From patchwork Mon Mar 3 14:15:39 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ryan Roberts X-Patchwork-Id: 13998906 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]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4CA72C282D2 for ; Mon, 3 Mar 2025 14:16:11 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 593066B008C; Mon, 3 Mar 2025 09:16:09 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 542C4280001; Mon, 3 Mar 2025 09:16:09 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3BE666B0092; Mon, 3 Mar 2025 09:16:09 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 04EAA280002 for ; Mon, 3 Mar 2025 09:16:08 -0500 (EST) Received: from smtpin29.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id AD325A4298 for ; Mon, 3 Mar 2025 14:16:08 +0000 (UTC) X-FDA: 83180439216.29.C1CF372 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf04.hostedemail.com (Postfix) with ESMTP id F04BD40007 for ; Mon, 3 Mar 2025 14:16:06 +0000 (UTC) Authentication-Results: imf04.hostedemail.com; dkim=none; spf=pass (imf04.hostedemail.com: domain of ryan.roberts@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=ryan.roberts@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=1741011367; 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=FkznIVejyRN2Si5st8BW1VC5w3S2Z+0ceo2AEitunJI=; b=T12Rg6mUMgo0uR00uycu711EGhKcuLntShhwGSh4Bg6Mq2OolPlvvfp+ITfRsPZmKCNnn0 BQsAhyXkxDS7KIoptP+K50CI8+ZcpSANjRJZQvYq4A6zZ6a9DRIynKVjJ5KoRxAJFpLgUJ wkDa1TuE46Q3pFLEDXIbnFk8Go0Wrh4= ARC-Authentication-Results: i=1; imf04.hostedemail.com; dkim=none; spf=pass (imf04.hostedemail.com: domain of ryan.roberts@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=ryan.roberts@arm.com; dmarc=pass (policy=none) header.from=arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1741011367; a=rsa-sha256; cv=none; b=0HjE6IOI2KRUonxcX40exyR1A/qw1Kh9+/03AmhNregZ4xhfV9AtJHwUOCC4jz7Ltlcai7 HMHR6Qlt6+TyRHhZLQvVf1wzxtwFA8IB6z4X2vJlWLrN3pOZ5I+hVKjuNnu8tIzYWNXjJu jEhwPYr3fT4Pw0t8/QQKPr9O3tCnSYw= 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 4F7BE106F; Mon, 3 Mar 2025 06:16:20 -0800 (PST) Received: from e125769.cambridge.arm.com (e125769.cambridge.arm.com [10.1.196.27]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2C3CA3F66E; Mon, 3 Mar 2025 06:16:04 -0800 (PST) From: Ryan Roberts To: Andrew Morton , "David S. Miller" , Andreas Larsson , Juergen Gross , Boris Ostrovsky , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , "Matthew Wilcox (Oracle)" , Catalin Marinas Cc: Ryan Roberts , linux-mm@kvack.org, sparclinux@vger.kernel.org, xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, David Hildenbrand Subject: [PATCH v2 5/5] Revert "x86/xen: allow nesting of same lazy mode" Date: Mon, 3 Mar 2025 14:15:39 +0000 Message-ID: <20250303141542.3371656-6-ryan.roberts@arm.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20250303141542.3371656-1-ryan.roberts@arm.com> References: <20250303141542.3371656-1-ryan.roberts@arm.com> MIME-Version: 1.0 X-Rspam-User: X-Stat-Signature: 45aqkq4w4kzshqnsdnysmparjxirppeb X-Rspamd-Queue-Id: F04BD40007 X-Rspamd-Server: rspam07 X-HE-Tag: 1741011366-166355 X-HE-Meta: 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 Ec9aoJzT RWb5cVB9xkJDn/YxdixFw8LCRtQpHI/1zK9DjadD8SKXH/mZwCNs9RFJnQPYm4Uaxwlua/QJFMZY5IulkkIqf46Q0hv2w9E5a7E0KHhOB9EjTz9Nnk1RV9Ft1yKhCH2I337EcK6Hj/A1inmPEQwXWvkY+2nwLTqn2ERbmq4zOo+HX3sMxxA7gDSSL1g== 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: Commit 49147beb0ccb ("x86/xen: allow nesting of same lazy mode") was added as a solution for a core-mm code change where arch_[enter|leave]_lazy_mmu_mode() started to be called in a nested manner; see commit bcc6cc832573 ("mm: add default definition of set_ptes()"). However, now that we have fixed the API to avoid nesting, we no longer need this capability in the x86 implementation. Additionally, from code review, I don't believe the fix was ever robust in the case of preemption occurring while in the nested lazy mode. The implementation usually deals with preemption by calling arch_leave_lazy_mmu_mode() from xen_start_context_switch() for the outgoing task if we are in the lazy mmu mode. Then in xen_end_context_switch(), it restarts the lazy mode by calling arch_enter_lazy_mmu_mode() for an incoming task that was in the lazy mode when it was switched out. But arch_leave_lazy_mmu_mode() will only unwind a single level of nesting. If we are in the double nest, then it's not fully unwound and per-cpu variables are left in a bad state. So the correct solution is to remove the possibility of nesting from the higher level (which has now been done) and remove this x86-specific solution. Acked-by: David Hildenbrand Signed-off-by: Ryan Roberts --- arch/x86/include/asm/xen/hypervisor.h | 15 ++------------- arch/x86/xen/enlighten_pv.c | 1 - 2 files changed, 2 insertions(+), 14 deletions(-) diff --git a/arch/x86/include/asm/xen/hypervisor.h b/arch/x86/include/asm/xen/hypervisor.h index a9088250770f..bd0fc69a10a7 100644 --- a/arch/x86/include/asm/xen/hypervisor.h +++ b/arch/x86/include/asm/xen/hypervisor.h @@ -72,18 +72,10 @@ enum xen_lazy_mode { }; DECLARE_PER_CPU(enum xen_lazy_mode, xen_lazy_mode); -DECLARE_PER_CPU(unsigned int, xen_lazy_nesting); static inline void enter_lazy(enum xen_lazy_mode mode) { - enum xen_lazy_mode old_mode = this_cpu_read(xen_lazy_mode); - - if (mode == old_mode) { - this_cpu_inc(xen_lazy_nesting); - return; - } - - BUG_ON(old_mode != XEN_LAZY_NONE); + BUG_ON(this_cpu_read(xen_lazy_mode) != XEN_LAZY_NONE); this_cpu_write(xen_lazy_mode, mode); } @@ -92,10 +84,7 @@ static inline void leave_lazy(enum xen_lazy_mode mode) { BUG_ON(this_cpu_read(xen_lazy_mode) != mode); - if (this_cpu_read(xen_lazy_nesting) == 0) - this_cpu_write(xen_lazy_mode, XEN_LAZY_NONE); - else - this_cpu_dec(xen_lazy_nesting); + this_cpu_write(xen_lazy_mode, XEN_LAZY_NONE); } enum xen_lazy_mode xen_get_lazy_mode(void); diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c index 5e57835e999d..919e4df9380b 100644 --- a/arch/x86/xen/enlighten_pv.c +++ b/arch/x86/xen/enlighten_pv.c @@ -99,7 +99,6 @@ struct tls_descs { }; DEFINE_PER_CPU(enum xen_lazy_mode, xen_lazy_mode) = XEN_LAZY_NONE; -DEFINE_PER_CPU(unsigned int, xen_lazy_nesting); enum xen_lazy_mode xen_get_lazy_mode(void) {