diff options
Diffstat (limited to 'arch/x86/kernel/reboot.c')
| -rw-r--r-- | arch/x86/kernel/reboot.c | 162 |
1 files changed, 125 insertions, 37 deletions
diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c index c3636ea4aa71..964f6b0a3d68 100644 --- a/arch/x86/kernel/reboot.c +++ b/arch/x86/kernel/reboot.c @@ -12,6 +12,7 @@ #include <linux/delay.h> #include <linux/objtool.h> #include <linux/pgtable.h> +#include <linux/kexec.h> #include <acpi/reboot.h> #include <asm/io.h> #include <asm/apic.h> @@ -22,7 +23,6 @@ #include <asm/reboot_fixups.h> #include <asm/reboot.h> #include <asm/pci_x86.h> -#include <asm/virtext.h> #include <asm/cpu.h> #include <asm/nmi.h> #include <asm/smp.h> @@ -528,36 +528,79 @@ static inline void kb_wait(void) } } -static void vmxoff_nmi(int cpu, struct pt_regs *regs) +static inline void nmi_shootdown_cpus_on_restart(void); + +#if IS_ENABLED(CONFIG_KVM_X86) +/* RCU-protected callback to disable virtualization prior to reboot. */ +static cpu_emergency_virt_cb __rcu *cpu_emergency_virt_callback; + +void cpu_emergency_register_virt_callback(cpu_emergency_virt_cb *callback) { - cpu_emergency_vmxoff(); + if (WARN_ON_ONCE(rcu_access_pointer(cpu_emergency_virt_callback))) + return; + + rcu_assign_pointer(cpu_emergency_virt_callback, callback); } +EXPORT_SYMBOL_GPL(cpu_emergency_register_virt_callback); -/* Use NMIs as IPIs to tell all CPUs to disable virtualization */ -static void emergency_vmx_disable_all(void) +void cpu_emergency_unregister_virt_callback(cpu_emergency_virt_cb *callback) +{ + if (WARN_ON_ONCE(rcu_access_pointer(cpu_emergency_virt_callback) != callback)) + return; + + rcu_assign_pointer(cpu_emergency_virt_callback, NULL); + synchronize_rcu(); +} +EXPORT_SYMBOL_GPL(cpu_emergency_unregister_virt_callback); + +/* + * Disable virtualization, i.e. VMX or SVM, to ensure INIT is recognized during + * reboot. VMX blocks INIT if the CPU is post-VMXON, and SVM blocks INIT if + * GIF=0, i.e. if the crash occurred between CLGI and STGI. + */ +void cpu_emergency_disable_virtualization(void) +{ + cpu_emergency_virt_cb *callback; + + /* + * IRQs must be disabled as KVM enables virtualization in hardware via + * function call IPIs, i.e. IRQs need to be disabled to guarantee + * virtualization stays disabled. + */ + lockdep_assert_irqs_disabled(); + + rcu_read_lock(); + callback = rcu_dereference(cpu_emergency_virt_callback); + if (callback) + callback(); + rcu_read_unlock(); +} + +static void emergency_reboot_disable_virtualization(void) { - /* Just make sure we won't change CPUs while doing this */ local_irq_disable(); /* - * Disable VMX on all CPUs before rebooting, otherwise we risk hanging - * the machine, because the CPU blocks INIT when it's in VMX root. + * Disable virtualization on all CPUs before rebooting to avoid hanging + * the system, as VMX and SVM block INIT when running in the host. * * We can't take any locks and we may be on an inconsistent state, so - * use NMIs as IPIs to tell the other CPUs to exit VMX root and halt. + * use NMIs as IPIs to tell the other CPUs to disable VMX/SVM and halt. * - * Do the NMI shootdown even if VMX if off on _this_ CPU, as that - * doesn't prevent a different CPU from being in VMX root operation. + * Do the NMI shootdown even if virtualization is off on _this_ CPU, as + * other CPUs may have virtualization enabled. */ - if (cpu_has_vmx()) { - /* Safely force _this_ CPU out of VMX root operation. */ - __cpu_emergency_vmxoff(); + if (rcu_access_pointer(cpu_emergency_virt_callback)) { + /* Safely force _this_ CPU out of VMX/SVM operation. */ + cpu_emergency_disable_virtualization(); - /* Halt and exit VMX root operation on the other CPUs. */ - nmi_shootdown_cpus(vmxoff_nmi); + /* Disable VMX/SVM and halt on other CPUs. */ + nmi_shootdown_cpus_on_restart(); } } - +#else +static void emergency_reboot_disable_virtualization(void) { } +#endif /* CONFIG_KVM_X86 */ void __attribute__((weak)) mach_reboot_fixups(void) { @@ -590,7 +633,7 @@ static void native_machine_emergency_restart(void) unsigned short mode; if (reboot_emergency) - emergency_vmx_disable_all(); + emergency_reboot_disable_virtualization(); tboot_shutdown(TB_SHUTDOWN_REBOOT); @@ -674,6 +717,14 @@ static void native_machine_emergency_restart(void) void native_machine_shutdown(void) { + /* + * Call enc_kexec_begin() while all CPUs are still active and + * interrupts are enabled. This will allow all in-flight memory + * conversions to finish cleanly. + */ + if (kexec_in_progress) + x86_platform.guest.enc_kexec_begin(); + /* Stop the cpus and apics */ #ifdef CONFIG_X86_IO_APIC /* @@ -710,6 +761,9 @@ void native_machine_shutdown(void) #ifdef CONFIG_X86_64 x86_platform.iommu_shutdown(); #endif + + if (kexec_in_progress) + x86_platform.guest.enc_kexec_finish(); } static void __machine_emergency_restart(int emergency) @@ -754,7 +808,7 @@ struct machine_ops machine_ops __ro_after_init = { .emergency_restart = native_machine_emergency_restart, .restart = native_machine_restart, .halt = native_machine_halt, -#ifdef CONFIG_KEXEC_CORE +#ifdef CONFIG_CRASH_DUMP .crash_shutdown = native_machine_crash_shutdown, #endif }; @@ -784,14 +838,13 @@ void machine_halt(void) machine_ops.halt(); } -#ifdef CONFIG_KEXEC_CORE +#ifdef CONFIG_CRASH_DUMP void machine_crash_shutdown(struct pt_regs *regs) { machine_ops.crash_shutdown(regs); } #endif - /* This is the CPU performing the emergency shutdown work. */ int crashing_cpu = -1; @@ -817,9 +870,22 @@ static int crash_nmi_callback(unsigned int val, struct pt_regs *regs) return NMI_HANDLED; local_irq_disable(); - shootdown_callback(cpu, regs); + if (shootdown_callback) + shootdown_callback(cpu, regs); + + /* + * Prepare the CPU for reboot _after_ invoking the callback so that the + * callback can safely use virtualization instructions, e.g. VMCLEAR. + */ + cpu_emergency_disable_virtualization(); atomic_dec(&waiting_for_crash_ipi); + + if (smp_ops.stop_this_cpu) { + smp_ops.stop_this_cpu(); + BUG(); + } + /* Assume hlt works */ halt(); for (;;) @@ -828,33 +894,43 @@ static int crash_nmi_callback(unsigned int val, struct pt_regs *regs) return NMI_HANDLED; } -/* - * Halt all other CPUs, calling the specified function on each of them +/** + * nmi_shootdown_cpus - Stop other CPUs via NMI + * @callback: Optional callback to be invoked from the NMI handler * - * This function can be used to halt all other CPUs on crash - * or emergency reboot time. The function passed as parameter - * will be called inside a NMI handler on all CPUs. + * The NMI handler on the remote CPUs invokes @callback, if not + * NULL, first and then disables virtualization to ensure that + * INIT is recognized during reboot. + * + * nmi_shootdown_cpus() can only be invoked once. After the first + * invocation all other CPUs are stuck in crash_nmi_callback() and + * cannot respond to a second NMI. */ void nmi_shootdown_cpus(nmi_shootdown_cb callback) { unsigned long msecs; + local_irq_disable(); + /* + * Avoid certain doom if a shootdown already occurred; re-registering + * the NMI handler will cause list corruption, modifying the callback + * will do who knows what, etc... + */ + if (WARN_ON_ONCE(crash_ipi_issued)) + return; + /* Make a note of crashing cpu. Will be used in NMI callback. */ - crashing_cpu = safe_smp_processor_id(); + crashing_cpu = smp_processor_id(); shootdown_callback = callback; atomic_set(&waiting_for_crash_ipi, num_online_cpus() - 1); - /* Would it be better to replace the trap vector here? */ - if (register_nmi_handler(NMI_LOCAL, crash_nmi_callback, - NMI_FLAG_FIRST, "crash")) - return; /* Return what? */ + /* - * Ensure the new callback function is set before sending - * out the NMI + * Set emergency handler to preempt other handlers. */ - wmb(); + set_emergency_nmi_handler(NMI_LOCAL, crash_nmi_callback); apic_send_IPI_allbutself(NMI_VECTOR); @@ -867,7 +943,17 @@ void nmi_shootdown_cpus(nmi_shootdown_cb callback) msecs--; } - /* Leave the nmi callback set */ + /* + * Leave the nmi callback set, shootdown is a one-time thing. Clearing + * the callback could result in a NULL pointer dereference if a CPU + * (finally) responds after the timeout expires. + */ +} + +static inline void nmi_shootdown_cpus_on_restart(void) +{ + if (!crash_ipi_issued) + nmi_shootdown_cpus(NULL); } /* @@ -882,7 +968,7 @@ void run_crash_ipi_callback(struct pt_regs *regs) } /* Override the weak function in kernel/panic.c */ -void nmi_panic_self_stop(struct pt_regs *regs) +void __noreturn nmi_panic_self_stop(struct pt_regs *regs) { while (1) { /* If no CPU is preparing crash dump, we simply loop here. */ @@ -897,6 +983,8 @@ void nmi_shootdown_cpus(nmi_shootdown_cb callback) /* No other CPUs to shoot down */ } +static inline void nmi_shootdown_cpus_on_restart(void) { } + void run_crash_ipi_callback(struct pt_regs *regs) { } |