linux-toradex.git/arch/powerpc/kernel/time.c, branch v5.18

powerpc/time: Always set decrementer in timer_interrupt()

2022-04-21T06:10:56+00:00

This is a partial revert of commit 0faf20a1ad16 ("powerpc/64s/interrupt:
Don't enable MSR[EE] in irq handlers unless perf is in use").

Prior to that commit, we always set the decrementer in
timer_interrupt(), to clear the timer interrupt. Otherwise we could end
up continuously taking timer interrupts.

When high res timers are enabled there is no problem seen with leaving
the decrementer untouched in timer_interrupt(), because it will be
programmed via hrtimer_interrupt() -> tick_program_event() ->
clockevents_program_event() -> decrementer_set_next_event().

However with CONFIG_HIGH_RES_TIMERS=n or booting with highres=off, we
see a stall/lockup, because tick_nohz_handler() does not cause a
reprogram of the decrementer, leading to endless timer interrupts.
Example trace:

  [    1.898617][    T7] Freeing initrd memory: 2624K^M
  [   22.680919][    C1] rcu: INFO: rcu_sched detected stalls on CPUs/tasks:^M
  [   22.682281][    C1] rcu:     0-....: (25 ticks this GP) idle=073/0/0x1 softirq=10/16 fqs=1050 ^M
  [   22.682851][    C1]  (detected by 1, t=2102 jiffies, g=-1179, q=476)^M
  [   22.683649][    C1] Sending NMI from CPU 1 to CPUs 0:^M
  [   22.685252][    C0] NMI backtrace for cpu 0^M
  [   22.685649][    C0] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.16.0-rc2-00185-g0faf20a1ad16 #145^M
  [   22.686393][    C0] NIP:  c000000000016d64 LR: c000000000f6cca4 CTR: c00000000019c6e0^M
  [   22.686774][    C0] REGS: c000000002833590 TRAP: 0500   Not tainted  (5.16.0-rc2-00185-g0faf20a1ad16)^M
  [   22.687222][    C0] MSR:  8000000000009033   CR: 24000222  XER: 00000000^M
  [   22.688297][    C0] CFAR: c00000000000c854 IRQMASK: 0 ^M
  ...
  [   22.692637][    C0] NIP [c000000000016d64] arch_local_irq_restore+0x174/0x250^M
  [   22.694443][    C0] LR [c000000000f6cca4] __do_softirq+0xe4/0x3dc^M
  [   22.695762][    C0] Call Trace:^M
  [   22.696050][    C0] [c000000002833830] [c000000000f6cc80] __do_softirq+0xc0/0x3dc (unreliable)^M
  [   22.697377][    C0] [c000000002833920] [c000000000151508] __irq_exit_rcu+0xd8/0x130^M
  [   22.698739][    C0] [c000000002833950] [c000000000151730] irq_exit+0x20/0x40^M
  [   22.699938][    C0] [c000000002833970] [c000000000027f40] timer_interrupt+0x270/0x460^M
  [   22.701119][    C0] [c0000000028339d0] [c0000000000099a8] decrementer_common_virt+0x208/0x210^M

Possibly this should be fixed in the lowres timing code, but that would
be a generic change and could take some time and may not backport
easily, so for now make the programming of the decrementer unconditional
again in timer_interrupt() to avoid the stall/lockup.

Fixes: 0faf20a1ad16 ("powerpc/64s/interrupt: Don't enable MSR[EE] in irq handlers unless perf is in use")
Reported-by: Miguel Ojeda 
Signed-off-by: Michael Ellerman 
Reviewed-by: Nicholas Piggin 
Link: https://lore.kernel.org/r/20220420141657.771442-1-mpe@ellerman.id.au

powerpc/time: improve decrementer clockevent processing

2022-03-16T05:55:23+00:00

The stop/shutdown op should not use decrementer_set_next_event because
that sets decrementers_next_tb to now + decrementer_max, which means a
decrementer interrupt that occurs after that time will call the
clockevent event handler unexpectedly. Set next_tb to ~0 here to prevent
any clock event call. Init all clockevents to stopped.

Then the decrementer clockevent device always has event_handler set and
applicable because we know the clock event device was not stopped. So
make this call unconditional to show that it is always called. next_tb
need not be set to ~0 before the event handler is called because it will
stop the clockevent device if there is no other timer.

Finally, the timer broadcast interrupt should not modify next_tb because
it is not involved with the local decrementer clockevent on this CPU.

This doesn't fix a known bug, just tidies the code.

Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/20220124143930.3923442-3-npiggin@gmail.com

powerpc/time: Fix KVM host re-arming a timer beyond decrementer range

2022-03-16T05:55:23+00:00

If the next host timer is beyond decrementer range, timer_rearm_host_dec
will leave decrementer not programmed. This will not cause a problem for
the host it will just set the decrementer correctly when the decrementer
interrupt hits, it seems safer not to leave the next host decrementer
interrupt timing able to be influenced by a guest.

This code is only used in the P9 KVM paths so it's unlikely to be hit
practically unless large decrementer is force disabled in the host.

Fixes: 25aa145856cd ("powerpc/time: add API for KVM to re-arm the host timer/decrementer")
Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/20220124143930.3923442-2-npiggin@gmail.com

powerpc: Move C prototypes out of asm-prototypes.h

2022-03-08T11:06:25+00:00

We originally added asm-prototypes.h in commit 42f5b4cacd78 ("powerpc:
Introduce asm-prototypes.h"). It's purpose was for prototypes of C
functions that are only called from asm, in order to fix sparse
warnings about missing prototypes.

A few months later Nick added a different use case in
commit 4efca4ed05cb ("kbuild: modversions for EXPORT_SYMBOL() for asm")
for C prototypes for exported asm functions. This is basically the
inverse of our original usage.

Since then we've added various prototypes to asm-prototypes.h for both
reasons, meaning we now need to unstitch it all.

Dispatch prototypes of C functions into relevant headers and keep
only the prototypes for functions defined in assembly.

For the time being, leave prom_init() there because moving it
into asm/prom.h or asm/setup.h conflicts with
drivers/gpu/drm/nouveau/nvkm/subdev/bios/shadowrom.o
This will be fixed later by untaggling asm/pci.h and asm/prom.h
or by renaming the function in shadowrom.c

Signed-off-by: Christophe Leroy 
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/62d46904eca74042097acf4cb12c175e3067f3d1.1646413435.git.christophe.leroy@csgroup.eu

powerpc/mce: Avoid using irq_work_queue() in realmode

2022-03-07T13:05:00+00:00

In realmode mce handler we use irq_work_queue() to defer
the processing of mce events, irq_work_queue() can only
be called when translation is enabled because it touches
memory outside RMA, hence we enable translation before
calling irq_work_queue and disable on return, though it
is not safe to do in realmode.

To avoid this, program the decrementer and call the event
processing functions from timer handler.

Signed-off-by: Ganesh Goudar 
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/20220120121931.517974-1-ganeshgr@linux.ibm.com

powerpc/64s/interrupt: Fix decrementer storm

2022-01-25T05:50:10+00:00

The decrementer exception can fail to be cleared when the interrupt
returns in the case where the decrementer wraps with the next timer
still beyond decrementer_max. This results in a decrementer interrupt
storm. This is triggerable with small decrementer system with hard
and soft watchdogs disabled.

Fix this by always programming the decrementer if there was no timer.

Fixes: 0faf20a1ad16 ("powerpc/64s/interrupt: Don't enable MSR[EE] in irq handlers unless perf is in use")
Reported-by: Alexey Kardashevskiy 
Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/20220124143930.3923442-1-npiggin@gmail.com

powerpc/64s/interrupt: Don't enable MSR[EE] in irq handlers unless perf is in use

2021-12-16T10:31:45+00:00

Enabling MSR[EE] in interrupt handlers while interrupts are still soft
masked allows PMIs to profile interrupt handlers to some degree, beyond
what SIAR latching allows.

When perf is not being used, this is almost useless work. It requires an
extra mtmsrd in the irq handler, and it also opens the door to masked
interrupts hitting and requiring replay, which is more expensive than
just taking them directly. This effect can be noticable in high IRQ
workloads.

Avoid enabling MSR[EE] unless perf is currently in use. This saves about
60 cycles (or 8%) on a simple decrementer interrupt microbenchmark.
Replayed interrupts drop from 1.4% of all interrupts taken, to 0.003%.

This does prevent the soft-nmi interrupt being taken in these handlers,
but that's not too reliable anyway. The SMP watchdog will continue to be
the reliable way to catch lockups.

Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/20210922145452.352571-5-npiggin@gmail.com

powerpc/config: Add CONFIG_BOOKE_OR_40x

2021-12-09T11:41:19+00:00

We have many functionnalities common to 40x and BOOKE, it leads to
many places with #if defined(CONFIG_BOOKE) || defined(CONFIG_40x).

We are going to add a few more with KUAP for booke/40x, so create
a new symbol which is defined when either BOOKE or 40x is defined.

Signed-off-by: Christophe Leroy 
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/9a3dbd60924cb25c9f944d3d8205ac5a0d15e229.1634627931.git.christophe.leroy@csgroup.eu

powerpc/time: add API for KVM to re-arm the host timer/decrementer

2021-11-24T10:08:57+00:00

Rather than have KVM look up the host timer and fiddle with the
irq-work internal details, have the powerpc/time.c code provide a
function for KVM to re-arm the Linux timer code when exiting a
guest.

This is implementation has an improvement over existing code of
marking a decrementer interrupt as soft-pending if a timer has
expired, rather than setting DEC to a -ve value, which tended to
cause host timers to take two interrupts (first hdec to exit the
guest, then the immediate dec).

Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/20211123095231.1036501-8-npiggin@gmail.com

KVM: PPC: Book3S HV P9: Use large decrementer for HDEC

2021-11-24T10:08:57+00:00

On processors that don't suppress the HDEC exceptions when LPCR[HDICE]=0,
this could help reduce needless guest exits due to leftover exceptions on
entering the guest.

Signed-off-by: Nicholas Piggin 
Reviewed-by: Alexey Kardashevskiy 
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/20211123095231.1036501-6-npiggin@gmail.com