAZY_MMU will already be set, and we can then return LAZY_MMU_NESTED to instruct the matching leave() call not to clear TIF_LAZY_MMU. The only effect of this patch is to ensure that TIF_LAZY_MMU (and therefore the batching optimisation) remains set until the outermost lazy_mmu section ends. leave() still emits barriers if needed, regardless of the nesting level, as the caller may expect any page table changes to become visible when leave() returns. Signed-off-by: Kevin Brodsky --- arch/arm64/include/asm/pgtable.h | 19 +++++-------------- 1 file changed, 5 insertions(+), 14 deletions(-) diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h index 816197d08165..602feda97dc4 100644 --- a/arch/arm64/include/asm/pgtable.h +++ b/arch/arm64/include/asm/pgtable.h @@ -85,24 +85,14 @@ typedef int lazy_mmu_state_t; static inline lazy_mmu_state_t arch_enter_lazy_mmu_mode(void) { - /* - * lazy_mmu_mode is not supposed to permit nesting. But in practice this - * does happen with CONFIG_DEBUG_PAGEALLOC, where a page allocation - * inside a lazy_mmu_mode section (such as zap_pte_range()) will change - * permissions on the linear map with apply_to_page_range(), which - * re-enters lazy_mmu_mode. So we tolerate nesting in our - * implementation. The first call to arch_leave_lazy_mmu_mode() will - * flush and clear the flag such that the remainder of the work in the - * outer nest behaves as if outside of lazy mmu mode. This is safe and - * keeps tracking simple. - */ + int lazy_mmu_nested; if (in_interrupt()) return LAZY_MMU_DEFAULT; - set_thread_flag(TIF_LAZY_MMU); + lazy_mmu_nested = test_and_set_thread_flag(TIF_LAZY_MMU); - return LAZY_MMU_DEFAULT; + return lazy_mmu_nested ? LAZY_MMU_NESTED : LAZY_MMU_DEFAULT; } static inline void arch_leave_lazy_mmu_mode(lazy_mmu_state_t state) @@ -113,7 +103,8 @@ static inline void arch_leave_lazy_mmu_mode(lazy_mmu_state_t state) if (test_and_clear_thread_flag(TIF_LAZY_MMU_PENDING)) emit_pte_barriers(); - clear_thread_flag(TIF_LAZY_MMU); + if (state != LAZY_MMU_NESTED) + clear_thread_flag(TIF_LAZY_MMU); } #ifdef CONFIG_TRANSPARENT_HUGEPAGE -- 2.47.0