[PATCH 0/4] x86/microcode: Drop old interface and default-disable late loading

[PATCH 0/4] x86/microcode: Drop old interface and default-disable late loading

[Borislav Petkov]

From: Borislav Petkov <bp@suse.de>

Now tested.

AMD:

[  349.234368] microcode: Attempting late microcode loading - it is dangerous and taints the kernel.
[  349.244128] microcode: You should switch to early loading, if possible.
...
[  349.391934] microcode: Reload completed, microcode revision: 0xa001173

Intel:

[   50.726917] microcode: Attempting late microcode loading - it is dangerous and taints the kernel.
[   50.736139] microcode: You should switch to early loading, if possible.
[   50.745504] microcode: updated to revision 0x718, date = 2019-05-21
[   50.752000] x86/CPU: CPU features have changed after loading microcode, but might not take effect.
[   50.761158] x86/CPU: Please consider either early loading through initrd/built-in or a potential BIOS update.
[   50.771362] microcode: Reload completed, microcode revision: 0x718

Changelog:
----------

v0:

Totally untested, just sending out as a RFC first. This is something
Peter and I talked about recently and think it makes sense.

Borislav Petkov (4):
  x86/microcode: Rip out the OLD_INTERFACE
  x86/microcode: Default-disable late loading
  x86/microcode: Taint and warn on late loading
  x86/microcode: Remove unnecessary perf callback

 arch/x86/Kconfig                     |  15 ++--
 arch/x86/kernel/cpu/common.c         |   2 +
 arch/x86/kernel/cpu/microcode/core.c | 115 +++------------------------
 3 files changed, 20 insertions(+), 112 deletions(-)

-- 
2.35.1

[PATCH 1/4] x86/microcode: Rip out the OLD_INTERFACE

[Borislav Petkov]

From: Borislav Petkov <bp@suse.de>

Everything should be using the early initrd loading by now.

Signed-off-by: Borislav Petkov <bp@suse.de>
---
 arch/x86/Kconfig                     |  12 ----
 arch/x86/kernel/cpu/microcode/core.c | 100 ---------------------------
 2 files changed, 112 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 2e8f6fd28e59..1c0da2dbfb26 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1345,18 +1345,6 @@ config MICROCODE_AMD
 	  If you select this option, microcode patch loading support for AMD
 	  processors will be enabled.
 
-config MICROCODE_OLD_INTERFACE
-	bool "Ancient loading interface (DEPRECATED)"
-	default n
-	depends on MICROCODE
-	help
-	  DO NOT USE THIS! This is the ancient /dev/cpu/microcode interface
-	  which was used by userspace tools like iucode_tool and microcode.ctl.
-	  It is inadequate because it runs too late to be able to properly
-	  load microcode on a machine and it needs special tools. Instead, you
-	  should've switched to the early loading method with the initrd or
-	  builtin microcode by now: Documentation/x86/microcode.rst
-
 config X86_MSR
 	tristate "/dev/cpu/*/msr - Model-specific register support"
 	help
diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index 239ff5fcec6a..b72c4134f289 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -373,98 +373,6 @@ static int apply_microcode_on_target(int cpu)
 	return ret;
 }
 
-#ifdef CONFIG_MICROCODE_OLD_INTERFACE
-static int do_microcode_update(const void __user *buf, size_t size)
-{
-	int error = 0;
-	int cpu;
-
-	for_each_online_cpu(cpu) {
-		struct ucode_cpu_info *uci = ucode_cpu_info + cpu;
-		enum ucode_state ustate;
-
-		if (!uci->valid)
-			continue;
-
-		ustate = microcode_ops->request_microcode_user(cpu, buf, size);
-		if (ustate == UCODE_ERROR) {
-			error = -1;
-			break;
-		} else if (ustate == UCODE_NEW) {
-			apply_microcode_on_target(cpu);
-		}
-	}
-
-	return error;
-}
-
-static int microcode_open(struct inode *inode, struct file *file)
-{
-	return capable(CAP_SYS_RAWIO) ? stream_open(inode, file) : -EPERM;
-}
-
-static ssize_t microcode_write(struct file *file, const char __user *buf,
-			       size_t len, loff_t *ppos)
-{
-	ssize_t ret = -EINVAL;
-	unsigned long nr_pages = totalram_pages();
-
-	if ((len >> PAGE_SHIFT) > nr_pages) {
-		pr_err("too much data (max %ld pages)\n", nr_pages);
-		return ret;
-	}
-
-	cpus_read_lock();
-	mutex_lock(&microcode_mutex);
-
-	if (do_microcode_update(buf, len) == 0)
-		ret = (ssize_t)len;
-
-	if (ret > 0)
-		perf_check_microcode();
-
-	mutex_unlock(&microcode_mutex);
-	cpus_read_unlock();
-
-	return ret;
-}
-
-static const struct file_operations microcode_fops = {
-	.owner			= THIS_MODULE,
-	.write			= microcode_write,
-	.open			= microcode_open,
-	.llseek		= no_llseek,
-};
-
-static struct miscdevice microcode_dev = {
-	.minor			= MICROCODE_MINOR,
-	.name			= "microcode",
-	.nodename		= "cpu/microcode",
-	.fops			= &microcode_fops,
-};
-
-static int __init microcode_dev_init(void)
-{
-	int error;
-
-	error = misc_register(&microcode_dev);
-	if (error) {
-		pr_err("can't misc_register on minor=%d\n", MICROCODE_MINOR);
-		return error;
-	}
-
-	return 0;
-}
-
-static void __exit microcode_dev_exit(void)
-{
-	misc_deregister(&microcode_dev);
-}
-#else
-#define microcode_dev_init()	0
-#define microcode_dev_exit()	do { } while (0)
-#endif
-
 /* fake device for request_firmware */
 static struct platform_device	*microcode_pdev;
 
@@ -856,10 +764,6 @@ static int __init microcode_init(void)
 		goto out_driver;
 	}
 
-	error = microcode_dev_init();
-	if (error)
-		goto out_ucode_group;
-
 	register_syscore_ops(&mc_syscore_ops);
 	cpuhp_setup_state_nocalls(CPUHP_AP_MICROCODE_LOADER, "x86/microcode:starting",
 				  mc_cpu_starting, NULL);
@@ -870,10 +774,6 @@ static int __init microcode_init(void)
 
 	return 0;
 
- out_ucode_group:
-	sysfs_remove_group(&cpu_subsys.dev_root->kobj,
-			   &cpu_root_microcode_group);
-
  out_driver:
 	cpus_read_lock();
 	mutex_lock(&microcode_mutex);
-- 
2.35.1

[PATCH 2/4] x86/microcode: Default-disable late loading

[Borislav Petkov]

From: Borislav Petkov <bp@suse.de>

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>
---
 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 1c0da2dbfb26..33891b82fb65 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1345,6 +1345,17 @@ 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 2e9142797c99..c296cb1c0113 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -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
diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index b72c4134f289..c717db6b6856 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -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 @@ 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)
 {
@@ -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
 };
 
-- 
2.35.1

[PATCH 3/4] x86/microcode: Taint and warn on late loading

[Borislav Petkov]

From: Borislav Petkov <bp@suse.de>

Warn before it is attempted and taint the kernel.

Signed-off-by: Borislav Petkov <bp@suse.de>
---
 arch/x86/kernel/cpu/microcode/core.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index c717db6b6856..801b44ac3851 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -493,6 +493,9 @@ static int microcode_reload_late(void)
 {
 	int ret;
 
+	pr_err("Attempting late microcode loading - it is dangerous and taints the kernel.\n");
+	pr_err("You should switch to early loading, if possible.\n");
+
 	atomic_set(&late_cpus_in,  0);
 	atomic_set(&late_cpus_out, 0);
 
@@ -541,6 +544,8 @@ static ssize_t reload_store(struct device *dev,
 	if (ret == 0)
 		ret = size;
 
+	add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
+
 	return ret;
 }
 
-- 
2.35.1

[PATCH 4/4] x86/microcode: Remove unnecessary perf callback

[Borislav Petkov]

From: Borislav Petkov <bp@suse.de>

c93dc84cbe32 ("perf/x86: Add a microcode revision check for SNB-PEBS")
checks whether the microcode revision has fixed PEBS issues.

This can happen either:

1. At PEBS init time, where the early microcode has been loaded already

2. During late loading, in the microcode_check() callback.

So remove the unnecessary call in the microcode loader init routine.

Signed-off-by: Borislav Petkov <bp@suse.de>
---
 arch/x86/kernel/cpu/microcode/core.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index 801b44ac3851..ad57e0e4d674 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -756,10 +756,7 @@ static int __init microcode_init(void)
 
 	cpus_read_lock();
 	mutex_lock(&microcode_mutex);
-
 	error = subsys_interface_register(&mc_cpu_interface);
-	if (!error)
-		perf_check_microcode();
 	mutex_unlock(&microcode_mutex);
 	cpus_read_unlock();
 
-- 
2.35.1

[tip: x86/microcode] x86/microcode: Remove unnecessary perf callback

[tip-bot2 for Borislav Petkov]

The following commit has been merged into the x86/microcode branch of tip:

Commit-ID:     0c0fe08c76485fe0178ebb0fa1a2052c727abe94
Gitweb:        https://git.kernel.org/tip/0c0fe08c76485fe0178ebb0fa1a2052c727abe94
Author:        Borislav Petkov <bp@suse.de>
AuthorDate:    Wed, 25 May 2022 18:12:32 +02:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Tue, 31 May 2022 09:31:19 +02:00

x86/microcode: Remove unnecessary perf callback

c93dc84cbe32 ("perf/x86: Add a microcode revision check for SNB-PEBS")
checks whether the microcode revision has fixed PEBS issues.

This can happen either:

1. At PEBS init time, where the early microcode has been loaded already

2. During late loading, in the microcode_check() callback.

So remove the unnecessary call in the microcode loader init routine.

Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20220525161232.14924-5-bp@alien8.de

---
 arch/x86/kernel/cpu/microcode/core.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index 801b44a..ad57e0e 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -756,10 +756,7 @@ static int __init microcode_init(void)
 
 	cpus_read_lock();
 	mutex_lock(&microcode_mutex);
-
 	error = subsys_interface_register(&mc_cpu_interface);
-	if (!error)
-		perf_check_microcode();
 	mutex_unlock(&microcode_mutex);
 	cpus_read_unlock();
 

[tip: x86/microcode] x86/microcode: Taint and warn on late loading

[tip-bot2 for Borislav Petkov]

The following commit has been merged into the x86/microcode branch of tip:

Commit-ID:     d23d33ea0fcdc4bbb484990bf53867f99c63ccab
Gitweb:        https://git.kernel.org/tip/d23d33ea0fcdc4bbb484990bf53867f99c63ccab
Author:        Borislav Petkov <bp@suse.de>
AuthorDate:    Wed, 25 May 2022 18:12:31 +02:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Tue, 31 May 2022 09:31:19 +02:00

x86/microcode: Taint and warn on late loading

Warn before it is attempted and taint the kernel. Late loading microcode
can lead to malfunction of the kernel when the microcode update changes
behaviour. There is no way for the kernel to determine whether its safe or
not.

Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20220525161232.14924-4-bp@alien8.de

---
 arch/x86/kernel/cpu/microcode/core.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index c717db6..801b44a 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -493,6 +493,9 @@ static int microcode_reload_late(void)
 {
 	int ret;
 
+	pr_err("Attempting late microcode loading - it is dangerous and taints the kernel.\n");
+	pr_err("You should switch to early loading, if possible.\n");
+
 	atomic_set(&late_cpus_in,  0);
 	atomic_set(&late_cpus_out, 0);
 
@@ -541,6 +544,8 @@ put:
 	if (ret == 0)
 		ret = size;
 
+	add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
+
 	return ret;
 }
 

[tip: x86/microcode] x86/microcode: Default-disable late loading

[tip-bot2 for Borislav Petkov]

The following commit has been merged into the x86/microcode branch of tip:

Commit-ID:     a77a94f86273ce42a39cb479217dd8d68acfe0ff
Gitweb:        https://git.kernel.org/tip/a77a94f86273ce42a39cb479217dd8d68acfe0ff
Author:        Borislav Petkov <bp@suse.de>
AuthorDate:    Wed, 25 May 2022 18:12:30 +02:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Tue, 31 May 2022 09:31:19 +02:00

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
---
 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 f423a2d..976309d 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -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
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 2e91427..c296cb1 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -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
diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index b72c413..c717db6 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -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
 };
 

[tip: x86/microcode] x86/microcode: Rip out the OLD_INTERFACE

[tip-bot2 for Borislav Petkov]

The following commit has been merged into the x86/microcode branch of tip:

Commit-ID:     181b6f40e9ea80c76756d4d0cdeed396016c487e
Gitweb:        https://git.kernel.org/tip/181b6f40e9ea80c76756d4d0cdeed396016c487e
Author:        Borislav Petkov <bp@suse.de>
AuthorDate:    Wed, 25 May 2022 18:12:29 +02:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Tue, 31 May 2022 09:31:19 +02:00

x86/microcode: Rip out the OLD_INTERFACE

Everything should be using the early initrd loading by now.

Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20220525161232.14924-2-bp@alien8.de

---
 arch/x86/Kconfig                     |  12 +---
 arch/x86/kernel/cpu/microcode/core.c | 100 +--------------------------
 2 files changed, 112 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 762a0b6..f423a2d 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1350,18 +1350,6 @@ config MICROCODE_AMD
 	  If you select this option, microcode patch loading support for AMD
 	  processors will be enabled.
 
-config MICROCODE_OLD_INTERFACE
-	bool "Ancient loading interface (DEPRECATED)"
-	default n
-	depends on MICROCODE
-	help
-	  DO NOT USE THIS! This is the ancient /dev/cpu/microcode interface
-	  which was used by userspace tools like iucode_tool and microcode.ctl.
-	  It is inadequate because it runs too late to be able to properly
-	  load microcode on a machine and it needs special tools. Instead, you
-	  should've switched to the early loading method with the initrd or
-	  builtin microcode by now: Documentation/x86/microcode.rst
-
 config X86_MSR
 	tristate "/dev/cpu/*/msr - Model-specific register support"
 	help
diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index 239ff5f..b72c413 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -373,98 +373,6 @@ static int apply_microcode_on_target(int cpu)
 	return ret;
 }
 
-#ifdef CONFIG_MICROCODE_OLD_INTERFACE
-static int do_microcode_update(const void __user *buf, size_t size)
-{
-	int error = 0;
-	int cpu;
-
-	for_each_online_cpu(cpu) {
-		struct ucode_cpu_info *uci = ucode_cpu_info + cpu;
-		enum ucode_state ustate;
-
-		if (!uci->valid)
-			continue;
-
-		ustate = microcode_ops->request_microcode_user(cpu, buf, size);
-		if (ustate == UCODE_ERROR) {
-			error = -1;
-			break;
-		} else if (ustate == UCODE_NEW) {
-			apply_microcode_on_target(cpu);
-		}
-	}
-
-	return error;
-}
-
-static int microcode_open(struct inode *inode, struct file *file)
-{
-	return capable(CAP_SYS_RAWIO) ? stream_open(inode, file) : -EPERM;
-}
-
-static ssize_t microcode_write(struct file *file, const char __user *buf,
-			       size_t len, loff_t *ppos)
-{
-	ssize_t ret = -EINVAL;
-	unsigned long nr_pages = totalram_pages();
-
-	if ((len >> PAGE_SHIFT) > nr_pages) {
-		pr_err("too much data (max %ld pages)\n", nr_pages);
-		return ret;
-	}
-
-	cpus_read_lock();
-	mutex_lock(&microcode_mutex);
-
-	if (do_microcode_update(buf, len) == 0)
-		ret = (ssize_t)len;
-
-	if (ret > 0)
-		perf_check_microcode();
-
-	mutex_unlock(&microcode_mutex);
-	cpus_read_unlock();
-
-	return ret;
-}
-
-static const struct file_operations microcode_fops = {
-	.owner			= THIS_MODULE,
-	.write			= microcode_write,
-	.open			= microcode_open,
-	.llseek		= no_llseek,
-};
-
-static struct miscdevice microcode_dev = {
-	.minor			= MICROCODE_MINOR,
-	.name			= "microcode",
-	.nodename		= "cpu/microcode",
-	.fops			= &microcode_fops,
-};
-
-static int __init microcode_dev_init(void)
-{
-	int error;
-
-	error = misc_register(&microcode_dev);
-	if (error) {
-		pr_err("can't misc_register on minor=%d\n", MICROCODE_MINOR);
-		return error;
-	}
-
-	return 0;
-}
-
-static void __exit microcode_dev_exit(void)
-{
-	misc_deregister(&microcode_dev);
-}
-#else
-#define microcode_dev_init()	0
-#define microcode_dev_exit()	do { } while (0)
-#endif
-
 /* fake device for request_firmware */
 static struct platform_device	*microcode_pdev;
 
@@ -856,10 +764,6 @@ static int __init microcode_init(void)
 		goto out_driver;
 	}
 
-	error = microcode_dev_init();
-	if (error)
-		goto out_ucode_group;
-
 	register_syscore_ops(&mc_syscore_ops);
 	cpuhp_setup_state_nocalls(CPUHP_AP_MICROCODE_LOADER, "x86/microcode:starting",
 				  mc_cpu_starting, NULL);
@@ -870,10 +774,6 @@ static int __init microcode_init(void)
 
 	return 0;
 
- out_ucode_group:
-	sysfs_remove_group(&cpu_subsys.dev_root->kobj,
-			   &cpu_root_microcode_group);
-
  out_driver:
 	cpus_read_lock();
 	mutex_lock(&microcode_mutex);