s390/mm: move pfault code to own C file

The pfault code has nothing to do with regular fault handling.

Therefore move it to an own C file. Also add an own pfault header
file. This way changes to setup.h don't cause a recompile of the
pfault code and vice versa.

Reviewed-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

3 files changed, 240 insertions, 228 deletions

diff --git a/arch/s390/mm/Makefile b/arch/s390/mm/Makefile
index d90db06a8af5..352ff520fd94 100644
--- a/arch/s390/mm/Makefile
+++ b/arch/s390/mm/Makefile
@@ -10,3 +10,4 @@ obj-$(CONFIG_CMM)		+= cmm.o
 obj-$(CONFIG_HUGETLB_PAGE)	+= hugetlbpage.o
 obj-$(CONFIG_PTDUMP_CORE)	+= dump_pagetables.o
 obj-$(CONFIG_PGSTE)		+= gmap.o
+obj-$(CONFIG_PFAULT)		+= pfault.o
diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
index 2f123429a291..b5e1bea9194c 100644
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c
@@ -43,8 +43,6 @@
 #include "../kernel/entry.h"
 
 #define __FAIL_ADDR_MASK -4096L
-#define __SUBCODE_MASK 0x0600
-#define __PF_RES_FIELD 0x8000000000000000ULL
 
 /*
  * Allocate private vm_fault_reason from top.  Please make sure it won't
@@ -583,232 +581,6 @@ void do_dat_exception(struct pt_regs *regs)
 }
 NOKPROBE_SYMBOL(do_dat_exception);
 
-#ifdef CONFIG_PFAULT 
-/*
- * 'pfault' pseudo page faults routines.
- */
-static int pfault_disable;
-
-static int __init nopfault(char *str)
-{
-	pfault_disable = 1;
-	return 1;
-}
-
-__setup("nopfault", nopfault);
-
-struct pfault_refbk {
-	u16 refdiagc;
-	u16 reffcode;
-	u16 refdwlen;
-	u16 refversn;
-	u64 refgaddr;
-	u64 refselmk;
-	u64 refcmpmk;
-	u64 reserved;
-} __attribute__ ((packed, aligned(8)));
-
-static struct pfault_refbk pfault_init_refbk = {
-	.refdiagc = 0x258,
-	.reffcode = 0,
-	.refdwlen = 5,
-	.refversn = 2,
-	.refgaddr = __LC_LPP,
-	.refselmk = 1ULL << 48,
-	.refcmpmk = 1ULL << 48,
-	.reserved = __PF_RES_FIELD
-};
-
-int pfault_init(void)
-{
-        int rc;
-
-	if (pfault_disable)
-		return -1;
-	diag_stat_inc(DIAG_STAT_X258);
-	asm volatile(
-		"	diag	%1,%0,0x258\n"
-		"0:	j	2f\n"
-		"1:	la	%0,8\n"
-		"2:\n"
-		EX_TABLE(0b,1b)
-		: "=d" (rc)
-		: "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	%0,0,0x258\n"
-		"0:	nopr	%%r7\n"
-		EX_TABLE(0b,0b)
-		: : "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);
-
-#endif /* CONFIG_PFAULT */
-
 #if IS_ENABLED(CONFIG_PGSTE)
 
 void do_secure_storage_access(struct pt_regs *regs)
diff --git a/arch/s390/mm/pfault.c b/arch/s390/mm/pfault.c
new file mode 100644
index 000000000000..5c0547f8d5ee
--- /dev/null
+++ b/arch/s390/mm/pfault.c
@@ -0,0 +1,239 @@
+// 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 0x8000000000000000ULL
+
+/*
+ * 'pfault' pseudo page faults routines.
+ */
+static int pfault_disable;
+
+static int __init nopfault(char *str)
+{
+	pfault_disable = 1;
+	return 1;
+}
+
+__setup("nopfault", nopfault);
+
+struct pfault_refbk {
+	u16 refdiagc;
+	u16 reffcode;
+	u16 refdwlen;
+	u16 refversn;
+	u64 refgaddr;
+	u64 refselmk;
+	u64 refcmpmk;
+	u64 reserved;
+} __attribute__ ((packed, aligned(8)));
+
+static struct pfault_refbk pfault_init_refbk = {
+	.refdiagc = 0x258,
+	.reffcode = 0,
+	.refdwlen = 5,
+	.refversn = 2,
+	.refgaddr = __LC_LPP,
+	.refselmk = 1ULL << 48,
+	.refcmpmk = 1ULL << 48,
+	.reserved = __PF_RES_FIELD
+};
+
+int __pfault_init(void)
+{
+        int rc;
+
+	if (pfault_disable)
+		return -1;
+	diag_stat_inc(DIAG_STAT_X258);
+	asm volatile(
+		"	diag	%1,%0,0x258\n"
+		"0:	j	2f\n"
+		"1:	la	%0,8\n"
+		"2:\n"
+		EX_TABLE(0b,1b)
+		: "=d" (rc)
+		: "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	%0,0,0x258\n"
+		"0:	nopr	%%r7\n"
+		EX_TABLE(0b,0b)
+		: : "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);