KVM: Rename and move CPUHP_AP_KVM_STARTING to ONLINE section

The CPU STARTING section doesn't allow callbacks to fail. Move KVM's
hotplug callback to ONLINE section so that it can abort onlining a CPU in
certain cases to avoid potentially breaking VMs running on existing CPUs.
For example, when KVM fails to enable hardware virtualization on the
hotplugged CPU.

Place KVM's hotplug state before CPUHP_AP_SCHED_WAIT_EMPTY as it ensures
when offlining a CPU, all user tasks and non-pinned kernel tasks have left
the CPU, i.e. there cannot be a vCPU task around. So, it is safe for KVM's
CPU offline callback to disable hardware virtualization at that point.
Likewise, KVM's online callback can enable hardware virtualization before
any vCPU task gets a chance to run on hotplugged CPUs.

Drop kvm_x86_check_processor_compatibility()'s WARN that IRQs are
disabled, as the ONLINE section runs with IRQs disabled.  The WARN wasn't
intended to be a requirement, e.g. disabling preemption is sufficient,
the IRQ thing was purely an aggressive sanity check since the helper was
only ever invoked via SMP function call.

Rename KVM's CPU hotplug callbacks accordingly.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Chao Gao <chao.gao@intel.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Reviewed-by: Yuan Yao <yuan.yao@intel.com>
[sean: drop WARN that IRQs are disabled]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20221130230934.1014142-42-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6f1cdc317de6410efcf942cafc97cf2cce00f7f9..1a262b60ec3f3113518108327f3c7ffb9deebd27 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9298,8 +9298,6 @@ static int kvm_x86_check_processor_compatibility(void)
 {
        struct cpuinfo_x86 *c = &cpu_data(smp_processor_id());
 
-       WARN_ON(!irqs_disabled());
-
        if (__cr4_reserved_bits(cpu_has, c) !=
            __cr4_reserved_bits(cpu_has, &boot_cpu_data))
                return -EIO;

diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
index 7337414e4947f5c43d45ca1b3679e0f727db760d..de45be38dd27f6925e276cd93466375bba7c639f 100644 (file)
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -185,7 +185,6 @@ enum cpuhp_state {
        CPUHP_AP_CSKY_TIMER_STARTING,
        CPUHP_AP_TI_GP_TIMER_STARTING,
        CPUHP_AP_HYPERV_TIMER_STARTING,
-       CPUHP_AP_KVM_STARTING,
        /* Must be the last timer callback */
        CPUHP_AP_DUMMY_TIMER_STARTING,
        CPUHP_AP_ARM_XEN_STARTING,
@@ -200,6 +199,7 @@ enum cpuhp_state {
 
        /* Online section invoked on the hotplugged CPU from the hotplug thread */
        CPUHP_AP_ONLINE_IDLE,
+       CPUHP_AP_KVM_ONLINE,
        CPUHP_AP_SCHED_WAIT_EMPTY,
        CPUHP_AP_SMPBOOT_THREADS,
        CPUHP_AP_X86_VDSO_VMA_ONLINE,

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index a07c8f7015ffccb143005ce4799418c0e5ff648b..b36df30d30f27523e03593af55155fac78d336f4 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -5082,13 +5082,27 @@ static void hardware_enable_nolock(void *junk)
        }
 }
 
-static int kvm_starting_cpu(unsigned int cpu)
+static int kvm_online_cpu(unsigned int cpu)
 {
+       int ret = 0;
+
+       /*
+        * Abort the CPU online process if hardware virtualization cannot
+        * be enabled. Otherwise running VMs would encounter unrecoverable
+        * errors when scheduled to this CPU.
+        */
        raw_spin_lock(&kvm_count_lock);
-       if (kvm_usage_count)
+       if (kvm_usage_count) {
+               WARN_ON_ONCE(atomic_read(&hardware_enable_failed));
+
                hardware_enable_nolock(NULL);
+               if (atomic_read(&hardware_enable_failed)) {
+                       atomic_set(&hardware_enable_failed, 0);
+                       ret = -EIO;
+               }
+       }
        raw_spin_unlock(&kvm_count_lock);
-       return 0;
+       return ret;
 }
 
 static void hardware_disable_nolock(void *junk)
@@ -5101,7 +5115,7 @@ static void hardware_disable_nolock(void *junk)
        kvm_arch_hardware_disable();
 }
 
-static int kvm_dying_cpu(unsigned int cpu)
+static int kvm_offline_cpu(unsigned int cpu)
 {
        raw_spin_lock(&kvm_count_lock);
        if (kvm_usage_count)
@@ -5878,8 +5892,8 @@ int kvm_init(unsigned vcpu_size, unsigned vcpu_align, struct module *module)
        if (!zalloc_cpumask_var(&cpus_hardware_enabled, GFP_KERNEL))
                return -ENOMEM;
 
-       r = cpuhp_setup_state_nocalls(CPUHP_AP_KVM_STARTING, "kvm/cpu:starting",
-                                     kvm_starting_cpu, kvm_dying_cpu);
+       r = cpuhp_setup_state_nocalls(CPUHP_AP_KVM_ONLINE, "kvm/cpu:online",
+                                     kvm_online_cpu, kvm_offline_cpu);
        if (r)
                goto out_free_2;
        register_reboot_notifier(&kvm_reboot_notifier);
@@ -5953,7 +5967,7 @@ out_free_4:
        kmem_cache_destroy(kvm_vcpu_cache);
 out_free_3:
        unregister_reboot_notifier(&kvm_reboot_notifier);
-       cpuhp_remove_state_nocalls(CPUHP_AP_KVM_STARTING);
+       cpuhp_remove_state_nocalls(CPUHP_AP_KVM_ONLINE);
 out_free_2:
        free_cpumask_var(cpus_hardware_enabled);
        return r;
@@ -5979,7 +5993,7 @@ void kvm_exit(void)
        kvm_async_pf_deinit();
        unregister_syscore_ops(&kvm_syscore_ops);
        unregister_reboot_notifier(&kvm_reboot_notifier);
-       cpuhp_remove_state_nocalls(CPUHP_AP_KVM_STARTING);
+       cpuhp_remove_state_nocalls(CPUHP_AP_KVM_ONLINE);
        on_each_cpu(hardware_disable_nolock, NULL, 1);
        kvm_irqfd_exit();
        free_cpumask_var(cpus_hardware_enabled);