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 972C1CA1013 for ; Mon, 8 Sep 2025 07:32:23 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 91A088E0005; Mon, 8 Sep 2025 03:32:22 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 8CA728E0001; Mon, 8 Sep 2025 03:32:22 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 7E03F8E0005; Mon, 8 Sep 2025 03:32:22 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 6D0198E0001 for ; Mon, 8 Sep 2025 03:32:22 -0400 (EDT) Received: from smtpin24.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 13F2BBC741 for ; Mon, 8 Sep 2025 07:32:22 +0000 (UTC) X-FDA: 83865264924.24.1607EAF Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf09.hostedemail.com (Postfix) with ESMTP id D664514000A for ; Mon, 8 Sep 2025 07:32:19 +0000 (UTC) Authentication-Results: imf09.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf09.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=1757316740; 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=FTbsn9ueX//BY69AI+6lqPyl2zCJvGI1tcc+SkL1r0Q=; b=PTjGys/gjkxUEE33t65EEQAWPyBtcEQg09QLkOVt2CydG/AWrfKrR9J3myGKudLg1Cs5Z6 Uw8C3BAn310R5Sx6duujGCyIhRILRKlPjEGyJgW+JMh0dfXrnrTiA3zJYOVaSzyRm/rcXy UFSAMFBCKCQcWBc3aXE3modxK6K5Fuw= ARC-Authentication-Results: i=1; imf09.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf09.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=1757316740; a=rsa-sha256; cv=none; b=T2k7KvnIOTUk5WaCvzgzulbGLqearDa8d8mE8ETln4wKKS7xeszO0JCnUVBwGfU6lIOUbH 328yShTnN5CoN94IxHGtjz0KKBp2kGjiYiqRXez8dHoGseBHmrSlshyeE26wL9D40+L1f/ 6FMGKCPWmPIBx63T1trpvqaPsORjB1g= 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 4F1201692; Mon, 8 Sep 2025 00:32:10 -0700 (PDT) Received: from [10.57.58.69] (unknown [10.57.58.69]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 5A2713F63F; Mon, 8 Sep 2025 00:32:12 -0700 (PDT) Message-ID: <16a63f8a-fe9f-4a65-be45-7260858734bd@arm.com> Date: Mon, 8 Sep 2025 09:32:09 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 4/7] x86/xen: support nested lazy_mmu sections (again) To: Alexander Gordeev Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, 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 References: <20250904125736.3918646-1-kevin.brodsky@arm.com> <20250904125736.3918646-5-kevin.brodsky@arm.com> Content-Language: en-GB From: Kevin Brodsky In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: D664514000A X-Stat-Signature: tczzi9gnyqwwzman41ryeakccdxf8diy X-Rspam-User: X-HE-Tag: 1757316739-21726 X-HE-Meta: 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 6+xaZS+l 9Vl2TltyE2VCBnnkUNdBw221Wg4kGD3NgZWdI4gd400a0ZDx9fLD88fFCOrzpBWrGR/Fk8ThftyekJ7DvYR0L0arZen1HiJnQVvAWJkD3QWHdWtdytSGq0nyZUYBhwKpNmZAd4vZf+or5zvJzJgQmjbs1e3X5jDrQRsReYxDAJI3FG5kz5oIZmd3ClyZog/kJx31V 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 05/09/2025 17:48, Alexander Gordeev wrote: > On Thu, Sep 04, 2025 at 01:57:33PM +0100, Kevin Brodsky wrote: > ... >> -static void xen_enter_lazy_mmu(void) >> +static lazy_mmu_state_t xen_enter_lazy_mmu(void) >> { >> + if (this_cpu_read(xen_lazy_mode) == XEN_LAZY_MMU) >> + return LAZY_MMU_NESTED; >> + >> enter_lazy(XEN_LAZY_MMU); >> + return LAZY_MMU_DEFAULT; >> } >> >> static void xen_flush_lazy_mmu(void) >> @@ -2167,11 +2171,12 @@ static void __init xen_post_allocator_init(void) >> pv_ops.mmu.write_cr3 = &xen_write_cr3; >> } >> >> -static void xen_leave_lazy_mmu(void) >> +static void xen_leave_lazy_mmu(lazy_mmu_state_t state) >> { >> preempt_disable(); >> xen_mc_flush(); >> - leave_lazy(XEN_LAZY_MMU); >> + if (state != LAZY_MMU_NESTED) >> + leave_lazy(XEN_LAZY_MMU); > Based on xen_enter_lazy_mmu(), whether this condition needs to be > executed with the preemption disabled? AFAIU xen_mc_flush() needs preemption to be disabled. I don't think {enter,leave}_lazy() do, but this patch doesn't introduce any change from that perspective. I suppose it doesn't hurt that xen_leave_lazy_mmu() calls leave_lazy() with preemption disabled. > Or may be this_cpu_read(xen_lazy_mode) + enter_lazy(XEN_LAZY_MMU) > should be executed with the preemption disabled? Adding another this_cpu_read(xen_lazy_mode) in xen_enter_lazy_mmu() shouldn't change the situation, i.e. preemption should still be safe. If preemption occurs in the middle of that function, xen_{start,end}_context_switch() will do the right thing to save/restore xen_lazy_mode. - Kevin