[PATCH v2] x86/microcode/intel: Reject problematic loading on Granite Rapids systems

[Chang S. Bae]

Microcode updates can usually jump revisions. However, there is an
erratum on Granite Rapids systems. If they "jump over" to revision
0x1000405 or later, they result in #MC.

Prevent loading 0x1000405 or later unless the running revision is already
at least 0x1000405. Apply this blocking to both early- and late-loading
paths.

Signed-off-by: Chang S. Bae <chang.seok.bae@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
---
V1 -> V2:
* Cut the code comments and print messages (Boris)
* Rename the new function and keep the old function as it-is (Boris)
* Rewrote the changelog (Dave)
* Add `revision` in the error messages (Sohil)
---
 arch/x86/kernel/cpu/microcode/intel.c | 32 +++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
index 1142183c950c..61ad280497e9 100644
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -309,6 +309,32 @@ static void save_microcode_patch(struct microcode_intel *patch)
 		pr_err("Unable to allocate microcode memory size: %u\n", size);
 }
 
+static bool revision_banned(struct cpu_signature *sig, u32 rev)
+{
+	u32 vfm = IFM(x86_family(sig->sig), x86_model(sig->sig));
+
+	/*
+	 * Revision 0x1000405 contains prerequisite changes for subsequent
+	 * microcode updates on Granite Rapids systems. Updates directly from
+	 * an older revision to this or a newer one can result in #MC. This is
+	 * documented item GNR98, #835486 (Intel Xeon 6900/6700/6500-Series
+	 * Processors with P-Cores).
+	 */
+	if (vfm == INTEL_GRANITERAPIDS_X &&
+	    x86_stepping(sig->sig) == 1 &&
+	    sig->pf & 0x95 &&
+	    sig->rev < 0x1000405 &&
+	    rev >= 0x1000405) {
+		if (rev == 0x1000405)
+			pr_err_once("Erratum GNR98: revision 0x1000405 is not loadable.\n");
+		else
+			pr_err_once("Erratum GNR98: revision 0x1000405 is required before 0x%x.\n", rev);
+		return true;
+	}
+
+	return false;
+}
+
 /* Scan blob for microcode matching the boot CPUs family, model, stepping */
 static __init struct microcode_intel *scan_microcode(void *data, size_t size,
 						     struct ucode_cpu_info *uci,
@@ -330,6 +356,9 @@ static __init struct microcode_intel *scan_microcode(void *data, size_t size,
 		if (!intel_find_matching_signature(data, &uci->cpu_sig))
 			continue;
 
+		if (revision_banned(&uci->cpu_sig, mc_header->rev))
+			continue;
+
 		/*
 		 * For saving the early microcode, find the matching revision which
 		 * was loaded on the BSP.
@@ -878,6 +907,9 @@ static enum ucode_state parse_microcode_blobs(int cpu, struct iov_iter *iter)
 		if (!intel_find_matching_signature(mc, &uci->cpu_sig))
 			continue;
 
+		if (revision_banned(&uci->cpu_sig, mc_header.rev))
+			continue;
+
 		is_safe = ucode_validate_minrev(&mc_header);
 		if (force_minrev && !is_safe)
 			continue;
-- 
2.53.0