[PATCH v9 3/3] x86/cpu: Do a sanity check on required feature bits

[Maciej Wieczor-Retman]

From: Maciej Wieczor-Retman <maciej.wieczor-retman@xxxxxxxxx>

After CPU identification concludes, do a sanity check by comparing the
final x86_capability bitmask with the pre-defined required feature bits.

Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@xxxxxxxxx>
Acked-by: H. Peter Anvin (Intel) <hpa@xxxxxxxxx>
---
Changelog v9:
- REQUIRED_MASK_INITIALIZER -> REQUIRED_MASK_INIT
- Redo the comments.
- Fix reverse xmas order.
- Inside for_each_set_bit: (void *) -> (unsigned long *).
- 16 -> X86_CAP_BUF_SIZE.

Changelog v6:
- Add Peter's acked-by tag.
- Rename patch subject to imperative form.
- Add a char buffer to the x86_cap_name() call.

 arch/x86/kernel/cpu/common.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index cfffbbda3d95..43ee2d55a708 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -2003,6 +2003,34 @@ const char *x86_cap_name(unsigned int bit, char *buf)
 	return buf;
 }
 
+/*
+ * As a sanity check compare the final x86_capability bitmask with the initial
+ * predefined required feature bits. In case of a mismatch emit a warning with
+ * all the missing feature names or X86_FEATURE_* numerals.
+ */
+static void verify_required_features(const struct cpuinfo_x86 *c)
+{
+	u32 missing[NCAPINTS] = REQUIRED_MASK_INIT;
+	char cap_buf[X86_CAP_BUF_SIZE];
+	unsigned int i;
+	u32 error = 0;
+
+	for (i = 0; i < NCAPINTS; i++) {
+		missing[i] &= ~c->x86_capability[i];
+		error |= missing[i];
+	}
+
+	if (!error)
+		return;
+
+	/* At least one required feature is missing */
+	pr_warn("cpu %d: missing required feature(s):", c->cpu_index);
+	for_each_set_bit(i, (unsigned long *)missing, NCAPINTS << 5)
+		pr_cont(" %s", x86_cap_name(i, cap_buf));
+	pr_cont("\n");
+	add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
+}
+
 /*
  * This does the hard work of actually picking apart the CPU stuff...
  */
@@ -2132,6 +2160,8 @@ static void identify_cpu(struct cpuinfo_x86 *c)
 	mcheck_cpu_init(c);
 
 	numa_add_cpu(smp_processor_id());
+
+	verify_required_features(c);
 }
 
 /*
-- 
2.53.0