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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A08C3C433EF for ; Tue, 12 Apr 2022 06:44:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1350586AbiDLGqi (ORCPT ); Tue, 12 Apr 2022 02:46:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40048 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1351517AbiDLGo7 (ORCPT ); Tue, 12 Apr 2022 02:44:59 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D075E3B016; Mon, 11 Apr 2022 23:38:29 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 648DD61890; Tue, 12 Apr 2022 06:38:29 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 710DDC385AA; Tue, 12 Apr 2022 06:38:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1649745508; bh=dS4Ec1ETEUy0L3oe3+/4Q2mGmFJR4XF03TO6xAu2qz0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=kTiNRc37DLdsN8eLaSs78h0avpvhrNT/C7M8pI9QlOYqtNYQV97KH4/a8773UIqau PC6e4tKIFKIXSvPjb8FdeDDbBzhg64VYyGJFuTZADP9iWUtcqVrEF9NDz8cs4Lvrp+ zeHuLtOcv3FUPCQK3W0goCJRFVVVU+CY1sJSvv8A= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Joe Jin , Dongli Zhang , Boris Ostrovsky , Sasha Levin Subject: [PATCH 5.10 079/171] xen: delay xen_hvm_init_time_ops() if kdump is boot on vcpu>=32 Date: Tue, 12 Apr 2022 08:29:30 +0200 Message-Id: <20220412062930.171908307@linuxfoundation.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220412062927.870347203@linuxfoundation.org> References: <20220412062927.870347203@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Dongli Zhang [ Upstream commit eed05744322da07dd7e419432dcedf3c2e017179 ] The sched_clock() can be used very early since commit 857baa87b642 ("sched/clock: Enable sched clock early"). In addition, with commit 38669ba205d1 ("x86/xen/time: Output xen sched_clock time from 0"), kdump kernel in Xen HVM guest may panic at very early stage when accessing &__this_cpu_read(xen_vcpu)->time as in below: setup_arch() -> init_hypervisor_platform() -> x86_init.hyper.init_platform = xen_hvm_guest_init() -> xen_hvm_init_time_ops() -> xen_clocksource_read() -> src = &__this_cpu_read(xen_vcpu)->time; This is because Xen HVM supports at most MAX_VIRT_CPUS=32 'vcpu_info' embedded inside 'shared_info' during early stage until xen_vcpu_setup() is used to allocate/relocate 'vcpu_info' for boot cpu at arbitrary address. However, when Xen HVM guest panic on vcpu >= 32, since xen_vcpu_info_reset(0) would set per_cpu(xen_vcpu, cpu) = NULL when vcpu >= 32, xen_clocksource_read() on vcpu >= 32 would panic. This patch calls xen_hvm_init_time_ops() again later in xen_hvm_smp_prepare_boot_cpu() after the 'vcpu_info' for boot vcpu is registered when the boot vcpu is >= 32. This issue can be reproduced on purpose via below command at the guest side when kdump/kexec is enabled: "taskset -c 33 echo c > /proc/sysrq-trigger" The bugfix for PVM is not implemented due to the lack of testing environment. [boris: xen_hvm_init_time_ops() returns on errors instead of jumping to end] Cc: Joe Jin Signed-off-by: Dongli Zhang Reviewed-by: Boris Ostrovsky Link: https://lore.kernel.org/r/20220302164032.14569-3-dongli.zhang@oracle.com Signed-off-by: Boris Ostrovsky Signed-off-by: Sasha Levin --- arch/x86/xen/smp_hvm.c | 6 ++++++ arch/x86/xen/time.c | 24 +++++++++++++++++++++++- 2 files changed, 29 insertions(+), 1 deletion(-) diff --git a/arch/x86/xen/smp_hvm.c b/arch/x86/xen/smp_hvm.c index 6ff3c887e0b9..b70afdff419c 100644 --- a/arch/x86/xen/smp_hvm.c +++ b/arch/x86/xen/smp_hvm.c @@ -19,6 +19,12 @@ static void __init xen_hvm_smp_prepare_boot_cpu(void) */ xen_vcpu_setup(0); + /* + * Called again in case the kernel boots on vcpu >= MAX_VIRT_CPUS. + * Refer to comments in xen_hvm_init_time_ops(). + */ + xen_hvm_init_time_ops(); + /* * The alternative logic (which patches the unlock/lock) runs before * the smp bootup up code is activated. Hence we need to set this up diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c index 91f5b330dcc6..8183d17e1cf1 100644 --- a/arch/x86/xen/time.c +++ b/arch/x86/xen/time.c @@ -556,6 +556,11 @@ static void xen_hvm_setup_cpu_clockevents(void) void __init xen_hvm_init_time_ops(void) { + static bool hvm_time_initialized; + + if (hvm_time_initialized) + return; + /* * vector callback is needed otherwise we cannot receive interrupts * on cpu > 0 and at this point we don't know how many cpus are @@ -565,7 +570,22 @@ void __init xen_hvm_init_time_ops(void) return; if (!xen_feature(XENFEAT_hvm_safe_pvclock)) { - pr_info("Xen doesn't support pvclock on HVM, disable pv timer"); + pr_info_once("Xen doesn't support pvclock on HVM, disable pv timer"); + return; + } + + /* + * Only MAX_VIRT_CPUS 'vcpu_info' are embedded inside 'shared_info'. + * The __this_cpu_read(xen_vcpu) is still NULL when Xen HVM guest + * boots on vcpu >= MAX_VIRT_CPUS (e.g., kexec), To access + * __this_cpu_read(xen_vcpu) via xen_clocksource_read() will panic. + * + * The xen_hvm_init_time_ops() should be called again later after + * __this_cpu_read(xen_vcpu) is available. + */ + if (!__this_cpu_read(xen_vcpu)) { + pr_info("Delay xen_init_time_common() as kernel is running on vcpu=%d\n", + xen_vcpu_nr(0)); return; } @@ -577,6 +597,8 @@ void __init xen_hvm_init_time_ops(void) x86_platform.calibrate_tsc = xen_tsc_khz; x86_platform.get_wallclock = xen_get_wallclock; x86_platform.set_wallclock = xen_set_wallclock; + + hvm_time_initialized = true; } #endif -- 2.35.1