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bh=gZipOVj0ANJPBHydjW1hu0Ub3HQQYNC8CTUA2epZ4yg=; b=rq/waDtXqD83I1LO13s/dAe4rfd2+WEYrqAIA+MfrfPXjYA0GVcXf9tmalQjqZtT8FZ9hNqyMAZ7qEXUNE2pPDs37wD22SyTeyAA9DgvUZSI4C4kckszH6AkXEKKNYIjGaO1Z1oWQLKso0s2hsW91CpHENHa9r04OEhq1UR5XRM= From: Dongli Zhang To: xen-devel@lists.xenproject.org, x86@kernel.org Cc: linux-kernel@vger.kernel.org, boris.ostrovsky@oracle.com, jgross@suse.com, sstabellini@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, joe.jin@oracle.com Subject: [PATCH v3 1/1] xen: delay xen_hvm_init_time_ops() to xen_hvm_smp_prepare_boot_cpu() Date: Thu, 24 Feb 2022 13:50:49 -0800 Message-Id: <20220224215049.2845-2-dongli.zhang@oracle.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20220224215049.2845-1-dongli.zhang@oracle.com> References: <20220224215049.2845-1-dongli.zhang@oracle.com> X-ClientProxiedBy: SA9PR13CA0099.namprd13.prod.outlook.com (2603:10b6:806:24::14) To BYAPR10MB2663.namprd10.prod.outlook.com (2603:10b6:a02:a9::20) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: e8445e2c-1374-4bf2-db86-08d9f7dfc2df X-MS-TrafficTypeDiagnostic: BN6PR10MB2020:EE_ X-Microsoft-Antispam-PRVS: X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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charset="utf-8" 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 =3D xen_hvm_guest_init() -> xen_hvm_init_time_ops() -> xen_clocksource_read() -> src =3D &__this_cpu_read(xen_vcpu)->time; This is because Xen HVM supports at most MAX_VIRT_CPUS=3D32 '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 >=3D 32, since xen_vcpu_info_reset(0) would set per_cpu(xen_vcpu, cpu) =3D NULL when vcpu >=3D 32, xen_clocksource_read() on vcpu >=3D 32 would panic. This patch always delays xen_hvm_init_time_ops() to later in xen_hvm_smp_prepare_boot_cpu() after the 'vcpu_info' for boot vcpu is registered. 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" Unfortunately, the 'soft_reset' (kexec) does not work with mainline xen version so that I can test this patch only with HVM guest on old xen hypervisor where 'soft_reset' is working. The bugfix for PVM is not implemented due to the lack of testing environment. Cc: Joe Jin Signed-off-by: Dongli Zhang --- Changed since v1: - Add commit message to explain why xen_hvm_init_time_ops() is delayed for any vcpus. (Suggested by Boris Ostrovsky) - Add a comment in xen_hvm_smp_prepare_boot_cpu() referencing the related code in xen_hvm_guest_init(). (suggested by Juergen Gross) Changed since v2: - Delay for all VCPUs. (Suggested by Boris Ostrovsky) - Add commit message that why PVM is not supported by this patch - Test if kexec/kdump works with mainline xen (HVM and PVM) arch/x86/xen/enlighten_hvm.c | 1 - arch/x86/xen/smp_hvm.c | 17 +++++++++++++++++ 2 files changed, 17 insertions(+), 1 deletion(-) diff --git a/arch/x86/xen/enlighten_hvm.c b/arch/x86/xen/enlighten_hvm.c index 517a9d8d8f94..53f306ec1d3b 100644 --- a/arch/x86/xen/enlighten_hvm.c +++ b/arch/x86/xen/enlighten_hvm.c @@ -216,7 +216,6 @@ static void __init xen_hvm_guest_init(void) WARN_ON(xen_cpuhp_setup(xen_cpu_up_prepare_hvm, xen_cpu_dead_hvm)); xen_unplug_emulated_devices(); x86_init.irqs.intr_init =3D xen_init_IRQ; - xen_hvm_init_time_ops(); xen_hvm_init_mmu_ops(); =20 #ifdef CONFIG_KEXEC_CORE diff --git a/arch/x86/xen/smp_hvm.c b/arch/x86/xen/smp_hvm.c index 6ff3c887e0b9..9a5efc1a1633 100644 --- a/arch/x86/xen/smp_hvm.c +++ b/arch/x86/xen/smp_hvm.c @@ -19,6 +19,23 @@ static void __init xen_hvm_smp_prepare_boot_cpu(void) */ xen_vcpu_setup(0); =20 + /* + * xen_hvm_init_time_ops() used to be called at very early stage + * by xen_hvm_guest_init(). While only MAX_VIRT_CPUS 'vcpu_info' + * are embedded inside 'shared_info', the VM would use them until + * xen_vcpu_setup() is used to allocate/relocate them at arbitrary + * address. + * + * However, when Xen HVM guest boots on vcpu >=3D MAX_VIRT_CPUS + * (e.g., kexec kernel), per_cpu(xen_vcpu, cpu) is NULL at early + * stage. To access per_cpu(xen_vcpu, cpu) via + * xen_clocksource_read() would panic the kernel. + * + * Therefore we always delay xen_hvm_init_time_ops() to + * xen_hvm_smp_prepare_boot_cpu() to avoid the panic. + */ + 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 --=20 2.17.1