powerpc/pseries/vas: Add VAS IRQ primary handler

Bugzilla: https://bugzilla.redhat.com/2130348

commit 89ed0b7
Author: Haren Myneni <haren@linux.ibm.com>
Date:   Sun Oct 9 20:41:25 2022 -0700

    powerpc/pseries/vas: Add VAS IRQ primary handler

    irq_default_primary_handler() can be used only with IRQF_ONESHOT
    flag, but the flag disables IRQ before executing the thread handler
    and enables it after the interrupt is handled. But this IRQ disable
    sets the VAS IRQ OFF state in the hypervisor. In case if NX faults
    during this window, the hypervisor will not deliver the fault
    interrupt to the partition and the user space may wait continuously
    for the CSB update. So use VAS specific IRQ handler instead of
    calling the default primary handler.

    Increment pending_faults counter in IRQ handler and the bottom
    thread handler will process all faults based on this counter.
    In case if the another interrupt is received while the thread is
    running, it will be processed using this counter. The synchronization
    of top and bottom handlers will be done with IRQTF_RUNTHREAD flag
    and will re-enter to bottom half if this flag is set.

    Signed-off-by: Haren Myneni <haren@linux.ibm.com>
    Reviewed-by: Frederic Barrat <fbarrat@linux.ibm.com>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Link: https://lore.kernel.org/r/aaad8813b4762a6753cfcd0b605a7574a5192ec7.camel@linux.ibm.com

Signed-off-by: Mukesh Chaurasiya <mchauras@redhat.com>

Author: Mukesh Chaurasiya

arch/powerpc/platforms/pseries/vas.c

@@ -192,16 +192,41 @@ irqreturn_t pseries_vas_fault_thread_fn(int irq, void *data)
 	struct vas_user_win_ref *tsk_ref;
 	int rc;
 
-	rc = h_get_nx_fault(txwin->vas_win.winid, (u64)virt_to_phys(&crb));
-	if (!rc) {
-		tsk_ref = &txwin->vas_win.task_ref;
-		vas_dump_crb(&crb);
-		vas_update_csb(&crb, tsk_ref);
+	while (atomic_read(&txwin->pending_faults)) {
+		rc = h_get_nx_fault(txwin->vas_win.winid, (u64)virt_to_phys(&crb));
+		if (!rc) {
+			tsk_ref = &txwin->vas_win.task_ref;
+			vas_dump_crb(&crb);
+			vas_update_csb(&crb, tsk_ref);
+		}
+		atomic_dec(&txwin->pending_faults);
 	}
 
 	return IRQ_HANDLED;
 }
 
+/*
+ * irq_default_primary_handler() can be used only with IRQF_ONESHOT
+ * which disables IRQ before executing the thread handler and enables
+ * it after. But this disabling interrupt sets the VAS IRQ OFF
+ * state in the hypervisor. If the NX generates fault interrupt
+ * during this window, the hypervisor will not deliver this
+ * interrupt to the LPAR. So use VAS specific IRQ handler instead
+ * of calling the default primary handler.
+ */
+static irqreturn_t pseries_vas_irq_handler(int irq, void *data)
+{
+	struct pseries_vas_window *txwin = data;
+
+	/*
+	 * The thread hanlder will process this interrupt if it is
+	 * already running.
+	 */
+	atomic_inc(&txwin->pending_faults);
+
+	return IRQ_WAKE_THREAD;
+}
+
 /*
  * Allocate window and setup IRQ mapping.
  */
@@ -232,8 +257,9 @@ static int allocate_setup_window(struct pseries_vas_window *txwin,
 		goto out_irq;
 	}
 
-	rc = request_threaded_irq(txwin->fault_virq, NULL,
-				  pseries_vas_fault_thread_fn, IRQF_ONESHOT,
+	rc = request_threaded_irq(txwin->fault_virq,
+				  pseries_vas_irq_handler,
+				  pseries_vas_fault_thread_fn, 0,
 				  txwin->name, txwin);
 	if (rc) {
 		pr_err("VAS-Window[%d]: Request IRQ(%u) failed with %d\n",

arch/powerpc/platforms/pseries/vas.h

@@ -132,6 +132,7 @@ struct pseries_vas_window {
 	u64 flags;
 	char *name;
 	int fault_virq;
+	atomic_t pending_faults; /* Number of pending faults */
 };
 
 int sysfs_add_vas_caps(struct vas_cop_feat_caps *caps);