diff options
Diffstat (limited to 'arch/s390/mm/pfault.c')
| -rw-r--r-- | arch/s390/mm/pfault.c | 248 |
1 files changed, 248 insertions, 0 deletions
diff --git a/arch/s390/mm/pfault.c b/arch/s390/mm/pfault.c new file mode 100644 index 0000000000..1aac13bb8f --- /dev/null +++ b/arch/s390/mm/pfault.c @@ -0,0 +1,248 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright IBM Corp. 1999, 2023 + */ + +#include <linux/cpuhotplug.h> +#include <linux/sched/task.h> +#include <linux/errno.h> +#include <linux/init.h> +#include <linux/irq.h> +#include <asm/asm-extable.h> +#include <asm/pfault.h> +#include <asm/diag.h> + +#define __SUBCODE_MASK 0x0600 +#define __PF_RES_FIELD 0x8000000000000000UL + +/* + * 'pfault' pseudo page faults routines. + */ +static int pfault_disable; + +static int __init nopfault(char *str) +{ + pfault_disable = 1; + return 1; +} +early_param("nopfault", nopfault); + +struct pfault_refbk { + u16 refdiagc; + u16 reffcode; + u16 refdwlen; + u16 refversn; + u64 refgaddr; + u64 refselmk; + u64 refcmpmk; + u64 reserved; +}; + +static struct pfault_refbk pfault_init_refbk = { + .refdiagc = 0x258, + .reffcode = 0, + .refdwlen = 5, + .refversn = 2, + .refgaddr = __LC_LPP, + .refselmk = 1UL << 48, + .refcmpmk = 1UL << 48, + .reserved = __PF_RES_FIELD +}; + +int __pfault_init(void) +{ + int rc = -EOPNOTSUPP; + + if (pfault_disable) + return rc; + diag_stat_inc(DIAG_STAT_X258); + asm volatile( + " diag %[refbk],%[rc],0x258\n" + "0: nopr %%r7\n" + EX_TABLE(0b, 0b) + : [rc] "+d" (rc) + : [refbk] "a" (&pfault_init_refbk), "m" (pfault_init_refbk) + : "cc"); + return rc; +} + +static struct pfault_refbk pfault_fini_refbk = { + .refdiagc = 0x258, + .reffcode = 1, + .refdwlen = 5, + .refversn = 2, +}; + +void __pfault_fini(void) +{ + if (pfault_disable) + return; + diag_stat_inc(DIAG_STAT_X258); + asm volatile( + " diag %[refbk],0,0x258\n" + "0: nopr %%r7\n" + EX_TABLE(0b, 0b) + : + : [refbk] "a" (&pfault_fini_refbk), "m" (pfault_fini_refbk) + : "cc"); +} + +static DEFINE_SPINLOCK(pfault_lock); +static LIST_HEAD(pfault_list); + +#define PF_COMPLETE 0x0080 + +/* + * The mechanism of our pfault code: if Linux is running as guest, runs a user + * space process and the user space process accesses a page that the host has + * paged out we get a pfault interrupt. + * + * This allows us, within the guest, to schedule a different process. Without + * this mechanism the host would have to suspend the whole virtual cpu until + * the page has been paged in. + * + * So when we get such an interrupt then we set the state of the current task + * to uninterruptible and also set the need_resched flag. Both happens within + * interrupt context(!). If we later on want to return to user space we + * recognize the need_resched flag and then call schedule(). It's not very + * obvious how this works... + * + * Of course we have a lot of additional fun with the completion interrupt (-> + * host signals that a page of a process has been paged in and the process can + * continue to run). This interrupt can arrive on any cpu and, since we have + * virtual cpus, actually appear before the interrupt that signals that a page + * is missing. + */ +static void pfault_interrupt(struct ext_code ext_code, + unsigned int param32, unsigned long param64) +{ + struct task_struct *tsk; + __u16 subcode; + pid_t pid; + + /* + * Get the external interruption subcode & pfault initial/completion + * signal bit. VM stores this in the 'cpu address' field associated + * with the external interrupt. + */ + subcode = ext_code.subcode; + if ((subcode & 0xff00) != __SUBCODE_MASK) + return; + inc_irq_stat(IRQEXT_PFL); + /* Get the token (= pid of the affected task). */ + pid = param64 & LPP_PID_MASK; + rcu_read_lock(); + tsk = find_task_by_pid_ns(pid, &init_pid_ns); + if (tsk) + get_task_struct(tsk); + rcu_read_unlock(); + if (!tsk) + return; + spin_lock(&pfault_lock); + if (subcode & PF_COMPLETE) { + /* signal bit is set -> a page has been swapped in by VM */ + if (tsk->thread.pfault_wait == 1) { + /* + * Initial interrupt was faster than the completion + * interrupt. pfault_wait is valid. Set pfault_wait + * back to zero and wake up the process. This can + * safely be done because the task is still sleeping + * and can't produce new pfaults. + */ + tsk->thread.pfault_wait = 0; + list_del(&tsk->thread.list); + wake_up_process(tsk); + put_task_struct(tsk); + } else { + /* + * Completion interrupt was faster than initial + * interrupt. Set pfault_wait to -1 so the initial + * interrupt doesn't put the task to sleep. + * If the task is not running, ignore the completion + * interrupt since it must be a leftover of a PFAULT + * CANCEL operation which didn't remove all pending + * completion interrupts. + */ + if (task_is_running(tsk)) + tsk->thread.pfault_wait = -1; + } + } else { + /* signal bit not set -> a real page is missing. */ + if (WARN_ON_ONCE(tsk != current)) + goto out; + if (tsk->thread.pfault_wait == 1) { + /* Already on the list with a reference: put to sleep */ + goto block; + } else if (tsk->thread.pfault_wait == -1) { + /* + * Completion interrupt was faster than the initial + * interrupt (pfault_wait == -1). Set pfault_wait + * back to zero and exit. + */ + tsk->thread.pfault_wait = 0; + } else { + /* + * Initial interrupt arrived before completion + * interrupt. Let the task sleep. + * An extra task reference is needed since a different + * cpu may set the task state to TASK_RUNNING again + * before the scheduler is reached. + */ + get_task_struct(tsk); + tsk->thread.pfault_wait = 1; + list_add(&tsk->thread.list, &pfault_list); +block: + /* + * Since this must be a userspace fault, there + * is no kernel task state to trample. Rely on the + * return to userspace schedule() to block. + */ + __set_current_state(TASK_UNINTERRUPTIBLE); + set_tsk_need_resched(tsk); + set_preempt_need_resched(); + } + } +out: + spin_unlock(&pfault_lock); + put_task_struct(tsk); +} + +static int pfault_cpu_dead(unsigned int cpu) +{ + struct thread_struct *thread, *next; + struct task_struct *tsk; + + spin_lock_irq(&pfault_lock); + list_for_each_entry_safe(thread, next, &pfault_list, list) { + thread->pfault_wait = 0; + list_del(&thread->list); + tsk = container_of(thread, struct task_struct, thread); + wake_up_process(tsk); + put_task_struct(tsk); + } + spin_unlock_irq(&pfault_lock); + return 0; +} + +static int __init pfault_irq_init(void) +{ + int rc; + + rc = register_external_irq(EXT_IRQ_CP_SERVICE, pfault_interrupt); + if (rc) + goto out_extint; + rc = pfault_init() == 0 ? 0 : -EOPNOTSUPP; + if (rc) + goto out_pfault; + irq_subclass_register(IRQ_SUBCLASS_SERVICE_SIGNAL); + cpuhp_setup_state_nocalls(CPUHP_S390_PFAULT_DEAD, "s390/pfault:dead", + NULL, pfault_cpu_dead); + return 0; + +out_pfault: + unregister_external_irq(EXT_IRQ_CP_SERVICE, pfault_interrupt); +out_extint: + pfault_disable = 1; + return rc; +} +early_initcall(pfault_irq_init); |