6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Thomas Gleixner tglx@linutronix.de
commit 8f849ff63bcbc77670da03cb8f2b78b06257f455 upstream
Offline CPUs need to be parked in a safe loop when microcode update is in progress on the primary CPU. Currently, offline CPUs are parked in mwait_play_dead(), and for Intel CPUs, its not a safe instruction, because the MWAIT instruction can be patched in the new microcode update that can cause instability.
- Add a new microcode state 'UCODE_OFFLINE' to report status on per-CPU basis. - Force NMI on the offline CPUs.
Wake up offline CPUs while the update is in progress and then return them back to mwait_play_dead() after microcode update is complete.
Signed-off-by: Thomas Gleixner tglx@linutronix.de Signed-off-by: Borislav Petkov (AMD) bp@alien8.de Link: https://lore.kernel.org/r/20231002115903.660850472@linutronix.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/include/asm/microcode.h | 1 arch/x86/kernel/cpu/microcode/core.c | 112 +++++++++++++++++++++++++++++-- arch/x86/kernel/cpu/microcode/internal.h | 1 arch/x86/kernel/nmi.c | 5 + 4 files changed, 113 insertions(+), 6 deletions(-)
--- a/arch/x86/include/asm/microcode.h +++ b/arch/x86/include/asm/microcode.h @@ -71,6 +71,7 @@ static inline u32 intel_get_microcode_re #endif /* !CONFIG_CPU_SUP_INTEL */
bool microcode_nmi_handler(void); +void microcode_offline_nmi_handler(void);
#ifdef CONFIG_MICROCODE_LATE_LOADING DECLARE_STATIC_KEY_FALSE(microcode_nmi_handler_enable); --- a/arch/x86/kernel/cpu/microcode/core.c +++ b/arch/x86/kernel/cpu/microcode/core.c @@ -272,8 +272,9 @@ struct microcode_ctrl {
DEFINE_STATIC_KEY_FALSE(microcode_nmi_handler_enable); static DEFINE_PER_CPU(struct microcode_ctrl, ucode_ctrl); +static atomic_t late_cpus_in, offline_in_nmi; static unsigned int loops_per_usec; -static atomic_t late_cpus_in; +static cpumask_t cpu_offline_mask;
static noinstr bool wait_for_cpus(atomic_t *cnt) { @@ -381,7 +382,7 @@ static noinstr void load_secondary(unsig instrumentation_end(); }
-static void load_primary(unsigned int cpu) +static void __load_primary(unsigned int cpu) { struct cpumask *secondaries = topology_sibling_cpumask(cpu); enum sibling_ctrl ctrl; @@ -416,6 +417,67 @@ static void load_primary(unsigned int cp } }
+static bool kick_offline_cpus(unsigned int nr_offl) +{ + unsigned int cpu, timeout; + + for_each_cpu(cpu, &cpu_offline_mask) { + /* Enable the rendezvous handler and send NMI */ + per_cpu(ucode_ctrl.nmi_enabled, cpu) = true; + apic_send_nmi_to_offline_cpu(cpu); + } + + /* Wait for them to arrive */ + for (timeout = 0; timeout < (USEC_PER_SEC / 2); timeout++) { + if (atomic_read(&offline_in_nmi) == nr_offl) + return true; + udelay(1); + } + /* Let the others time out */ + return false; +} + +static void release_offline_cpus(void) +{ + unsigned int cpu; + + for_each_cpu(cpu, &cpu_offline_mask) + per_cpu(ucode_ctrl.ctrl, cpu) = SCTRL_DONE; +} + +static void load_primary(unsigned int cpu) +{ + unsigned int nr_offl = cpumask_weight(&cpu_offline_mask); + bool proceed = true; + + /* Kick soft-offlined SMT siblings if required */ + if (!cpu && nr_offl) + proceed = kick_offline_cpus(nr_offl); + + /* If the soft-offlined CPUs did not respond, abort */ + if (proceed) + __load_primary(cpu); + + /* Unconditionally release soft-offlined SMT siblings if required */ + if (!cpu && nr_offl) + release_offline_cpus(); +} + +/* + * Minimal stub rendezvous handler for soft-offlined CPUs which participate + * in the NMI rendezvous to protect against a concurrent NMI on affected + * CPUs. + */ +void noinstr microcode_offline_nmi_handler(void) +{ + if (!raw_cpu_read(ucode_ctrl.nmi_enabled)) + return; + raw_cpu_write(ucode_ctrl.nmi_enabled, false); + raw_cpu_write(ucode_ctrl.result, UCODE_OFFLINE); + raw_atomic_inc(&offline_in_nmi); + wait_for_ctrl(); +} + static noinstr bool microcode_update_handler(void) { unsigned int cpu = raw_smp_processor_id(); @@ -472,6 +534,7 @@ static int load_cpus_stopped(void *unuse static int load_late_stop_cpus(void) { unsigned int cpu, updated = 0, failed = 0, timedout = 0, siblings = 0; + unsigned int nr_offl, offline = 0; int old_rev = boot_cpu_data.microcode; struct cpuinfo_x86 prev_info;
@@ -479,6 +542,7 @@ static int load_late_stop_cpus(void) pr_err("You should switch to early loading, if possible.\n");
atomic_set(&late_cpus_in, num_online_cpus()); + atomic_set(&offline_in_nmi, 0); loops_per_usec = loops_per_jiffy / (TICK_NSEC / 1000);
/* @@ -501,6 +565,7 @@ static int load_late_stop_cpus(void) case UCODE_UPDATED: updated++; break; case UCODE_TIMEOUT: timedout++; break; case UCODE_OK: siblings++; break; + case UCODE_OFFLINE: offline++; break; default: failed++; break; } } @@ -512,6 +577,13 @@ static int load_late_stop_cpus(void) /* Nothing changed. */ if (!failed && !timedout) return 0; + + nr_offl = cpumask_weight(&cpu_offline_mask); + if (offline < nr_offl) { + pr_warn("%u offline siblings did not respond.\n", + nr_offl - atomic_read(&offline_in_nmi)); + return -EIO; + } pr_err("update failed: %u CPUs failed %u CPUs timed out\n", failed, timedout); return -EIO; @@ -545,19 +617,49 @@ static int load_late_stop_cpus(void) * modern CPUs uses MWAIT, which is also not guaranteed to be safe * against a microcode update which affects MWAIT. * - * 2) Initialize the per CPU control structure + * As soft-offlined CPUs still react on NMIs, the SMT sibling + * restriction can be lifted when the vendor driver signals to use NMI + * for rendezvous and the APIC provides a mechanism to send an NMI to a + * soft-offlined CPU. The soft-offlined CPUs are then able to + * participate in the rendezvous in a trivial stub handler. + * + * 2) Initialize the per CPU control structure and create a cpumask + * which contains "offline"; secondary threads, so they can be handled + * correctly by a control CPU. */ static bool setup_cpus(void) { struct microcode_ctrl ctrl = { .ctrl = SCTRL_WAIT, .result = -1, }; + bool allow_smt_offline; unsigned int cpu;
+ allow_smt_offline = microcode_ops->nmi_safe || + (microcode_ops->use_nmi && apic->nmi_to_offline_cpu); + + cpumask_clear(&cpu_offline_mask); + for_each_cpu_and(cpu, cpu_present_mask, &cpus_booted_once_mask) { + /* + * Offline CPUs sit in one of the play_dead() functions + * with interrupts disabled, but they still react on NMIs + * and execute arbitrary code. Also MWAIT being updated + * while the offline CPU sits there is not necessarily safe + * on all CPU variants. + * + * Mark them in the offline_cpus mask which will be handled + * by CPU0 later in the update process. + * + * Ensure that the primary thread is online so that it is + * guaranteed that all cores are updated. + */ if (!cpu_online(cpu)) { - if (topology_is_primary_thread(cpu) || !microcode_ops->nmi_safe) { - pr_err("CPU %u not online\n", cpu); + if (topology_is_primary_thread(cpu) || !allow_smt_offline) { + pr_err("CPU %u not online, loading aborted\n", cpu); return false; } + cpumask_set_cpu(cpu, &cpu_offline_mask); + per_cpu(ucode_ctrl, cpu) = ctrl; + continue; }
/* --- a/arch/x86/kernel/cpu/microcode/internal.h +++ b/arch/x86/kernel/cpu/microcode/internal.h @@ -17,6 +17,7 @@ enum ucode_state { UCODE_NFOUND, UCODE_ERROR, UCODE_TIMEOUT, + UCODE_OFFLINE, };
struct microcode_ops { --- a/arch/x86/kernel/nmi.c +++ b/arch/x86/kernel/nmi.c @@ -502,8 +502,11 @@ DEFINE_IDTENTRY_RAW(exc_nmi) if (IS_ENABLED(CONFIG_NMI_CHECK_CPU)) raw_atomic_long_inc(&nsp->idt_calls);
- if (IS_ENABLED(CONFIG_SMP) && arch_cpu_is_offline(smp_processor_id())) + if (IS_ENABLED(CONFIG_SMP) && arch_cpu_is_offline(smp_processor_id())) { + if (microcode_nmi_handler_enabled()) + microcode_offline_nmi_handler(); return; + }
if (this_cpu_read(nmi_state) != NMI_NOT_RUNNING) { this_cpu_write(nmi_state, NMI_LATCHED);