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 C16E0CA1016 for ; Mon, 8 Sep 2025 07:40:52 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 24FE28E0010; Mon, 8 Sep 2025 03:40:52 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 1D9208E0001; Mon, 8 Sep 2025 03:40:52 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0A1048E0010; Mon, 8 Sep 2025 03:40:52 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id EAE218E0001 for ; Mon, 8 Sep 2025 03:40:51 -0400 (EDT) Received: from smtpin26.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 90D15C0A47 for ; Mon, 8 Sep 2025 07:40:51 +0000 (UTC) X-FDA: 83865286302.26.D0CED27 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf19.hostedemail.com (Postfix) with ESMTP id D43951A0006 for ; Mon, 8 Sep 2025 07:40:49 +0000 (UTC) Authentication-Results: imf19.hostedemail.com; dkim=none; spf=pass (imf19.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=1757317250; a=rsa-sha256; cv=none; b=6TmGxms1ci3nRwx6SplZiT0IMXdw/lVORZfjwYOG/8mPzXRGwd+3i5+YCJ/wwchOMIPOUx quwhzWTCSxOcZdgfAmcpgEqSdgoioLdk3XmIElbzwG218HTen+trvQxHmigAja6R3IP+k0 yO2T5el/sxYZ66oke7O5FfrY12AGtSU= ARC-Authentication-Results: i=1; imf19.hostedemail.com; dkim=none; spf=pass (imf19.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=1757317250; 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=aYjUWXf87/0whFJO2Zp8W6St8kP9yu1+z2fRI5JVOOOAq94sQhzNqcrYkUeRyEUrkJSfus A6wCLpJTXGX7q8JBtvjynrum3/ZZbHD/hviGtUVsCT/RFLifR/49L5ePA1aoKOVkou/ACG WKIi6b6t2eZUd1phd+vkTo+YDku8big= 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 AEDB91764; Mon, 8 Sep 2025 00:40:40 -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 5A6C13F63F; Mon, 8 Sep 2025 00:40:44 -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 , Yeoreum Yun , linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, sparclinux@vger.kernel.org, xen-devel@lists.xenproject.org Subject: [PATCH v2 3/7] arm64: mm: fully support nested lazy_mmu sections Date: Mon, 8 Sep 2025 08:39:27 +0100 Message-ID: <20250908073931.4159362-4-kevin.brodsky@arm.com> X-Mailer: git-send-email 2.47.0 In-Reply-To: <20250908073931.4159362-1-kevin.brodsky@arm.com> References: <20250908073931.4159362-1-kevin.brodsky@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: D43951A0006 X-Stat-Signature: ub48oiywr9eobksu6q8kdp8a1dha3dpq X-Rspam-User: X-HE-Tag: 1757317249-481732 X-HE-Meta: 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 g2z13BNH sdUuX6LBc2LfBhRMnOAstwWlrLmGWvQD89LeEAKHZdem1ozu7IO/cKp9/ptRLu+tOEDuHNQvsx/11HpQ17qSlLwaNSJTzY3kObzDp+Drfg72G+UOBLpabwS5hrJ2m+5P+gh6LmfchlMkEKPL3cj06jALtEZuLw3bfOHfGwdjLi2bPqVd73jzHXzmePZvQMtRM9RC+4K3A3BWOR00= 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