Merge tag 'x86_misc_for_v5.10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull misc x86 fixes fromm Borislav Petkov:

 - Ratelimit the message about writes to unrecognized MSRs so that they
   don't spam the console log (Chris Down)

 - Document how the /proc/cpuinfo machinery works for future reference
   (Kyung Min Park, Ricardo Neri and Dave Hansen)

 - Correct the current NMI's duration calculation (Libing Zhou)

* tag 'x86_misc_for_v5.10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/nmi: Fix nmi_handle() duration miscalculation
  Documentation/x86: Add documentation for /proc/cpuinfo feature flags
  x86/msr: Make source of unrecognised MSR writes unambiguous
  x86/msr: Prevent userspace MSR access from dominating the console

2 files changed, 17 insertions, 6 deletions

diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c
index 49dcfb85e773..c0d409810658 100644
--- a/arch/x86/kernel/msr.c
+++ b/arch/x86/kernel/msr.c
@@ -80,18 +80,30 @@ static ssize_t msr_read(struct file *file, char __user *buf,
 
 static int filter_write(u32 reg)
 {
+	/*
+	 * MSRs writes usually happen all at once, and can easily saturate kmsg.
+	 * Only allow one message every 30 seconds.
+	 *
+	 * It's possible to be smarter here and do it (for example) per-MSR, but
+	 * it would certainly be more complex, and this is enough at least to
+	 * avoid saturating the ring buffer.
+	 */
+	static DEFINE_RATELIMIT_STATE(fw_rs, 30 * HZ, 1);
+
 	switch (allow_writes) {
 	case MSR_WRITES_ON:  return 0;
 	case MSR_WRITES_OFF: return -EPERM;
 	default: break;
 	}
 
+	if (!__ratelimit(&fw_rs))
+		return 0;
+
 	if (reg == MSR_IA32_ENERGY_PERF_BIAS)
 		return 0;
 
-	pr_err_ratelimited("Write to unrecognized MSR 0x%x by %s\n"
-			   "Please report to x86@kernel.org\n",
-			   reg, current->comm);
+	pr_err("Write to unrecognized MSR 0x%x by %s (pid: %d). Please report to x86@kernel.org.\n",
+	       reg, current->comm, current->pid);
 
 	return 0;
 }
diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c
index 4fc9954a9560..47381666d6a5 100644
--- a/arch/x86/kernel/nmi.c
+++ b/arch/x86/kernel/nmi.c
@@ -102,7 +102,6 @@ fs_initcall(nmi_warning_debugfs);
 
 static void nmi_check_duration(struct nmiaction *action, u64 duration)
 {
-	u64 whole_msecs = READ_ONCE(action->max_duration);
 	int remainder_ns, decimal_msecs;
 
 	if (duration < nmi_longest_ns || duration < action->max_duration)
@@ -110,12 +109,12 @@ static void nmi_check_duration(struct nmiaction *action, u64 duration)
 
 	action->max_duration = duration;
 
-	remainder_ns = do_div(whole_msecs, (1000 * 1000));
+	remainder_ns = do_div(duration, (1000 * 1000));
 	decimal_msecs = remainder_ns / 1000;
 
 	printk_ratelimited(KERN_INFO
 		"INFO: NMI handler (%ps) took too long to run: %lld.%03d msecs\n",
-		action->handler, whole_msecs, decimal_msecs);
+		action->handler, duration, decimal_msecs);
 }
 
 static int nmi_handle(unsigned int type, struct pt_regs *regs)