linux-kernel - [PATCH v5 2/3] x86/mce: Check for writes ignored in MCA

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Message-ID: <20220503032820.61667-3-Smita.KoralahalliChannabasappa@amd.com>
Date:   Mon, 2 May 2022 22:28:18 -0500
From:   Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
To:     <linux-edac@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <x86@...nel.org>
CC:     Tony Luck <tony.luck@...el.com>,
        Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>,
        <hpa@...or.com>, Yazen Ghannam <yazen.ghannam@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: [PATCH v5 2/3] x86/mce: Check for writes ignored in MCA_STATUS register

According to Section 2.1.16.3 under HWCR[McStatusWrEn] in "PPR for AMD
Family 19h, Model 01h, Revision B1 Processors - 55898 Rev 0.35 - Feb 5,
2021", the status register may sometimes enforce write ignored behavior
independent of the value of HWCR[McStatusWrEn] depending on the platform
settings.

Hence, evaluate for writes ignored for MCA_STATUS before doing hw error
injection. If true, return the appropriate error code to userspace.

Introduce "hw_injection_possible" flag to return early on subsequent
hw error injections.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537
Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
---
Link:
https://lkml.kernel.org/r/20220214233640.70510-2-Smita.KoralahalliChannabasappa@amd.com

v2:
	msr_ops -> mca_msr_reg().
	simulation -> injection.
	pr_info() -> pr_err().
	Aligned on ",".
v3:
	Removed "x86/mce: Use mca_msr_reg() in prepare_msrs()" patch.
	and made changes on the existing MCx_{STATUS, ADDR, MISC} macros.
v4:
	Simplified the code by just checking for writes ignored behavior in
	MCA_STATUS register.
	Introduced prepare_mca_status() and performed writes ignored checks
	inside the function.
	Rephrased error message.
v5:
	Replaced i_mce with inject_desc.
	Introduction of hw_injection_possible flag to return early if HW
	error injections are not possible.
---
 arch/x86/kernel/cpu/mce/inject.c   | 25 +++++++++++++++++++++++++
 arch/x86/kernel/cpu/mce/internal.h |  2 +-
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/mce/inject.c b/arch/x86/kernel/cpu/mce/inject.c
index 05581b718529..cce068a4478c 100644
--- a/arch/x86/kernel/cpu/mce/inject.c
+++ b/arch/x86/kernel/cpu/mce/inject.c
@@ -33,6 +33,8 @@
 
 #include "internal.h"
 
+static bool hw_injection_possible = true;
+
 /* Collect all the MCi_XXX settings */
 static struct inject_desc {
 	struct mce m;
@@ -474,11 +476,29 @@ static void toggle_nb_mca_mst_cpu(u16 nid)
 		       __func__, PCI_FUNC(F3->devfn), NBCFG);
 }
 
+static bool prepare_mca_status(void)
+{
+	u32 status_reg = mca_msr_reg(inj_desc.m.bank, MCA_STATUS);
+	u64 status_val = inj_desc.m.status;
+
+	wrmsrl(status_reg, status_val);
+	rdmsrl(status_reg, status_val);
+
+	return status_val == inj_desc.m.status;
+}
+
 static void prepare_msrs(void *unused)
 {
 	struct mce *m = &inj_desc.m;
 	u8 b = inj_desc.m.bank;
 
+	if (!prepare_mca_status()) {
+		pr_err("Platform does not allow error injection, try using APEI EINJ instead.\n");
+		inj_desc.err = -EINVAL;
+		hw_injection_possible = false;
+		return;
+	}
+
 	wrmsrl(MSR_IA32_MCG_STATUS, m->mcgstatus);
 
 	if (boot_cpu_has(X86_FEATURE_SMCA)) {
@@ -521,6 +541,11 @@ static int do_inject(void)
 		return 0;
 	}
 
+	if (!hw_injection_possible) {
+		pr_err("SW-only injection possible on this platform");
+		return -EINVAL;
+	}
+
 	/* prep MCE global settings for the injection */
 	mcg_status = MCG_STATUS_MCIP | MCG_STATUS_EIPV;
 
diff --git a/arch/x86/kernel/cpu/mce/internal.h b/arch/x86/kernel/cpu/mce/internal.h
index 4ae0e603f7fa..7e03f5b7f6bd 100644
--- a/arch/x86/kernel/cpu/mce/internal.h
+++ b/arch/x86/kernel/cpu/mce/internal.h
@@ -211,7 +211,7 @@ noinstr u64 mce_rdmsrl(u32 msr);
 
 static __always_inline u32 mca_msr_reg(int bank, enum mca_msr reg)
 {
-	if (mce_flags.smca) {
+	if (cpu_feature_enabled(X86_FEATURE_SMCA)) {
 		switch (reg) {
 		case MCA_CTL:	 return MSR_AMD64_SMCA_MCx_CTL(bank);
 		case MCA_ADDR:	 return MSR_AMD64_SMCA_MCx_ADDR(bank);
-- 
2.17.1