From: Borislav Petkov bp@suse.de
[ Upstream commit a77a94f86273ce42a39cb479217dd8d68acfe0ff ]
It is dangerous and it should not be used anyway - there's a nice early loading already.
Requested-by: Peter Zijlstra (Intel) peterz@infradead.org Signed-off-by: Borislav Petkov bp@suse.de Signed-off-by: Thomas Gleixner tglx@linutronix.de Link: https://lore.kernel.org/r/20220525161232.14924-3-bp@alien8.de Stable-dep-of: c0dd9245aa9e ("x86/microcode: Check CPU capabilities after late microcode update correctly") Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/Kconfig | 11 +++++++++++ arch/x86/kernel/cpu/common.c | 2 ++ arch/x86/kernel/cpu/microcode/core.c | 7 ++++++- 3 files changed, 19 insertions(+), 1 deletion(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index da87b3bfc9132..a08ce6360382a 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -1320,6 +1320,17 @@ config MICROCODE_AMD If you select this option, microcode patch loading support for AMD processors will be enabled.
+config MICROCODE_LATE_LOADING + bool "Late microcode loading (DANGEROUS)" + default n + depends on MICROCODE + help + Loading microcode late, when the system is up and executing instructions + is a tricky business and should be avoided if possible. Just the sequence + of synchronizing all cores and SMT threads is one fragile dance which does + not guarantee that cores might not softlock after the loading. Therefore, + use this at your own risk. Late loading taints the kernel too. + config X86_MSR tristate "/dev/cpu/*/msr - Model-specific register support" help diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 1698470dbea5f..6b71f40cd52d6 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -2149,6 +2149,7 @@ void cpu_init_secondary(void) } #endif
+#ifdef CONFIG_MICROCODE_LATE_LOADING /* * The microcode loader calls this upon late microcode load to recheck features, * only when microcode has been updated. Caller holds microcode_mutex and CPU @@ -2178,6 +2179,7 @@ void microcode_check(void) pr_warn("x86/CPU: CPU features have changed after loading microcode, but might not take effect.\n"); pr_warn("x86/CPU: Please consider either early loading through initrd/built-in or a potential BIOS update.\n"); } +#endif
/* * Invoked from core CPU hotplug code after hotplug operations diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c index 951677121c77d..dc346bbb06777 100644 --- a/arch/x86/kernel/cpu/microcode/core.c +++ b/arch/x86/kernel/cpu/microcode/core.c @@ -393,6 +393,7 @@ static int apply_microcode_on_target(int cpu) /* fake device for request_firmware */ static struct platform_device *microcode_pdev;
+#ifdef CONFIG_MICROCODE_LATE_LOADING /* * Late loading dance. Why the heavy-handed stomp_machine effort? * @@ -560,6 +561,9 @@ static ssize_t reload_store(struct device *dev, return ret; }
+static DEVICE_ATTR_WO(reload); +#endif + static ssize_t version_show(struct device *dev, struct device_attribute *attr, char *buf) { @@ -576,7 +580,6 @@ static ssize_t pf_show(struct device *dev, return sprintf(buf, "0x%x\n", uci->cpu_sig.pf); }
-static DEVICE_ATTR_WO(reload); static DEVICE_ATTR(version, 0444, version_show, NULL); static DEVICE_ATTR(processor_flags, 0444, pf_show, NULL);
@@ -729,7 +732,9 @@ static int mc_cpu_down_prep(unsigned int cpu) }
static struct attribute *cpu_root_microcode_attrs[] = { +#ifdef CONFIG_MICROCODE_LATE_LOADING &dev_attr_reload.attr, +#endif NULL };