linux-kernel - [PATCH v6 3/7] x86/microcode/intel: Establish staging control logic

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Message-ID: <20250921224841.3545-4-chang.seok.bae@intel.com>
Date: Sun, 21 Sep 2025 15:48:37 -0700
From: "Chang S. Bae" <chang.seok.bae@...el.com>
To: linux-kernel@...r.kernel.org
Cc: x86@...nel.org,
	tglx@...utronix.de,
	mingo@...hat.com,
	bp@...en8.de,
	dave.hansen@...ux.intel.com,
	chao.gao@...el.com,
	abusse@...zon.de,
	tony.luck@...el.com,
	chang.seok.bae@...el.com
Subject: [PATCH v6 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@...utronix.de>
Signed-off-by: Chang S. Bae <chang.seok.bae@...el.com>
Tested-by: Anselm Busse <abusse@...zon.de>
Reviewed-by: Tony Luck <tony.luck@...el.com>
Link: https://lore.kernel.org/all/871pznq229.ffs@tglx
---
V5 -> V6:
* Remove stale text in changelog (Boris)
* Place MSR definition in the right spot in msr-index.h (Boris)
* Dump error code instead of vague message (Boris)
* Collect Tony's review tag

V4 -> V5:
* Rebase on the primary thread cpumask fix (Dave)
* Clean up the revision print code (Dave)
* rdmsrl_on_cpu() -> rdmsrq_on_cpu (Chao)

V2 -> V3:
* Remove a global variable and adjust stage_microcode() (Dave).
* Simplify for_each_cpu() loop control code
* Handle rdmsrl_on_cpu() return code explicitly (Chao)

V1 -> V2:
* Adjust to reference the staging_state struct.
* Add lockdep_assert_cpus_held() (Boris)
---
 arch/x86/include/asm/msr-index.h      |  2 ++
 arch/x86/kernel/cpu/microcode/intel.c | 48 +++++++++++++++++++++++++++
 2 files changed, 50 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..daae74858347 100644
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -299,6 +299,53 @@ 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)))
+		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 (code = %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 +674,7 @@ 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