Re: [PATCH v6 3/7] x86/microcode/intel: Establish staging control logic

[Chang S. Bae]

On 10/13/2025 6:42 AM, Borislav Petkov wrote:
> Fixups ontop:

Thanks!

> diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
> index daae74858347..216595a45564 100644
> --- a/arch/x86/kernel/cpu/microcode/intel.c
> +++ b/arch/x86/kernel/cpu/microcode/intel.c
> @@ -315,15 +315,18 @@ static void stage_microcode(void)
>   	int cpu, err;
>   	u64 mmio_pa;
>   
> -	if (!IS_ALIGNED(get_totalsize(&ucode_patch_late->hdr), sizeof(u32)))
> +	if (!IS_ALIGNED(get_totalsize(&ucode_patch_late->hdr), sizeof(u32))) {
> +		pr_err("Microcode image 32-bit misaligned (0x%x), staging failed.\n",
> +			get_totalsize(&ucode_patch_late->hdr));
>   		return;
> +	}

Yeah, need to keep in mind more consistent about emitting error messages 
in this area.

Include the updated patch:

From 809f1845cf76023f97b8f9c03dd8e10fdda2aac6 Mon Sep 17 00:00:00 2001
From: "Chang S. Bae" <chang.seok.bae@xxxxxxxxx>
Date: Fri, 15 Mar 2024 23:05:34 -0700
Subject: [PATCH v6a 3/7] x86/microcode/intel: Establish staging control logic

When microcode staging is initiated, operations are carried out through
an MMIO interface. Each package has a unique interface specified by the
IA32_MCU_STAGING_MBOX_ADDR MSR, which maps to a set of 32-bit registers.

Prepare staging with the following steps:

  1.  Ensure the microcode image is 32-bit aligned to match the MMIO
      register size.

  2.  Identify each MMIO interface based on its per-package scope.

  3.  Invoke the staging function for each identified interface, which
      will be implemented separately.

Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Chang S. Bae <chang.seok.bae@xxxxxxxxx>
Tested-by: Anselm Busse <abusse@xxxxxxxxx>
Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
Link: https://lore.kernel.org/all/871pznq229.ffs@tglx
---
V6 -> V6a:
* Add an error message for misaligned image size (Boris)
* Fix typo: id -> ID (Boris)
* Shorten the error code printout (Boris)
---
 arch/x86/include/asm/msr-index.h      |  2 ++
 arch/x86/kernel/cpu/microcode/intel.c | 51 +++++++++++++++++++++++++++
 2 files changed, 53 insertions(+)

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 718a55d82fe4..0736e44f7c69 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -1222,6 +1222,8 @@
 #define MSR_IA32_VMX_VMFUNC             0x00000491
 #define MSR_IA32_VMX_PROCBASED_CTLS3	0x00000492
 
+#define MSR_IA32_MCU_STAGING_MBOX_ADDR	0x000007a5
+
 /* Resctrl MSRs: */
 /* - Intel: */
 #define MSR_IA32_L3_QOS_CFG		0xc81
diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
index 371ca6eac00e..216595a45564 100644
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -299,6 +299,56 @@ static __init struct microcode_intel *scan_microcode(void *data, size_t size,
 	return size ? NULL : patch;
 }
 
+/*
+ * Handle the staging process using the mailbox MMIO interface.
+ * Return 0 on success or an error code on failure.
+ */
+static int do_stage(u64 mmio_pa)
+{
+	pr_debug_once("Staging implementation is pending.\n");
+	return -EPROTONOSUPPORT;
+}
+
+static void stage_microcode(void)
+{
+	unsigned int pkg_id = UINT_MAX;
+	int cpu, err;
+	u64 mmio_pa;
+
+	if (!IS_ALIGNED(get_totalsize(&ucode_patch_late->hdr), sizeof(u32))) {
+		pr_err("Microcode image 32-bit misaligned (0x%x), staging failed.\n",
+			get_totalsize(&ucode_patch_late->hdr));
+		return;
+	}
+
+	lockdep_assert_cpus_held();
+
+	/*
+	 * The MMIO address is unique per package, and all the SMT
+	 * primary threads are online here. Find each MMIO space by
+	 * their package IDs to avoid duplicate staging.
+	 */
+	for_each_cpu(cpu, cpu_primary_thread_mask) {
+		if (topology_logical_package_id(cpu) == pkg_id)
+			continue;
+
+		pkg_id = topology_logical_package_id(cpu);
+
+		err = rdmsrq_on_cpu(cpu, MSR_IA32_MCU_STAGING_MBOX_ADDR, &mmio_pa);
+		if (WARN_ON_ONCE(err))
+			return;
+
+		err = do_stage(mmio_pa);
+		if (err) {
+			pr_err("Error: staging failed (%d) for CPU%d at package %u.\n",
+			       err, cpu, pkg_id);
+			return;
+		}
+	}
+
+	pr_info("Staging of patch revision 0x%x succeeded.\n", ucode_patch_late->hdr.rev);
+}
+
 static enum ucode_state __apply_microcode(struct ucode_cpu_info *uci,
 					  struct microcode_intel *mc,
 					  u32 *cur_rev)
@@ -627,6 +677,7 @@ static struct microcode_ops microcode_intel_ops = {
 	.collect_cpu_info	= collect_cpu_info,
 	.apply_microcode	= apply_microcode_late,
 	.finalize_late_load	= finalize_late_load,
+	.stage_microcode	= stage_microcode,
 	.use_nmi		= IS_ENABLED(CONFIG_X86_64),
 };
 
-- 
2.48.1