As per the (somewhat recent) comment before the definition of
`__cpuidle`, the tag is like `noinstr` but also marks a function so it
can be identified by cpu_in_idle(). Let's add these markings to arm64
cpuidle functions

With this change we get useful backtraces like:

  NMI backtrace for cpu N skipped: idling at cpu_do_idle+0x94/0x98

instead of useless backtraces when dumping all processors using
nmi_cpu_backtrace().

NOTE: this patch won't make cpu_in_idle() work perfectly for arm64,
but it doesn't hurt and does catch some cases. Specifically an example
that wasn't caught in my testing looked like this:

 gic_cpu_sys_reg_init+0x1f8/0x314
 gic_cpu_pm_notifier+0x40/0x78
 raw_notifier_call_chain+0x5c/0x134
 cpu_pm_notify+0x38/0x64
 cpu_pm_exit+0x20/0x2c
 psci_enter_idle_state+0x48/0x70
 cpuidle_enter_state+0xb8/0x260
 cpuidle_enter+0x44/0x5c
 do_idle+0x188/0x30c

Acked-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Acked-by: Sumit Garg <sumit.garg@linaro.org>
Tested-by: Chen-Yu Tsai <wenst@chromium.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20230906090246.v13.2.I4baba13e220bdd24d11400c67f137c35f07f82c7@changeid
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Current arch_cpu_idle() is called with IRQs disabled, but will return
with IRQs enabled.

However, the very first thing the generic code does after calling
arch_cpu_idle() is raw_local_irq_disable(). This means that
architectures that can idle with IRQs disabled end up doing a
pointless 'enable-disable' dance.

Therefore, push this IRQ disabling into the idle function, meaning
that those architectures can avoid the pointless IRQ state flipping.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Tony Lindgren <tony@atomide.com>
Tested-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
Acked-by: Mark Rutland <mark.rutland@arm.com> [arm64]
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Guo Ren <guoren@kernel.org>
Acked-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20230112195540.618076436@infradead.org

The never-ending entry.S refactoring continues, putting us in a much
better place wrt compiler instrumentation whilst moving more of the code
into C.

* for-next/entry:
  arm64: idle: don't instrument idle code with KCOV
  arm64: entry: don't instrument entry code with KCOV
  arm64: entry: make NMI entry/exit functions static
  arm64: entry: split SDEI entry
  arm64: entry: split bad stack entry
  arm64: entry: fold el1_inv() into el1h_64_sync_handler()
  arm64: entry: handle all vectors with C
  arm64: entry: template the entry asm functions
  arm64: entry: improve bad_mode()
  arm64: entry: move bad_mode() to entry-common.c
  arm64: entry: consolidate EL1 exception returns
  arm64: entry: organise entry vectors consistently
  arm64: entry: organise entry handlers consistently
  arm64: entry: convert IRQ+FIQ handlers to C
  arm64: entry: add a call_on_irq_stack helper
  arm64: entry: move NMI preempt logic to C
  arm64: entry: move arm64_preempt_schedule_irq to entry-common.c
  arm64: entry: convert SError handlers to C
  arm64: entry: unmask IRQ+FIQ after EL0 handling
  arm64: remove redundant local_daif_mask() in bad_mode()

The low-level idle code in arch_cpu_idle() and its callees runs at a
time where where portions of the kernel environment aren't available.
For example, RCU may not be watching, and lockdep state may be
out-of-sync with the hardware. Due to this, it is not sound to
instrument this code.

We generally avoid instrumentation by marking the entry functions as
`noinstr`, but currently this doesn't inhibit KCOV instrumentation.
Prevent this by factoring these functions into a new idle.c so that we
can disable KCOV for the entire compilation unit, as is done for the
core idle code in kernel/sched/idle.c.

We'd like to keep instrumentation of the rest of process.c, and for the
existing code in cpuidle.c, so a new compilation unit is preferable. The
arch_cpu_idle_dead() function in process.c is a cpu hotplug function
that is safe to instrument, so it is left as-is in process.c.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Cc: James Morse <james.morse@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20210607094624.34689-21-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>