x86/MCE/AMD: Split amd_mce_is_memory_error()

Define helper functions for legacy and SMCA systems in order to reuse
individual checks in later changes.

Describe what each function is checking for, and correct the XEC bitmask
for SMCA.

No functional change intended.

  [ bp: Use "else in amd_mce_is_memory_error() to make the conditional
    balanced, for readability. ]

Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Shuai Xue <xueshuai@linux.alibaba.com>
Link: https://lore.kernel.org/r/20230613141142.36801-2-yazen.ghannam@amd.com

Author: yghannam

arch/x86/kernel/cpu/mce/amd.c

@@ -713,17 +713,37 @@ void mce_amd_feature_init(struct cpuinfo_x86 *c)
 		deferred_error_interrupt_enable(c);
 }
 
-bool amd_mce_is_memory_error(struct mce *m)
+/*
+ * DRAM ECC errors are reported in the Northbridge (bank 4) with
+ * Extended Error Code 8.
+ */
+static bool legacy_mce_is_memory_error(struct mce *m)
+{
+	return m->bank == 4 && XEC(m->status, 0x1f) == 8;
+}
+
+/*
+ * DRAM ECC errors are reported in Unified Memory Controllers with
+ * Extended Error Code 0.
+ */
+static bool smca_mce_is_memory_error(struct mce *m)
 {
 	enum smca_bank_types bank_type;
-	/* ErrCodeExt[20:16] */
-	u8 xec = (m->status >> 16) & 0x1f;
+
+	if (XEC(m->status, 0x3f))
+		return false;
 
 	bank_type = smca_get_bank_type(m->extcpu, m->bank);
-	if (mce_flags.smca)
-		return (bank_type == SMCA_UMC || bank_type == SMCA_UMC_V2) && xec == 0x0;
 
-	return m->bank == 4 && xec == 0x8;
+	return bank_type == SMCA_UMC || bank_type == SMCA_UMC_V2;
+}
+
+bool amd_mce_is_memory_error(struct mce *m)
+{
+	if (mce_flags.smca)
+		return smca_mce_is_memory_error(m);
+	else
+		return legacy_mce_is_memory_error(m);
 }
 
 static void __log_error(unsigned int bank, u64 status, u64 addr, u64 misc)