From 93946a33b5693a6bbcf917a170198ff4afaa7a31 Mon Sep 17 00:00:00 2001 From: Ashok Raj Date: Thu, 22 Aug 2019 23:43:47 +0300 Subject: [PATCH] x86/microcode: Update late microcode in parallel Microcode update was changed to be serialized due to restrictions after Spectre days. Updating serially on a large multi-socket system can be painful since it is being done on one CPU at a time. Cloud customers have expressed discontent as services disappear for a prolonged time. The restriction is that only one core (or only one thread of a core in the case of an SMT system) goes through the update while other cores (or respectively, SMT threads) are quiesced. Do the microcode update only on the first thread of each core while other siblings simply wait for this to complete. [ bp: Simplify, massage, cleanup comments. ] Signed-off-by: Ashok Raj Signed-off-by: Mihai Carabas Signed-off-by: Borislav Petkov Cc: Boris Ostrovsky Cc: "H. Peter Anvin" Cc: Ingo Molnar Cc: Jon Grimm Cc: kanth.ghatraju@oracle.com Cc: konrad.wilk@oracle.com Cc: patrick.colp@oracle.com Cc: Thomas Gleixner Cc: Tom Lendacky Cc: x86-ml Link: https://lkml.kernel.org/r/1566506627-16536-2-git-send-email-mihai.carabas@oracle.com --- arch/x86/kernel/cpu/microcode/core.c | 36 ++++++++++++++++------------ 1 file changed, 21 insertions(+), 15 deletions(-) diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c index cb0fdcaf1415..7019d4b2df0c 100644 --- a/arch/x86/kernel/cpu/microcode/core.c +++ b/arch/x86/kernel/cpu/microcode/core.c @@ -63,11 +63,6 @@ LIST_HEAD(microcode_cache); */ static DEFINE_MUTEX(microcode_mutex); -/* - * Serialize late loading so that CPUs get updated one-by-one. - */ -static DEFINE_RAW_SPINLOCK(update_lock); - struct ucode_cpu_info ucode_cpu_info[NR_CPUS]; struct cpu_info_ctx { @@ -566,11 +561,18 @@ static int __reload_late(void *info) if (__wait_for_cpus(&late_cpus_in, NSEC_PER_SEC)) return -1; - raw_spin_lock(&update_lock); - apply_microcode_local(&err); - raw_spin_unlock(&update_lock); + /* + * On an SMT system, it suffices to load the microcode on one sibling of + * the core because the microcode engine is shared between the threads. + * Synchronization still needs to take place so that no concurrent + * loading attempts happen on multiple threads of an SMT core. See + * below. + */ + if (cpumask_first(topology_sibling_cpumask(cpu)) == cpu) + apply_microcode_local(&err); + else + goto wait_for_siblings; - /* siblings return UCODE_OK because their engine got updated already */ if (err > UCODE_NFOUND) { pr_warn("Error reloading microcode on CPU %d\n", cpu); ret = -1; @@ -578,14 +580,18 @@ static int __reload_late(void *info) ret = 1; } +wait_for_siblings: + if (__wait_for_cpus(&late_cpus_out, NSEC_PER_SEC)) + panic("Timeout during microcode update!\n"); + /* - * Increase the wait timeout to a safe value here since we're - * serializing the microcode update and that could take a while on a - * large number of CPUs. And that is fine as the *actual* timeout will - * be determined by the last CPU finished updating and thus cut short. + * At least one thread has completed update on each core. + * For others, simply call the update to make sure the + * per-cpu cpuinfo can be updated with right microcode + * revision. */ - if (__wait_for_cpus(&late_cpus_out, NSEC_PER_SEC * num_online_cpus())) - panic("Timeout during microcode update!\n"); + if (cpumask_first(topology_sibling_cpumask(cpu)) != cpu) + apply_microcode_local(&err); return ret; } -- 2.45.2