Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 4407204c authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

perf, x86: Detect broken BIOSes that corrupt the PMU 



Some BIOSes use PMU resources, which can cause various bugs:

 - Non-working or erratic PMU based statistics - the PMU can end up
   counting the wrong thing, resulting in misleading statistics

 - Profiling can stop working or it can profile the wrong thing

 - A non-working or erratic NMI watchdog that cannot be relied on

 - The kernel may disturb whatever thing the BIOS tries to use the
   PMU for - possibly causing hardware malfunction in extreme cases.

 - ... and other forms of potential misbehavior

Various forms of such misbehavior has been observed in practice - there are
BIOSes that just corrupt the PMU state, consequences be damned.

The PMU is a CPU resource that is handled by the kernel and the BIOS
stealing+corrupting it is not acceptable nor robust, so we detect it,
warn about it and further refuse to touch the PMU ourselves.

Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Jason Wessel <jason.wessel@windriver.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
LKML-Reference: <new-submission>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 006b20fe

arch/x86/kernel/cpu/perf_event.c

+42 −6
Original line number Diff line number Diff line
@@ -375,15 +375,53 @@ static void release_pmc_hardware(void) {} 
static bool check_hw_exists(void)

{

	u64 val, val_new = 0;

	int ret = 0;

	int i, reg, ret = 0;



	/*

	 * Check to see if the BIOS enabled any of the counters, if so

	 * complain and bail.

	 */

	for (i = 0; i < x86_pmu.num_counters; i++) {

		reg = x86_pmu.eventsel + i;

		ret = rdmsrl_safe(reg, &val);

		if (ret)

			goto msr_fail;

		if (val & ARCH_PERFMON_EVENTSEL_ENABLE)

			goto bios_fail;

	}



	if (x86_pmu.num_counters_fixed) {

		reg = MSR_ARCH_PERFMON_FIXED_CTR_CTRL;

		ret = rdmsrl_safe(reg, &val);

		if (ret)

			goto msr_fail;

		for (i = 0; i < x86_pmu.num_counters_fixed; i++) {

			if (val & (0x03 << i*4))

				goto bios_fail;

		}

	}



	/*

	 * Now write a value and read it back to see if it matches,

	 * this is needed to detect certain hardware emulators (qemu/kvm)

	 * that don't trap on the MSR access and always return 0s.

	 */

	val = 0xabcdUL;

	ret |= checking_wrmsrl(x86_pmu.perfctr, val);

	ret = checking_wrmsrl(x86_pmu.perfctr, val);

	ret |= rdmsrl_safe(x86_pmu.perfctr, &val_new);

	if (ret || val != val_new)

		return false;

		goto msr_fail;



	return true;



bios_fail:

	printk(KERN_CONT "Broken BIOS detected, using software events only.\n");

	printk(KERN_ERR FW_BUG "the BIOS has corrupted hw-PMU resources (MSR %x is %Lx)\n", reg, val);

	return false;



msr_fail:

	printk(KERN_CONT "Broken PMU hardware detected, using software events only.\n");

	return false;

}



static void reserve_ds_buffers(void);
@@ -1378,10 +1416,8 @@ int __init init_hw_perf_events(void) 
	pmu_check_apic();



	/* sanity check that the hardware exists or is emulated */

	if (!check_hw_exists()) {

		pr_cont("Broken PMU hardware detected, software events only.\n");

	if (!check_hw_exists())

		return 0;

	}



	pr_cont("%s PMU driver.\n", x86_pmu.name);