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 BA4B1CCD194 for ; Thu, 16 Oct 2025 07:32:32 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 263488E0009; Thu, 16 Oct 2025 03:32:32 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 214268E0002; Thu, 16 Oct 2025 03:32:32 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1031A8E0009; Thu, 16 Oct 2025 03:32:32 -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 EFE0B8E0002 for ; Thu, 16 Oct 2025 03:32:31 -0400 (EDT) Received: from smtpin24.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 9512E855AD for ; Thu, 16 Oct 2025 07:32:31 +0000 (UTC) X-FDA: 84003159702.24.B7F65F8 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf07.hostedemail.com (Postfix) with ESMTP id CF80E40008 for ; Thu, 16 Oct 2025 07:32:29 +0000 (UTC) Authentication-Results: imf07.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf07.hostedemail.com: domain of kevin.brodsky@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=kevin.brodsky@arm.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1760599950; 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-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=SK6RxrxNXxRFLxyAYlYq9aaMejSm4vU8SsNeGUxqVQo=; b=xSO4fj+eNGM0KGLfs1ss+OtLPC0xqZhORwdWEpWwU2zmXLph5vBajvTS5AR5u7+7dgb47c pRy1f84fPuYoTuI9Dz0h9Gj5OsUaCxEregJMfXAXeAGq7Zjcepmr9zn9ruHuH8NDlpn4k9 KR5UQ1YyzH42e9fjfH5OocDRyk5EIOM= ARC-Authentication-Results: i=1; imf07.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf07.hostedemail.com: domain of kevin.brodsky@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=kevin.brodsky@arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1760599950; a=rsa-sha256; cv=none; b=ry0XCrhnp8rwByBzr/UhdvDRkSdQU7J8z8Zgqj4hiedM+wWJAFuqNxvhLm1BCR8T3tYPXp xLodfpVpTDlv5rrdo6dLtrelSCKq303//h19AU6u1CoiRLIFWUwazNTTxWciwp9QQQigDN X9F/LzWyxlE+E0XTgw+isbIMA1vykPQ= 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 B64F21688; Thu, 16 Oct 2025 00:32:20 -0700 (PDT) Received: from [10.57.65.134] (unknown [10.57.65.134]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 3F1683F6A8; Thu, 16 Oct 2025 00:32:20 -0700 (PDT) Message-ID: <54f183bb-33ce-4b9c-91a9-827a6ed198d6@arm.com> Date: Thu, 16 Oct 2025 09:32:13 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 02/13] x86/xen: simplify flush_lazy_mmu() To: Dave Hansen , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, 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, x86@kernel.org References: <20251015082727.2395128-1-kevin.brodsky@arm.com> <20251015082727.2395128-3-kevin.brodsky@arm.com> <35d9cf4f-135e-4786-a4e3-fd3a4a18b800@intel.com> Content-Language: en-GB From: Kevin Brodsky In-Reply-To: <35d9cf4f-135e-4786-a4e3-fd3a4a18b800@intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: CF80E40008 X-Stat-Signature: bwgu8de7f1t16wwya6hmom5pih954sf1 X-Rspam-User: X-HE-Tag: 1760599949-705585 X-HE-Meta: U2FsdGVkX18uTwtmk0sj07Dq+zGJtlYXd2GBr4h9SQiFwKQBzdHgDOr9IwwB1ZUfy59UGiUCJUMG877en6gbwvE443aB5SKuVbIoJEzgqkqKhQL/GfyUtb0ukaivpO86hAnqGGjBvsvgmdSjnnzVwbcmuFeZtvKOMK+dI5TytdAoLtXTTMz7778xjPiNMrCxHRjc7T84F2687LN4IfijqzCEYUsGkoby+DNjUs+dN0lhGKMuFVk8E+UXe64F9vep6kFy4+2GBOHsKCd4ZHVkaGDKh9hp5xfmnf/gOnkbEO3kqmI8y9jZh0MPOX2aCS47Le3mhcpxir42Mlnxjzi8b1brgytUmj/334G3l2d+F+vZeCskOOkrmglUb588diQmHOXMou36xBFhtXXD6cyBCe0BqES5ehLoudnMaP1Rnu/vRmT27MHfgAzEapACpVdL6YYgedm4Ft5FaBlDbfXGuG5A2snKop7wwqPK4Fn/hftgLxZZn0T/COWQlxybuo7OollultpMmUe7JOILAb2WjH7/Hl1pXm+bP3MPydeyCMfTJOHCf/m+vztaGC6M5wMFbw878HqVDzYO8yuHFLUd473V9vGCdSZwaWSxUxueOsjR6Yq5mSnA/a85KrqUMnHc0QopSi2jMqrG+2+6FSmuMOn/IHn3ZacZCwYxO3P3hiEAndJUQ07cquOtIY9CLkx3ziTP6cydDPcLQa01PSmKTWzJIqb/YT6v2GQ56E82UolOylplCdHcehMeAWmIGXsUsxvEEKXhFbpjE3VZCSvcTi9Ws2c90qLE+6iyu3wtWJQCtYL/2sSrv9IuKlxCCTAfQNRbr6D+JNOAsMEkXSxBpvfSg5NXw4AJKS6rIwvpkV5iG6pbaF9hfCwsXlspRt9gdc5ggpTvNtriS0dpLfy3CTx3DX24/mHVJI5anETxeB0w5+bgIBNjoP29ICUohtaZ9NgES57xpjxkdbbHuqd /i5SxpAc mIH9dgjxd5ihpZPWZ984uB1O/qM5Zjop1ZayRIBbBLfC0pjG6NVKgzzZ/JcUG/zUI4MmA7Esc6VPBr87JirjfVkpZwefimT+4v0pfA+UP9cVElQLARlnlihKjnvkGOhkwqEHHI3aVnrkfXjXN/xsWrQxQD5NlkpjykgxQw+6M0L71SEWU4QFIp+9xK+HJ/JTwlg9/jC89AAWciRhfD7Sl1Q8cDw== 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: On 15/10/2025 18:52, Dave Hansen wrote: > On 10/15/25 01:27, Kevin Brodsky wrote: >> While at it, we can also avoid preempt_disable() if we are not >> in lazy MMU mode - xen_get_lazy_mode() should tolerate preemption. > ... >> static void xen_flush_lazy_mmu(void) >> { >> - preempt_disable(); >> - >> if (xen_get_lazy_mode() == XEN_LAZY_MMU) { >> - arch_leave_lazy_mmu_mode(); >> - arch_enter_lazy_mmu_mode(); >> + preempt_disable(); >> + xen_mc_flush(); >> + preempt_enable(); >> } > But xen_get_lazy_mode() does: > > this_cpu_read(xen_lazy_mode); > > Couldn't preemption end up doing the 'xen_lazy_mode' read and the > xen_mc_flush() on different CPUs? > > That seems like a problem. Is there a reason it's safe? You're right, I was thinking in terms of task, but xen_mc_flush() does operate on the current CPU (and it's called when context-switching). Will restore the original order in v4. - Kevin