linux-kernel - [PATCH 1/2] x86/mce: Simplify AMD severity grading logic

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Date:   Tue, 5 Apr 2022 13:32:13 -0500
From:   Carlos Bilbao <carlos.bilbao@....com>
To:     <bp@...en8.de>, <yazen.ghannam@....com>
CC:     <tglx@...utronix.de>, <mingo@...hat.com>,
        <dave.hansen@...ux.intel.com>, <x86@...nel.org>,
        <linux-kernel@...r.kernel.org>, <linux-edac@...r.kernel.org>,
        <bilbao@...edu>, Carlos Bilbao <carlos.bilbao@....com>
Subject: [PATCH 1/2] x86/mce: Simplify AMD severity grading logic

The MCE handler needs to understand the severity of the machine errors to
act accordingly. Simplify the AMD grading logic following a logic that
closely resembles the descriptions of the public PPR documents. This will
help include more fine-grained grading of errors in the future.

Signed-off-by: Carlos Bilbao <carlos.bilbao@....com>
---
 arch/x86/kernel/cpu/mce/severity.c | 104 +++++++++++------------------
 1 file changed, 39 insertions(+), 65 deletions(-)

diff --git a/arch/x86/kernel/cpu/mce/severity.c b/arch/x86/kernel/cpu/mce/severity.c
index 1add86935349..25aec5a27899 100644
--- a/arch/x86/kernel/cpu/mce/severity.c
+++ b/arch/x86/kernel/cpu/mce/severity.c
@@ -301,85 +301,59 @@ static noinstr int error_context(struct mce *m, struct pt_regs *regs)
 	}
 }
 
-static __always_inline int mce_severity_amd_smca(struct mce *m, enum context err_ctx)
-{
-	u64 mcx_cfg;
-
-	/*
-	 * We need to look at the following bits:
-	 * - "succor" bit (data poisoning support), and
-	 * - TCC bit (Task Context Corrupt)
-	 * in MCi_STATUS to determine error severity.
-	 */
-	if (!mce_flags.succor)
-		return MCE_PANIC_SEVERITY;
-
-	mcx_cfg = mce_rdmsrl(MSR_AMD64_SMCA_MCx_CONFIG(m->bank));
-
-	/* TCC (Task context corrupt). If set and if IN_KERNEL, panic. */
-	if ((mcx_cfg & MCI_CONFIG_MCAX) &&
-	    (m->status & MCI_STATUS_TCC) &&
-	    (err_ctx == IN_KERNEL))
-		return MCE_PANIC_SEVERITY;
-
-	 /* ...otherwise invoke hwpoison handler. */
-	return MCE_AR_SEVERITY;
-}
-
 /*
- * See AMD Error Scope Hierarchy table in a newer BKDG. For example
- * 49125_15h_Models_30h-3Fh_BKDG.pdf, section "RAS Features"
+ * See AMD PPR(s) section Machine Check Error Handling
  */
 static noinstr int mce_severity_amd(struct mce *m, struct pt_regs *regs, char **msg, bool is_excp)
 {
-	enum context ctx = error_context(m, regs);
-
-	/* Processor Context Corrupt, no need to fumble too much, die! */
-	if (m->status & MCI_STATUS_PCC)
-		return MCE_PANIC_SEVERITY;
+	int ret;
 
-	if (m->status & MCI_STATUS_UC) {
+	/*
+	 * Default return value: Action required, the error must be handled
+	 * immediately.
+	 */
+	ret = MCE_AR_SEVERITY;
 
-		if (ctx == IN_KERNEL)
-			return MCE_PANIC_SEVERITY;
+	/* Processor Context Corrupt, no need to fumble too much, die! */
+	if (m->status & MCI_STATUS_PCC) {
+		ret = MCE_PANIC_SEVERITY;
+		goto out_amd_severity;
+	}
 
-		/*
-		 * On older systems where overflow_recov flag is not present, we
-		 * should simply panic if an error overflow occurs. If
-		 * overflow_recov flag is present and set, then software can try
-		 * to at least kill process to prolong system operation.
-		 */
-		if (mce_flags.overflow_recov) {
-			if (mce_flags.smca)
-				return mce_severity_amd_smca(m, ctx);
-
-			/* kill current process */
-			return MCE_AR_SEVERITY;
-		} else {
-			/* at least one error was not logged */
-			if (m->status & MCI_STATUS_OVER)
-				return MCE_PANIC_SEVERITY;
-		}
-
-		/*
-		 * For any other case, return MCE_UC_SEVERITY so that we log the
-		 * error and exit #MC handler.
-		 */
-		return MCE_UC_SEVERITY;
+	if (m->status & MCI_STATUS_DEFERRED) {
+		ret = MCE_DEFERRED_SEVERITY;
+		goto out_amd_severity;
 	}
 
 	/*
-	 * deferred error: poll handler catches these and adds to mce_ring so
-	 * memory-failure can take recovery actions.
+	 * If the UC bit is not set, the system either corrected or deferred
+	 * the error. No action will be required after logging the error.
 	 */
-	if (m->status & MCI_STATUS_DEFERRED)
-		return MCE_DEFERRED_SEVERITY;
+	if (!(m->status & MCI_STATUS_UC)) {
+		ret = MCE_KEEP_SEVERITY;
+		goto out_amd_severity;
+	}
 
 	/*
-	 * corrected error: poll handler catches these and passes responsibility
-	 * of decoding the error to EDAC
+	 * On MCA Overflow, without the MCA Overflow recovery feature the
+	 * system will not be able to recover.
 	 */
-	return MCE_KEEP_SEVERITY;
+	if ((m->status & MCI_STATUS_OVER) && !mce_flags.overflow_recov) {
+		ret = MCE_PANIC_SEVERITY;
+		goto out_amd_severity;
+	}
+
+	if (!mce_flags.succor) {
+		ret = MCE_PANIC_SEVERITY;
+		goto out_amd_severity;
+	}
+
+	if (error_context(m, regs) == IN_KERNEL)
+		ret = MCE_PANIC_SEVERITY;
+
+out_amd_severity:
+
+	return ret;
 }
 
 static noinstr int mce_severity_intel(struct mce *m, struct pt_regs *regs, char **msg, bool is_excp)
-- 
2.31.1