From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Tue, 17 Sep 2024 10:40:34 +0000 (+0200)
Subject: Merge tag 'x86-build-2024-09-17' of git://git.kernel.org/pub/scm/linux/kernel/git... 
X-Git-Url: https://repo.jachan.dev/J-linux.git/commitdiff_plain/5ba202a7c986fc58dd2fd1571c99667ab2699995?hp=-c

Merge tag 'x86-build-2024-09-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 build updates from Thomas Gleixner:
 "Updates for KCOV instrumentation on x86:

   - Prevent spurious KCOV coverage in common_interrupt()

   - Fixup the KCOV Makefile directive which got stale due to a source
     file rename

   - Exclude stack unwinding from KCOV as it creates large amounts of
     uninteresting coverage

   - Provide a self test to validate that KCOV coverage of the interrupt
     handling code starts not before preempt count got updated"

* tag 'x86-build-2024-09-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86: Ignore stack unwinding in KCOV
  module: Fix KCOV-ignored file name
  kcov: Add interrupt handling self test
  x86/entry: Remove unwanted instrumentation in common_interrupt()
---

5ba202a7c986fc58dd2fd1571c99667ab2699995
diff --combined kernel/kcov.c
index 274b6b7c718d,d9d4a0c04185..28a6be6e64fd
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@@ -11,6 -11,7 +11,7 @@@
  #include <linux/fs.h>
  #include <linux/hashtable.h>
  #include <linux/init.h>
+ #include <linux/jiffies.h>
  #include <linux/kmsan-checks.h>
  #include <linux/mm.h>
  #include <linux/preempt.h>
@@@ -161,15 -162,6 +162,15 @@@ static void kcov_remote_area_put(struc
  	kmsan_unpoison_memory(&area->list, sizeof(area->list));
  }
  
 +/*
 + * Unlike in_serving_softirq(), this function returns false when called during
 + * a hardirq or an NMI that happened in the softirq context.
 + */
 +static inline bool in_softirq_really(void)
 +{
 +	return in_serving_softirq() && !in_hardirq() && !in_nmi();
 +}
 +
  static notrace bool check_kcov_mode(enum kcov_mode needed_mode, struct task_struct *t)
  {
  	unsigned int mode;
@@@ -179,7 -171,7 +180,7 @@@
  	 * so we ignore code executed in interrupts, unless we are in a remote
  	 * coverage collection section in a softirq.
  	 */
 -	if (!in_task() && !(in_serving_softirq() && t->kcov_softirq))
 +	if (!in_task() && !(in_softirq_really() && t->kcov_softirq))
  		return false;
  	mode = READ_ONCE(t->kcov_mode);
  	/*
@@@ -858,7 -850,7 +859,7 @@@ void kcov_remote_start(u64 handle
  
  	if (WARN_ON(!kcov_check_handle(handle, true, true, true)))
  		return;
 -	if (!in_task() && !in_serving_softirq())
 +	if (!in_task() && !in_softirq_really())
  		return;
  
  	local_lock_irqsave(&kcov_percpu_data.lock, flags);
@@@ -1000,7 -992,7 +1001,7 @@@ void kcov_remote_stop(void
  	int sequence;
  	unsigned long flags;
  
 -	if (!in_task() && !in_serving_softirq())
 +	if (!in_task() && !in_softirq_really())
  		return;
  
  	local_lock_irqsave(&kcov_percpu_data.lock, flags);
@@@ -1067,6 -1059,32 +1068,32 @@@ u64 kcov_common_handle(void
  }
  EXPORT_SYMBOL(kcov_common_handle);
  
+ #ifdef CONFIG_KCOV_SELFTEST
+ static void __init selftest(void)
+ {
+ 	unsigned long start;
+ 
+ 	pr_err("running self test\n");
+ 	/*
+ 	 * Test that interrupts don't produce spurious coverage.
+ 	 * The coverage callback filters out interrupt code, but only
+ 	 * after the handler updates preempt count. Some code periodically
+ 	 * leaks out of that section and leads to spurious coverage.
+ 	 * It's hard to call the actual interrupt handler directly,
+ 	 * so we just loop here for a bit waiting for a timer interrupt.
+ 	 * We set kcov_mode to enable tracing, but don't setup the area,
+ 	 * so any attempt to trace will crash. Note: we must not call any
+ 	 * potentially traced functions in this region.
+ 	 */
+ 	start = jiffies;
+ 	current->kcov_mode = KCOV_MODE_TRACE_PC;
+ 	while ((jiffies - start) * MSEC_PER_SEC / HZ < 300)
+ 		;
+ 	current->kcov_mode = 0;
+ 	pr_err("done running self test\n");
+ }
+ #endif
+ 
  static int __init kcov_init(void)
  {
  	int cpu;
@@@ -1086,6 -1104,10 +1113,10 @@@
  	 */
  	debugfs_create_file_unsafe("kcov", 0600, NULL, NULL, &kcov_fops);
  
+ #ifdef CONFIG_KCOV_SELFTEST
+ 	selftest();
+ #endif
+ 
  	return 0;
  }
  
diff --combined lib/Kconfig.debug
index a40aa606cd04,270e367b3e6f..26354671b37d
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@@ -97,7 -97,7 +97,7 @@@ config BOOT_PRINTK_DELA
  	  using "boot_delay=N".
  
  	  It is likely that you would also need to use "lpj=M" to preset
 -	  the "loops per jiffie" value.
 +	  the "loops per jiffy" value.
  	  See a previous boot log for the "lpj" value to use for your
  	  system, and then set "lpj=M" before setting "boot_delay=N".
  	  NOTE:  Using this option may adversely affect SMP systems.
@@@ -2173,6 -2173,14 +2173,14 @@@ config KCOV_IRQ_AREA_SIZ
  	  soft interrupts. This specifies the size of those areas in the
  	  number of unsigned long words.
  
+ config KCOV_SELFTEST
+ 	bool "Perform short selftests on boot"
+ 	depends on KCOV
+ 	help
+ 	  Run short KCOV coverage collection selftests on boot.
+ 	  On test failure, causes the kernel to panic. Recommended to be
+ 	  enabled, ensuring critical functionality works as intended.
+ 
  menuconfig RUNTIME_TESTING_MENU
  	bool "Runtime Testing"
  	default y