From: Thomas Gleixner <tglx@linutronix.de>

There is no concurreny.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

---
 arch/x86/kernel/cpu/microcode/intel.c |   24 ++----------------------
 1 file changed, 2 insertions(+), 22 deletions(-)
---
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -397,22 +397,6 @@ scan_microcode(void *data, size_t size,
 	return patch;
 }
 
-/*
- * Save this microcode patch. It will be loaded early when a CPU is
- * hot-added or resumes.
- */
-static void save_mc_for_early(struct ucode_cpu_info *uci, u8 *mc, unsigned int size)
-{
-	/* Synchronization during CPU hotplug. */
-	static DEFINE_MUTEX(x86_cpu_microcode_mutex);
-
-	mutex_lock(&x86_cpu_microcode_mutex);
-
-	save_microcode_patch(uci, mc, size);
-
-	mutex_unlock(&x86_cpu_microcode_mutex);
-}
-
 static bool load_builtin_intel_microcode(struct cpio_data *cp)
 {
 	unsigned int eax = 1, ebx, ecx = 0, edx;
@@ -829,12 +813,8 @@ static enum ucode_state generic_load_mic
 	vfree(uci->mc);
 	uci->mc = (struct microcode_intel *)new_mc;
 
-	/*
-	 * If early loading microcode is supported, save this mc into
-	 * permanent memory. So it will be loaded early when a CPU is hot added
-	 * or resumes.
-	 */
-	save_mc_for_early(uci, new_mc, new_mc_size);
+	/* Save for CPU hotplug */
+	save_microcode_patch(uci, new_mc, new_mc_size);
 
 	pr_debug("CPU%d found a matching microcode update with version 0x%x (current=0x%x)\n",
 		 cpu, new_rev, uci->cpu_sig.rev);

On 12.08.23 г. 22:58 ч., Thomas Gleixner wrote:
> From: Thomas Gleixner <tglx@linutronix.de>
> 
> There is no concurreny.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> 
> ---
>   arch/x86/kernel/cpu/microcode/intel.c |   24 ++----------------------
>   1 file changed, 2 insertions(+), 22 deletions(-)
> ---
> --- a/arch/x86/kernel/cpu/microcode/intel.c
> +++ b/arch/x86/kernel/cpu/microcode/intel.c
> @@ -397,22 +397,6 @@ scan_microcode(void *data, size_t size,
>   	return patch;
>   }
>   
> -/*
> - * Save this microcode patch. It will be loaded early when a CPU is
> - * hot-added or resumes.
> - */
> -static void save_mc_for_early(struct ucode_cpu_info *uci, u8 *mc, unsigned int size)
> -{
> -	/* Synchronization during CPU hotplug. */
> -	static DEFINE_MUTEX(x86_cpu_microcode_mutex);
> -
> -	mutex_lock(&x86_cpu_microcode_mutex);
> -
> -	save_microcode_patch(uci, mc, size);
> -
> -	mutex_unlock(&x86_cpu_microcode_mutex);
> -}
> -


So this function is ultimately invoked from a write to the 'reload' 
sysfs file, what about 2 racing writes to this file ? Though if it's 
about cpu hotplug then in reload_store() this is handled via 
cpus_read_lock I guess so indeed this is correct.

On Sun, Aug 13 2023 at 09:55, Nikolay Borisov wrote:
> On 12.08.23 г. 22:58 ч., Thomas Gleixner wrote:
>
> So this function is ultimately invoked from a write to the 'reload' 
> sysfs file, what about 2 racing writes to this file ? Though if it's 
> about cpu hotplug then in reload_store() this is handled via 
> cpus_read_lock I guess so indeed this is correct.

80347cd515ca ("x86/microcode: Remove microcode_mutex")

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

Commit-ID:     d2700f406713d04573803b9fe8a0fb02c015df39
Gitweb:        https://git.kernel.org/tip/d2700f406713d04573803b9fe8a0fb02c015df39
Author:        Thomas Gleixner <tglx@linutronix.de>
AuthorDate:    Sat, 12 Aug 2023 21:58:50 +02:00
Committer:     Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Sun, 13 Aug 2023 18:42:55 +02:00

x86/microcode/intel: Remove pointless mutex

There is no concurrency.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230812195728.069849788@linutronix.de
---
 arch/x86/kernel/cpu/microcode/intel.c | 24 ++----------------------
 1 file changed, 2 insertions(+), 22 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
index 8621ef4..94dd6af 100644
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -397,22 +397,6 @@ next:
 	return patch;
 }
 
-/*
- * Save this microcode patch. It will be loaded early when a CPU is
- * hot-added or resumes.
- */
-static void save_mc_for_early(struct ucode_cpu_info *uci, u8 *mc, unsigned int size)
-{
-	/* Synchronization during CPU hotplug. */
-	static DEFINE_MUTEX(x86_cpu_microcode_mutex);
-
-	mutex_lock(&x86_cpu_microcode_mutex);
-
-	save_microcode_patch(uci, mc, size);
-
-	mutex_unlock(&x86_cpu_microcode_mutex);
-}
-
 static bool load_builtin_intel_microcode(struct cpio_data *cp)
 {
 	unsigned int eax = 1, ebx, ecx = 0, edx;
@@ -829,12 +813,8 @@ static enum ucode_state generic_load_microcode(int cpu, struct iov_iter *iter)
 	vfree(uci->mc);
 	uci->mc = (struct microcode_intel *)new_mc;
 
-	/*
-	 * If early loading microcode is supported, save this mc into
-	 * permanent memory. So it will be loaded early when a CPU is hot added
-	 * or resumes.
-	 */
-	save_mc_for_early(uci, new_mc, new_mc_size);
+	/* Save for CPU hotplug */
+	save_microcode_patch(uci, new_mc, new_mc_size);
 
 	pr_debug("CPU%d found a matching microcode update with version 0x%x (current=0x%x)\n",
 		 cpu, new_rev, uci->cpu_sig.rev);