[PATCH 4/4] x86/cpuid: check for dependencies violations in CPUID and attempt to fix them

[Maxim Levitsky]

Due to configuration bugs, sometimes a CPU feature is disabled in CPUID,
but not features that depend on it.

While the above is not supported, the kernel should try to not crash,
and clearing the dependent cpu caps is the best way to do it.

Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
---
 arch/x86/kernel/cpu/common.c     |  4 ++--
 arch/x86/kernel/cpu/cpuid-deps.c | 27 +++++++++++++++++++++++++--
 2 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 4cc79971d2d847..c83a8f447d6aed 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1469,7 +1469,7 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c)
 			this_cpu->c_early_init(c);
 
 		c->cpu_index = 0;
-		filter_cpuid_features(c, false);
+		filter_cpuid_features(c, true);
 
 		if (this_cpu->c_bsp_init)
 			this_cpu->c_bsp_init(c);
@@ -1757,7 +1757,7 @@ static void identify_cpu(struct cpuinfo_x86 *c)
 	 */
 
 	/* Filter out anything that depends on CPUID levels we don't have */
-	filter_cpuid_features(c, true);
+	filter_cpuid_features(c, false);
 
 	/* If the model name is still unset, do table lookup. */
 	if (!c->x86_model_id[0]) {
diff --git a/arch/x86/kernel/cpu/cpuid-deps.c b/arch/x86/kernel/cpu/cpuid-deps.c
index bcb091d02a754b..6d9c0e39851805 100644
--- a/arch/x86/kernel/cpu/cpuid-deps.c
+++ b/arch/x86/kernel/cpu/cpuid-deps.c
@@ -94,6 +94,11 @@ static inline void clear_feature(struct cpuinfo_x86 *c, unsigned int feature)
 		set_bit(feature, (unsigned long *)cpu_caps_cleared);
 }
 
+static inline bool test_feature(struct cpuinfo_x86 *c, unsigned int feature)
+{
+	return test_bit(feature, (unsigned long *)c->x86_capability);
+}
+
 /* Take the capabilities and the BUG bits into account */
 #define MAX_FEATURE_BITS ((NCAPINTS + NBUGINTS) * sizeof(u32) * 8)
 
@@ -127,6 +132,7 @@ void clear_cpu_cap(struct cpuinfo_x86 *c, unsigned int feature)
 	} while (changed);
 }
 
+
 void setup_clear_cpu_cap(unsigned int feature)
 {
 	clear_cpu_cap(&boot_cpu_data, feature);
@@ -137,6 +143,10 @@ void setup_clear_cpu_cap(unsigned int feature)
  * Some CPU features depend on higher CPUID levels, which may not always
  * be available due to CPUID level capping or broken virtualization
  * software.  Add those features to this table to auto-disable them.
+ *
+ * Also due to configuration bugs, some CPUID features might be present
+ * while CPUID features that they depend on are not present,
+ * e.g a AVX2 present but AVX is not present.
  */
 struct cpuid_dependent_feature {
 	u32 feature;
@@ -151,9 +161,10 @@ cpuid_dependent_features[] = {
 	{ 0, 0 }
 };
 
-void filter_cpuid_features(struct cpuinfo_x86 *c, bool warn)
+void filter_cpuid_features(struct cpuinfo_x86 *c, bool early)
 {
 	const struct cpuid_dependent_feature *df;
+	const struct cpuid_dep *d;
 
 	for (df = cpuid_dependent_features; df->feature; df++) {
 
@@ -172,10 +183,22 @@ void filter_cpuid_features(struct cpuinfo_x86 *c, bool warn)
 			continue;
 
 		clear_cpu_cap(c, df->feature);
-		if (!warn)
+		if (early)
 			continue;
 
 		pr_warn("CPU: CPU feature " X86_CAP_FMT " disabled, no CPUID level 0x%x\n",
 			x86_cap_flag(df->feature), df->level);
 	}
+
+	for (d = cpuid_deps; d->feature; d++) {
+
+		if (!test_feature(c, d->feature) || test_feature(c, d->depends))
+			continue;
+
+		clear_feature(c, d->feature);
+
+		pr_warn("CPU: CPU feature " X86_CAP_FMT " disabled, because it depends on "
+			X86_CAP_FMT " which is not supported in CPUID\n",
+			x86_cap_flag(d->feature), x86_cap_flag(d->depends));
+	}
 }
-- 
2.26.3