linux-kernel - [PATCH v2a 3/6] x86/microcode/intel: Establish staging control logic

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Message-ID: <20250321211853.13909-1-chang.seok.bae@intel.com>
Date: Fri, 21 Mar 2025 14:18:53 -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,
	colinmitchell@...gle.com,
	chang.seok.bae@...el.com
Subject: [PATCH v2a 3/6] 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>
Link: https://lore.kernel.org/all/871pznq229.ffs@tglx
---
V2 -> V2a:
* Remove a global variable and adjust stage_microcode() (Dave [1]).

Note: this quick revision is just intended to ensure that the feedback
has been properly addressed.

[1]: https://lore.kernel.org/lkml/b01224ee-c935-4b08-a76f-5dc49341182d@intel.com/
---
 arch/x86/include/asm/msr-index.h      |  2 ++
 arch/x86/kernel/cpu/microcode/intel.c | 49 +++++++++++++++++++++++++++
 2 files changed, 51 insertions(+)

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index bc6d2de109b5..f123abfdffcb 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -891,6 +891,8 @@
 #define MSR_IA32_UCODE_WRITE		0x00000079
 #define MSR_IA32_UCODE_REV		0x0000008b
 
+#define MSR_IA32_MCU_STAGING_MBOX_ADDR	0x000007a5
+
 /* Intel SGX Launch Enclave Public Key Hash MSRs */
 #define MSR_IA32_SGXLEPUBKEYHASH0	0x0000008C
 #define MSR_IA32_SGXLEPUBKEYHASH1	0x0000008D
diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
index 57ed5d414cd1..5d0216e9aee5 100644
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -320,6 +320,54 @@ 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 the result state.
+ */
+static enum ucode_state do_stage(u64 mmio_pa)
+{
+	pr_debug_once("Staging implementation is pending.\n");
+	return UCODE_ERROR;
+}
+
+static void stage_microcode(void)
+{
+	unsigned int pkg_id = UINT_MAX;
+	enum ucode_state ret;
+	u64 mmio_pa;
+	int cpu;
+
+	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_online_mask) {
+		if (!topology_is_primary_thread(cpu) ||
+		     topology_logical_package_id(cpu) == pkg_id)
+			continue;
+		pkg_id = topology_logical_package_id(cpu);
+
+		rdmsrl_on_cpu(cpu, MSR_IA32_MCU_STAGING_MBOX_ADDR, &mmio_pa);
+
+		ret = do_stage(mmio_pa);
+		if (ret != UCODE_OK) {
+			pr_err("Error: staging failed with %s for CPU%d at package %u.\n",
+			       ret == UCODE_TIMEOUT ? "timeout" : "error state",
+			       cpu, pkg_id);
+			return;
+		}
+	}
+
+	pr_info("Staging of patch revision 0x%x succeeded.\n",
+		((struct microcode_header_intel *)ucode_patch_late)->rev);
+}
+
 static enum ucode_state __apply_microcode(struct ucode_cpu_info *uci,
 					  struct microcode_intel *mc,
 					  u32 *cur_rev)
@@ -648,6 +696,7 @@ 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),
 };
 
-- 
2.45.2