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 4452DC46467 for ; Thu, 14 Apr 2022 15:17:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346616AbiDNPPB (ORCPT ); Thu, 14 Apr 2022 11:15:01 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45536 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1347214AbiDNN6g (ORCPT ); Thu, 14 Apr 2022 09:58:36 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A4779B82C1; Thu, 14 Apr 2022 06:49:11 -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 ams.source.kernel.org (Postfix) with ESMTPS id 4DBFBB82894; Thu, 14 Apr 2022 13:49:10 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9445FC385A1; Thu, 14 Apr 2022 13:49:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1649944149; bh=cBqeMbl+UOPWrgSvxQeVCurOeOpmkuHKlzDZEIm6juw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=TXmKDCVC+0kyt5PW+J00PcvUDQ30B7b45RQ194W+gZRwHXTnrmTT2KtnEvoogX8sf i1avT9MWdmAmwZsxlgxczBsDFGTAfzV2wUx1RljqIBItnQySuoTwhwZrjgsSoCn9GW RAWgtCFj3LjMDqJplfbOrDm+PfNR1nylVfK+xWIw= 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 5.4 411/475] xen: delay xen_hvm_init_time_ops() if kdump is boot on vcpu>=32 Date: Thu, 14 Apr 2022 15:13:16 +0200 Message-Id: <20220414110906.566683136@linuxfoundation.org> X-Mailer: git-send-email 2.35.2 In-Reply-To: <20220414110855.141582785@linuxfoundation.org> References: <20220414110855.141582785@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: linux-kernel@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 f8d39440b292..e5bd9eb42191 100644 --- a/arch/x86/xen/smp_hvm.c +++ b/arch/x86/xen/smp_hvm.c @@ -18,6 +18,12 @@ 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 befbdd8b17f0..4ec6c80f7687 100644 --- a/arch/x86/xen/time.c +++ b/arch/x86/xen/time.c @@ -547,6 +547,11 @@ 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 @@ -556,7 +561,22 @@ 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; } @@ -568,6 +588,8 @@ 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