[PATCH] x86/bugs: Remove X86_BUG_MMIO_UNKNOWN

[Borislav Petkov <bp@kernel.org>]

From: "Borislav Petkov (AMD)" <bp@alien8.de>

Whack this thing because:

- the "unknown" handling is done only for this vuln and not for the
  others

- it doesn't do anything besides reporting things differently. It
  doesn't apply any mitigations - it is simply causing unnecessary
  complications to the code which don't bring anything besides
  maintenance overhead to what is already a very nasty spaghetti pile

- all the currently unaffected CPUs can also be in "unknown" status so
  there's no need for special handling here

so get rid of it.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
---
 arch/x86/include/asm/cpufeatures.h       |  2 +-
 arch/x86/kernel/cpu/bugs.c               | 12 +-----------
 arch/x86/kernel/cpu/common.c             |  5 -----
 tools/arch/x86/include/asm/cpufeatures.h |  2 +-
 4 files changed, 3 insertions(+), 18 deletions(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 6c2c152d8a67..e8f8d43a3825 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -519,7 +519,7 @@
 #define X86_BUG_ITLB_MULTIHIT		X86_BUG(23) /* "itlb_multihit" CPU may incur MCE during certain page attribute changes */
 #define X86_BUG_SRBDS			X86_BUG(24) /* "srbds" CPU may leak RNG bits if not mitigated */
 #define X86_BUG_MMIO_STALE_DATA		X86_BUG(25) /* "mmio_stale_data" CPU is affected by Processor MMIO Stale Data vulnerabilities */
-#define X86_BUG_MMIO_UNKNOWN		X86_BUG(26) /* "mmio_unknown" CPU is too old and its MMIO Stale Data status is unknown */
+/* unused, was #define X86_BUG_MMIO_UNKNOWN		X86_BUG(26) "mmio_unknown" CPU is too old and its MMIO Stale Data status is unknown */
 #define X86_BUG_RETBLEED		X86_BUG(27) /* "retbleed" CPU is affected by RETBleed */
 #define X86_BUG_EIBRS_PBRSB		X86_BUG(28) /* "eibrs_pbrsb" EIBRS is vulnerable to Post Barrier RSB Predictions */
 #define X86_BUG_SMT_RSB			X86_BUG(29) /* "smt_rsb" CPU is vulnerable to Cross-Thread Return Address Predictions */
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 4f6bda8b5361..0e120da17414 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -427,7 +427,6 @@ static const char * const mmio_strings[] = {
 static void __init mmio_select_mitigation(void)
 {
 	if (!boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA) ||
-	     boot_cpu_has_bug(X86_BUG_MMIO_UNKNOWN) ||
 	     cpu_mitigations_off()) {
 		mmio_mitigation = MMIO_MITIGATION_OFF;
 		return;
@@ -590,8 +589,6 @@ static void __init md_clear_update_mitigation(void)
 		pr_info("TAA: %s\n", taa_strings[taa_mitigation]);
 	if (boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA))
 		pr_info("MMIO Stale Data: %s\n", mmio_strings[mmio_mitigation]);
-	else if (boot_cpu_has_bug(X86_BUG_MMIO_UNKNOWN))
-		pr_info("MMIO Stale Data: Unknown: No mitigations\n");
 	if (boot_cpu_has_bug(X86_BUG_RFDS))
 		pr_info("Register File Data Sampling: %s\n", rfds_strings[rfds_mitigation]);
 }
@@ -2780,9 +2777,6 @@ static ssize_t tsx_async_abort_show_state(char *buf)
 
 static ssize_t mmio_stale_data_show_state(char *buf)
 {
-	if (boot_cpu_has_bug(X86_BUG_MMIO_UNKNOWN))
-		return sysfs_emit(buf, "Unknown: No mitigations\n");
-
 	if (mmio_mitigation == MMIO_MITIGATION_OFF)
 		return sysfs_emit(buf, "%s\n", mmio_strings[mmio_mitigation]);
 
@@ -2967,7 +2961,6 @@ static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr
 		return srbds_show_state(buf);
 
 	case X86_BUG_MMIO_STALE_DATA:
-	case X86_BUG_MMIO_UNKNOWN:
 		return mmio_stale_data_show_state(buf);
 
 	case X86_BUG_RETBLEED:
@@ -3036,10 +3029,7 @@ ssize_t cpu_show_srbds(struct device *dev, struct device_attribute *attr, char *
 
 ssize_t cpu_show_mmio_stale_data(struct device *dev, struct device_attribute *attr, char *buf)
 {
-	if (boot_cpu_has_bug(X86_BUG_MMIO_UNKNOWN))
-		return cpu_show_common(dev, attr, buf, X86_BUG_MMIO_UNKNOWN);
-	else
-		return cpu_show_common(dev, attr, buf, X86_BUG_MMIO_STALE_DATA);
+	return cpu_show_common(dev, attr, buf, X86_BUG_MMIO_STALE_DATA);
 }
 
 ssize_t cpu_show_retbleed(struct device *dev, struct device_attribute *attr, char *buf)
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 079ded4eeb86..d7fe0fdb2cfa 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1402,15 +1402,10 @@ static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c)
 	 * Affected CPU list is generally enough to enumerate the vulnerability,
 	 * but for virtualization case check for ARCH_CAP MSR bits also, VMM may
 	 * not want the guest to enumerate the bug.
-	 *
-	 * Set X86_BUG_MMIO_UNKNOWN for CPUs that are neither in the blacklist,
-	 * nor in the whitelist and also don't enumerate MSR ARCH_CAP MMIO bits.
 	 */
 	if (!arch_cap_mmio_immune(x86_arch_cap_msr)) {
 		if (cpu_matches(cpu_vuln_blacklist, MMIO))
 			setup_force_cpu_bug(X86_BUG_MMIO_STALE_DATA);
-		else if (!cpu_matches(cpu_vuln_whitelist, NO_MMIO))
-			setup_force_cpu_bug(X86_BUG_MMIO_UNKNOWN);
 	}
 
 	if (!cpu_has(c, X86_FEATURE_BTC_NO)) {
diff --git a/tools/arch/x86/include/asm/cpufeatures.h b/tools/arch/x86/include/asm/cpufeatures.h
index 9e3fa7942e7d..e88500d90309 100644
--- a/tools/arch/x86/include/asm/cpufeatures.h
+++ b/tools/arch/x86/include/asm/cpufeatures.h
@@ -508,7 +508,7 @@
 #define X86_BUG_ITLB_MULTIHIT		X86_BUG(23) /* "itlb_multihit" CPU may incur MCE during certain page attribute changes */
 #define X86_BUG_SRBDS			X86_BUG(24) /* "srbds" CPU may leak RNG bits if not mitigated */
 #define X86_BUG_MMIO_STALE_DATA		X86_BUG(25) /* "mmio_stale_data" CPU is affected by Processor MMIO Stale Data vulnerabilities */
-#define X86_BUG_MMIO_UNKNOWN		X86_BUG(26) /* "mmio_unknown" CPU is too old and its MMIO Stale Data status is unknown */
+/* unused, was #define X86_BUG_MMIO_UNKNOWN		X86_BUG(26) * "mmio_unknown" CPU is too old and its MMIO Stale Data status is unknown */
 #define X86_BUG_RETBLEED		X86_BUG(27) /* "retbleed" CPU is affected by RETBleed */
 #define X86_BUG_EIBRS_PBRSB		X86_BUG(28) /* "eibrs_pbrsb" EIBRS is vulnerable to Post Barrier RSB Predictions */
 #define X86_BUG_SMT_RSB			X86_BUG(29) /* "smt_rsb" CPU is vulnerable to Cross-Thread Return Address Predictions */
-- 
2.43.0