irqchip/gic-v3-its: Postpone LPI pending table freeing and memreserve

commit eba1e44b

 upstream

Memory used by the LPI tables have to be made persistent for kexec to have
a chance to work, as explained in [1]. If they have been made persistent
and we are booting into a kexec'd kernel, we also need to free the pages
that were preemptively allocated by the new kernel for those tables.

Both of those operations currently happen during its_cpu_init(), which
happens in a _STARTING (IOW atomic) cpuhp callback for secondary
CPUs. efi_mem_reserve_iomem() issues a GFP_ATOMIC allocation, which
unfortunately doesn't work under PREEMPT_RT (this ends up grabbing a
non-raw spinlock, which can sleep under PREEMPT_RT). Similarly, freeing the
pages ends up grabbing a sleepable spinlock.

Since the memreserve is only required by kexec, it doesn't have to be done
so early in the secondary boot process. Issue the reservation in a new
CPUHP_AP_ONLINE_DYN cpuhp callback, and piggy-back the page freeing on top
of it. A CPU gets to run the body of this new callback exactly once.

As kexec issues a machine_shutdown() prior to machine_kexec(), it will be
serialized vs a CPU being plugged to life by the hotplug machinery - either
the CPU will have been brought up and have had its redistributor's pending
table memreserved, or it never went online and will have its table
allocated by the new kernel.

[1]: https://lore.kernel.org/lkml/20180921195954.21574-1-marc.zyngier@arm.com/

Stable backport notes:
When rt kernel boots up, there is below calltrace
BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:969
in_atomic(): 1, irqs_disabled(): 128, non_block: 0, pid: 0, name: swapper/1
Preemption disabled at:
[<ffff800010089c14>] migrate_enable+0x44/0x1c8
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.10.140-rt73-yocto-preempt-rt #3
Hardware name: LS1028A RDB Board (DT)
Call trace:
 dump_backtrace+0x0/0x1e0
 show_stack+0x2c/0x38
 dump_stack+0xcc/0x104
 ___might_sleep+0x10c/0x178
 rt_spin_lock+0x2c/0x88
 __free_pages_ok+0x170/0x590
 __free_pages+0xcc/0xe8
 free_pages.part.123+0x3c/0x48
 free_pages+0x2c/0x38
 its_free_pending_table+0x68/0x78
 its_cpu_init+0x7c8/0xa78
 gic_starting_cpu+0x24/0x38
 cpuhp_invoke_callback+0xb8/0x890
 notify_cpu_starting+0xa8/0xe0
 secondary_start_kernel+0x138/0x1d0

In latest mainline kernel, this patch improved the LPI pending table
freeing and memreserve strategy, and also fix the calltrace issue.
Therefore, backport it and its fixing patches to stable kernel v5.15.

Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211027151506.2085066-3-valentin.schneider@arm.com
Cc: stable@vger.kernel.org
Signed-off-by: Meng Li <Meng.Li@windriver.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>