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x86/microcode: Default-disable late loading 

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
This commit is contained in:
Borislav Petkov 2022-05-25 18:12:30 +02:00 committed by Thomas Gleixner
parent 181b6f40e9
commit a77a94f862
3 changed files with 19 additions and 1 deletions
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11
arch/x86/Kconfig
View File

@ -1350,6 +1350,17 @@ 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

2
arch/x86/kernel/cpu/common.c
View File

@ -2222,6 +2222,7 @@ 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
@ -2251,6 +2252,7 @@ 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

7
arch/x86/kernel/cpu/microcode/core.c
View File

@ -376,6 +376,7 @@ 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?
*
@ -543,6 +544,9 @@ put:
return ret;
}
static DEVICE_ATTR_WO(reload);
#endif
static ssize_t version_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
@ -559,7 +563,6 @@ 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);
@ -712,7 +715,9 @@ 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
};