linux.git/arch/x86/kernel/tsc.c, branch v6.2

x86/tsc: Make art_related_clocksource static

2022-10-17T14:20:48+00:00

The symbol is not used outside of the file, so mark it static.

Fixes the following warning:

arch/x86/kernel/tsc.c:53:20: warning:
	symbol 'art_related_clocksource' was not declared. Should it be static?

Signed-off-by: Chen Lifu 
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/r/20220823021821.3052159-1-chenlifu@huawei.com

x86/tsc: Be consistent about use_tsc_delay()

2022-03-15T17:20:33+00:00

Currently loops_per_jiffy is set in tsc_early_init(), but then don't
switch to delay_tsc, with the result that delay_loop is used with
loops_per_jiffy set for delay_tsc.

Then in (late) tsc_init() lpj_fine is set (which is mostly unused) and
after which use_tsc_delay() is finally called.

Move both loops_per_jiffy and use_tsc_delay() into
tsc_enable_sched_clock() which is called the moment tsc_khz is
determined, be it early or late. Keeping the lot consistent.

Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lore.kernel.org/r/20220304152135.914397165@infradead.org
Signed-off-by: Greg Kroah-Hartman

x86/tsc: Disable clocksource watchdog for TSC on qualified platorms

2021-12-01T23:40:36+00:00

There are cases that the TSC clocksource is wrongly judged as unstable by
the clocksource watchdog mechanism which tries to validate the TSC against
HPET, PM_TIMER or jiffies. While there is hardly a general reliable way to
check the validity of a watchdog, Thomas Gleixner proposed [1]:

"I'm inclined to lift that requirement when the CPU has:

    1) X86_FEATURE_CONSTANT_TSC
    2) X86_FEATURE_NONSTOP_TSC
    3) X86_FEATURE_NONSTOP_TSC_S3
    4) X86_FEATURE_TSC_ADJUST
    5) At max. 4 sockets

 After two decades of horrors we're finally at a point where TSC seems
 to be halfway reliable and less abused by BIOS tinkerers. TSC_ADJUST
 was really key as we can now detect even small modifications reliably
 and the important point is that we can cure them as well (not pretty
 but better than all other options)."

As feature #3 X86_FEATURE_NONSTOP_TSC_S3 only exists on several generations
of Atom processorz, and is always coupled with X86_FEATURE_CONSTANT_TSC
and X86_FEATURE_NONSTOP_TSC, skip checking it, and also be more defensive
to use maximal 2 sockets.

The check is done inside tsc_init() before registering 'tsc-early' and
'tsc' clocksources, as there were cases that both of them had been
wrongly judged as unreliable.

For more background of tsc/watchdog, there is a good summary in [2]

[tglx} Update vs. jiffies:

  On systems where the only remaining clocksource aside of TSC is jiffies
  there is no way to make this work because that creates a circular
  dependency. Jiffies accuracy depends on not missing a periodic timer
  interrupt, which is not guaranteed. That could be detected by TSC, but as
  TSC is not trusted this cannot be compensated. The consequence is a
  circulus vitiosus which results in shutting down TSC and falling back to
  the jiffies clocksource which is even more unreliable.

[1]. https://lore.kernel.org/lkml/87eekfk8bd.fsf@nanos.tec.linutronix.de/
[2]. https://lore.kernel.org/lkml/87a6pimt1f.ffs@nanos.tec.linutronix.de/

[ tglx: Refine comment and amend changelog ]

Fixes: 6e3cd95234dc ("x86/hpet: Use another crystalball to evaluate HPET usability")
Suggested-by: Thomas Gleixner 
Signed-off-by: Feng Tang 
Signed-off-by: Thomas Gleixner 
Cc: "Paul E. McKenney" 
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20211117023751.24190-2-feng.tang@intel.com

clocksource: Reduce clocksource-skew threshold

2021-06-22T14:53:16+00:00

Currently, WATCHDOG_THRESHOLD is set to detect a 62.5-millisecond skew in
a 500-millisecond WATCHDOG_INTERVAL.  This requires that clocks be skewed
by more than 12.5% in order to be marked unstable.  Except that a clock
that is skewed by that much is probably destroying unsuspecting software
right and left.  And given that there are now checks for false-positive
skews due to delays between reading the two clocks, it should be possible
to greatly decrease WATCHDOG_THRESHOLD, at least for fine-grained clocks
such as TSC.

Therefore, add a new uncertainty_margin field to the clocksource structure
that contains the maximum uncertainty in nanoseconds for the corresponding
clock.  This field may be initialized manually, as it is for
clocksource_tsc_early and clocksource_jiffies, which is copied to
refined_jiffies.  If the field is not initialized manually, it will be
computed at clock-registry time as the period of the clock in question
based on the scale and freq parameters to __clocksource_update_freq_scale()
function.  If either of those two parameters are zero, the
tens-of-milliseconds WATCHDOG_THRESHOLD is used as a cowardly alternative
to dividing by zero.  No matter how the uncertainty_margin field is
calculated, it is bounded below by twice WATCHDOG_MAX_SKEW, that is, by 100
microseconds.

Note that manually initialized uncertainty_margin fields are not adjusted,
but there is a WARN_ON_ONCE() that triggers if any such field is less than
twice WATCHDOG_MAX_SKEW.  This WARN_ON_ONCE() is intended to discourage
production use of the one-nanosecond uncertainty_margin values that are
used to test the clock-skew code itself.

The actual clock-skew check uses the sum of the uncertainty_margin fields
of the two clocksource structures being compared.  Integer overflow is
avoided because the largest computed value of the uncertainty_margin
fields is one billion (10^9), and double that value fits into an
unsigned int.  However, if someone manually specifies (say) UINT_MAX,
they will get what they deserve.

Note that the refined_jiffies uncertainty_margin field is initialized to
TICK_NSEC, which means that skew checks involving this clocksource will
be sufficently forgiving.  In a similar vein, the clocksource_tsc_early
uncertainty_margin field is initialized to 32*NSEC_PER_MSEC, which
replicates the current behavior and allows custom setting if needed
in order to address the rare skews detected for this clocksource in
current mainline.

Suggested-by: Thomas Gleixner 
Signed-off-by: Paul E. McKenney 
Signed-off-by: Thomas Gleixner 
Acked-by: Feng Tang 
Link: https://lore.kernel.org/r/20210527190124.440372-4-paulmck@kernel.org

clocksource: Check per-CPU clock synchronization when marked unstable

2021-06-22T14:53:16+00:00

Some sorts of per-CPU clock sources have a history of going out of
synchronization with each other.  However, this problem has purportedy been
solved in the past ten years.  Except that it is all too possible that the
problem has instead simply been made less likely, which might mean that
some of the occasional "Marking clocksource 'tsc' as unstable" messages
might be due to desynchronization.  How would anyone know?

Therefore apply CPU-to-CPU synchronization checking to newly unstable
clocksource that are marked with the new CLOCK_SOURCE_VERIFY_PERCPU flag.
Lists of desynchronized CPUs are printed, with the caveat that if it
is the reporting CPU that is itself desynchronized, it will appear that
all the other clocks are wrong.  Just like in real life.

Reported-by: Chris Mason 
Signed-off-by: Paul E. McKenney 
Signed-off-by: Thomas Gleixner 
Acked-by: Feng Tang 
Link: https://lore.kernel.org/r/20210527190124.440372-2-paulmck@kernel.org

Merge tag 'x86_cleanups_for_v5.13' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2021-04-26T16:25:47+00:00

Pull misc x86 cleanups from Borislav Petkov:
 "Trivial cleanups and fixes all over the place"

* tag 'x86_cleanups_for_v5.13' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  MAINTAINERS: Remove me from IDE/ATAPI section
  x86/pat: Do not compile stubbed functions when X86_PAT is off
  x86/asm: Ensure asm/proto.h can be included stand-alone
  x86/platform/intel/quark: Fix incorrect kernel-doc comment syntax in files
  x86/msr: Make locally used functions static
  x86/cacheinfo: Remove unneeded dead-store initialization
  x86/process/64: Move cpu_current_top_of_stack out of TSS
  tools/turbostat: Unmark non-kernel-doc comment
  x86/syscalls: Fix -Wmissing-prototypes warnings from COND_SYSCALL()
  x86/fpu/math-emu: Fix function cast warning
  x86/msr: Fix wr/rdmsr_safe_regs_on_cpu() prototypes
  x86: Fix various typos in comments, take #2
  x86: Remove unusual Unicode characters from comments
  x86/kaslr: Return boolean values from a function returning bool
  x86: Fix various typos in comments
  x86/setup: Remove unused RESERVE_BRK_ARRAY()
  stacktrace: Move documentation for arch_stack_walk_reliable() to header
  x86: Remove duplicate TSC DEADLINE MSR definitions

x86: Fix various typos in comments

2021-03-18T14:31:53+00:00

Fix ~144 single-word typos in arch/x86/ code comments.

Doing this in a single commit should reduce the churn.

Signed-off-by: Ingo Molnar 
Cc: Borislav Petkov 
Cc: Thomas Gleixner 
Cc: Peter Zijlstra 
Cc: Paolo Bonzini 
Cc: Bjorn Helgaas 
Cc: linux-kernel@vger.kernel.org

x86/paravirt: Switch time pvops functions to use static_call()

2021-03-11T15:17:52+00:00

The time pvops functions are the only ones left which might be
used in 32-bit mode and which return a 64-bit value.

Switch them to use the static_call() mechanism instead of pvops, as
this allows quite some simplification of the pvops implementation.

Signed-off-by: Juergen Gross 
Signed-off-by: Borislav Petkov 
Acked-by: Peter Zijlstra (Intel) 
Link: https://lkml.kernel.org/r/20210311142319.4723-5-jgross@suse.com

x86/tsc: Use seqcount_latch_t

2020-09-10T09:19:29+00:00

Latch sequence counters have unique read and write APIs, and thus
seqcount_latch_t was recently introduced at seqlock.h.

Use that new data type instead of plain seqcount_t. This adds the
necessary type-safety and ensures that only latching-safe seqcount APIs
are to be used.

Signed-off-by: Ahmed S. Darwish 
[peterz: unwreck cyc2ns_read_begin()]
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lkml.kernel.org/r/20200827114044.11173-7-a.darwish@linutronix.de

x86/tsc: Add tsc_early_khz command line parameter

2020-05-21T21:07:00+00:00

Changing base clock frequency directly impacts TSC Hz but not CPUID.16h
value. An overclocked CPU supporting CPUID.16h and with partial CPUID.15h
support will set TSC KHZ according to "best guess" given by CPUID.16h
relying on tsc_refine_calibration_work to give better numbers later.
tsc_refine_calibration_work will refuse to do its work when the outcome is
off the early TSC KHZ value by more than 1% which is certain to happen on
an overclocked system.

Fix this by adding a tsc_early_khz command line parameter that makes the
kernel skip early TSC calibration and use the given value instead.

This allows the user to provide the expected TSC frequency that is closer
to reality than the one reported by the hardware, enabling
tsc_refine_calibration_work to do meaningful error checking.

[ tglx: Made the variable __initdata as it's only used on init and
        removed the error checking in the argument parser because
	kstrto*() only stores to the variable if the string is valid ]

Signed-off-by: Krzysztof Piecuch 
Signed-off-by: Thomas Gleixner 
Link: https://lkml.kernel.org/r/O2CpIOrqLZHgNRkfjRpz_LGqnc1ix_seNIiOCvHY4RHoulOVRo6kMXKuLOfBVTi0SMMevg6Go1uZ_cL9fLYtYdTRNH78ChaFaZyG3VAyYz8=@protonmail.com