[PATCH v3] x86/microcode/intel: Reject problematic loading on Granite Rapids systems

["Chang S. Bae" <chang.seok.bae@intel.com>]

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

Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: <stable@vger.kernel.org>
---
V2 -> V3:
* Shorten the changelog and rename the function (Boris)
* Reduce the code comment (Dave)
* Allow 0x1000405 loading. Thanks to Andrew, this fix got attention.
* Collect Dave review tag. Thanks, Dave!

Note:
* GNR98 currently describes loading 0x1000405 itself is unsafe, but it
  will be updated to say okay with that. I will watch out the GNR98
  changes.
* Jumping from < 0x1000380 to 0x1000405 was identified as an issue, but
  0x1000380 is the first revision as GNR products. So loading 0x1000405
  in production systems should be okay.
---
 arch/x86/kernel/cpu/microcode/intel.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
index 1142183c950c..30a22388d4b1 100644
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -309,6 +309,26 @@ static void save_microcode_patch(struct microcode_intel *patch)
 		pr_err("Unable to allocate microcode memory size: %u\n", size);
 }
 
+static bool revision_is_safe(struct cpu_signature *sig, u32 rev)
+{
+	u32 vfm = IFM(x86_family(sig->sig), x86_model(sig->sig));
+
+	/*
+	 * Erratum GNR98 can cause #MC's if "jumping over" revision 0x1000405.
+	 * Avoid the jumps.
+	 */
+	if (vfm == INTEL_GRANITERAPIDS_X &&
+	    x86_stepping(sig->sig) == 1 &&
+	    sig->pf & 0x95 &&
+	    sig->rev < 0x1000405 &&
+	    rev > 0x1000405) {
+		pr_err_once("Erratum GNR98: skipping revision 0x%x.\n", rev);
+		return false;
+	}
+
+	return true;
+}
+
 /* 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 +350,9 @@ static __init struct microcode_intel *scan_microcode(void *data, size_t size,
 		if (!intel_find_matching_signature(data, &uci->cpu_sig))
 			continue;
 
+		if (!revision_is_safe(&uci->cpu_sig, mc_header->rev))
+			continue;
+
 		/*
 		 * For saving the early microcode, find the matching revision which
 		 * was loaded on the BSP.
@@ -878,6 +901,9 @@ 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_is_safe(&uci->cpu_sig, mc_header.rev))
+			continue;
+
 		is_safe = ucode_validate_minrev(&mc_header);
 		if (force_minrev && !is_safe)
 			continue;
-- 
2.53.0