Comment 0 for bug 1975582

---Problem Description---
There can be rcu stalls when running lots of large guests with storage keys:

[1377614.579833] rcu: INFO: rcu_sched self-detected stall on CPU
[1377614.579845] rcu: 18-....: (2099 ticks this GP) idle=54e/1/0x4000000000000002 softirq=35598716/35598716 fqs=998
[1377614.579895] (t=2100 jiffies g=155867385 q=20879)
[1377614.579898] Task dump for CPU 18:
[1377614.579899] CPU 1/KVM R running task 0 1030947 256019 0x06000004
[1377614.579902] Call Trace:
[1377614.579912] ([<0000001f1f4b4f52>] show_stack+0x7a/0xc0)
[1377614.579918] [<0000001f1ec8e96c>] sched_show_task.part.0+0xdc/0x100
[1377614.579919] [<0000001f1f4b7248>] rcu_dump_cpu_stacks+0xc0/0x100
[1377614.579924] [<0000001f1ecdd10c>] rcu_sched_clock_irq+0x75c/0x980
[1377614.579926] [<0000001f1eceb26c>] update_process_times+0x3c/0x80
[1377614.579931] [<0000001f1ecfcfea>] tick_sched_handle.isra.0+0x4a/0x70
[1377614.579932] [<0000001f1ecfd28e>] tick_sched_timer+0x5e/0xc0
[1377614.579933] [<0000001f1ecec294>] __hrtimer_run_queues+0x114/0x2f0
[1377614.579935] [<0000001f1ececfdc>] hrtimer_interrupt+0x12c/0x2a0
[1377614.579938] [<0000001f1ebecb6a>] do_IRQ+0xaa/0xb0
[1377614.579942] [<0000001f1f4c6d08>] ext_int_handler+0x130/0x134
[1377614.579945] [<0000001f1ec0af10>] ptep_zap_key+0x40/0x60

Contact Information = <email address hidden>

---uname output---
     RELEASE: 5.4.0-90-generic
     VERSION: #101-Ubuntu SMP Fri Oct 15 19:59:45 UTC 2021

== Comment: #1 - Christian Borntraeger <email address hidden> - 2022-05-24 03:59:37 ==
This is a test patch that might address the rcu stalls.

== Comment: #2 - Christian Borntraeger <email address hidden> - 2022-05-24 04:00:22 ==
This is a 2nd patch that reduces the cost of key setting.