Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 5cb13cdc authored by Christian Borntraeger's avatar Christian Borntraeger Committed by Greg Kroah-Hartman
Browse files

s390/gmap: voluntarily schedule during key setting 



[ Upstream commit 6d5946274df1fff539a7eece458a43be733d1db8 ]

With large and many guest with storage keys it is possible to create
large latencies or stalls during initial key setting:

rcu: INFO: rcu_sched self-detected stall on CPU
rcu:   18-....: (2099 ticks this GP) idle=54e/1/0x4000000000000002 softirq=35598716/35598716 fqs=998
       (t=2100 jiffies g=155867385 q=20879)
Task dump for CPU 18:
CPU 1/KVM       R  running task        0 1030947 256019 0x06000004
Call Trace:
sched_show_task
rcu_dump_cpu_stacks
rcu_sched_clock_irq
update_process_times
tick_sched_handle
tick_sched_timer
__hrtimer_run_queues
hrtimer_interrupt
do_IRQ
ext_int_handler
ptep_zap_key

The mmap lock is held during the page walking but since this is a
semaphore scheduling is still possible. Same for the kvm srcu.
To minimize overhead do this on every segment table entry or large page.

Signed-off-by: default avatarChristian Borntraeger <borntraeger@linux.ibm.com>
Reviewed-by: default avatarAlexander Gordeev <agordeev@linux.ibm.com>
Reviewed-by: default avatarClaudio Imbrenda <imbrenda@linux.ibm.com>
Link: https://lore.kernel.org/r/20220530092706.11637-2-borntraeger@linux.ibm.com


Signed-off-by: default avatarChristian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: default avatarHeiko Carstens <hca@linux.ibm.com>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 69893d6d

arch/s390/mm/gmap.c

+14 −0
Original line number Diff line number Diff line
@@ -2579,6 +2579,18 @@ static int __s390_enable_skey_pte(pte_t *pte, unsigned long addr, 
	return 0;

}



/*

 * Give a chance to schedule after setting a key to 256 pages.

 * We only hold the mm lock, which is a rwsem and the kvm srcu.

 * Both can sleep.

 */

static int __s390_enable_skey_pmd(pmd_t *pmd, unsigned long addr,

				  unsigned long next, struct mm_walk *walk)

{

	cond_resched();

	return 0;

}



static int __s390_enable_skey_hugetlb(pte_t *pte, unsigned long addr,

				      unsigned long hmask, unsigned long next,

				      struct mm_walk *walk)
@@ -2601,12 +2613,14 @@ static int __s390_enable_skey_hugetlb(pte_t *pte, unsigned long addr, 
	end = start + HPAGE_SIZE - 1;

	__storage_key_init_range(start, end);

	set_bit(PG_arch_1, &page->flags);

	cond_resched();

	return 0;

}



static const struct mm_walk_ops enable_skey_walk_ops = {

	.hugetlb_entry		= __s390_enable_skey_hugetlb,

	.pte_entry		= __s390_enable_skey_pte,

	.pmd_entry		= __s390_enable_skey_pmd,

};



int s390_enable_skey(void)