Merge tag 'timers-core-2024-05-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull timers and timekeeping updates from Thomas Gleixner:
 "Core code:

   - Make timekeeping and VDSO time readouts resilent against math
     overflow:

     In guest context the kernel is prone to math overflow when the host
     defers the timer interrupt due to overload, malfunction or malice.

     This can be mitigated by checking the clocksource delta for the
     maximum deferrement which is readily available. If that value is
     exceeded then the code uses a slowpath function which can handle
     the multiplication overflow.

     This functionality is enabled unconditionally in the kernel, but
     made conditional in the VDSO code. The latter is conditional
     because it allows architectures to optimize the check so it is not
     causing performance regressions.

     On X86 this is achieved by reworking the existing check for
     negative TSC deltas as a negative delta obviously exceeds the
     maximum deferrement when it is evaluated as an unsigned value. That
     avoids two conditionals in the hotpath and allows to hide both the
     negative delta and the large delta handling in the same slow path.

   - Add an initial minimal ktime_t abstraction for Rust

   - The usual boring cleanups and enhancements

  Drivers:

   - Boring updates to device trees and trivial enhancements in various
     drivers"

* tag 'timers-core-2024-05-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (33 commits)
  clocksource/drivers/arm_arch_timer: Mark hisi_161010101_oem_info const
  clocksource/drivers/timer-ti-dm: Remove an unused field in struct dmtimer
  clocksource/drivers/renesas-ostm: Avoid reprobe after successful early probe
  clocksource/drivers/renesas-ostm: Allow OSTM driver to reprobe for RZ/V2H(P) SoC
  dt-bindings: timer: renesas: ostm: Document Renesas RZ/V2H(P) SoC
  rust: time: doc: Add missing C header links
  clocksource: Make the int help prompt unit readable in ncurses
  hrtimer: Rename __hrtimer_hres_active() to hrtimer_hres_active()
  timerqueue: Remove never used function timerqueue_node_expires()
  rust: time: Add Ktime
  vdso: Fix powerpc build U64_MAX undeclared error
  clockevents: Convert s[n]printf() to sysfs_emit()
  clocksource: Convert s[n]printf() to sysfs_emit()
  clocksource: Make watchdog and suspend-timing multiplication overflow safe
  timekeeping: Let timekeeping_cycles_to_ns() handle both under and overflow
  timekeeping: Make delta calculation overflow safe
  timekeeping: Prepare timekeeping_cycles_to_ns() for overflow safety
  timekeeping: Fold in timekeeping_delta_to_ns()
  timekeeping: Consolidate timekeeping helpers
  timekeeping: Refactor timekeeping helpers
  ...

rust/kernel/time.rs

@@ -4,6 +4,12 @@
 //!
 //! This module contains the kernel APIs related to time and timers that
 //! have been ported or wrapped for usage by Rust code in the kernel.
+//!
+//! C header: [`include/linux/jiffies.h`](srctree/include/linux/jiffies.h).
+//! C header: [`include/linux/ktime.h`](srctree/include/linux/ktime.h).
+
+/// The number of nanoseconds per millisecond.
+pub const NSEC_PER_MSEC: i64 = bindings::NSEC_PER_MSEC as i64;
 
 /// The time unit of Linux kernel. One jiffy equals (1/HZ) second.
 pub type Jiffies = core::ffi::c_ulong;
@@ -18,3 +24,60 @@ pub fn msecs_to_jiffies(msecs: Msecs) -> Jiffies {
     // matter what the argument is.
     unsafe { bindings::__msecs_to_jiffies(msecs) }
 }
+
+/// A Rust wrapper around a `ktime_t`.
+#[repr(transparent)]
+#[derive(Copy, Clone)]
+pub struct Ktime {
+    inner: bindings::ktime_t,
+}
+
+impl Ktime {
+    /// Create a `Ktime` from a raw `ktime_t`.
+    #[inline]
+    pub fn from_raw(inner: bindings::ktime_t) -> Self {
+        Self { inner }
+    }
+
+    /// Get the current time using `CLOCK_MONOTONIC`.
+    #[inline]
+    pub fn ktime_get() -> Self {
+        // SAFETY: It is always safe to call `ktime_get` outside of NMI context.
+        Self::from_raw(unsafe { bindings::ktime_get() })
+    }
+
+    /// Divide the number of nanoseconds by a compile-time constant.
+    #[inline]
+    fn divns_constant<const DIV: i64>(self) -> i64 {
+        self.to_ns() / DIV
+    }
+
+    /// Returns the number of nanoseconds.
+    #[inline]
+    pub fn to_ns(self) -> i64 {
+        self.inner
+    }
+
+    /// Returns the number of milliseconds.
+    #[inline]
+    pub fn to_ms(self) -> i64 {
+        self.divns_constant::<NSEC_PER_MSEC>()
+    }
+}
+
+/// Returns the number of milliseconds between two ktimes.
+#[inline]
+pub fn ktime_ms_delta(later: Ktime, earlier: Ktime) -> i64 {
+    (later - earlier).to_ms()
+}
+
+impl core::ops::Sub for Ktime {
+    type Output = Ktime;
+
+    #[inline]
+    fn sub(self, other: Ktime) -> Ktime {
+        Self {
+            inner: self.inner - other.inner,
+        }
+    }
+}