[PATCH v3 02/14] KVM: s390: pv: avoid stall notifications for some UVCs

@@ -180,7 +180,7 @@ static int make_secure_pte(pte_t *ptep, unsigned long addr,
 {
 	pte_t entry = READ_ONCE(*ptep);
 	struct page *page;
-	int expected, rc = 0;
+	int expected, cc = 0;
 
 	if (!pte_present(entry))
 		return -ENXIO;

@@ -196,12 +196,25 @@ static int make_secure_pte(pte_t *ptep, unsigned long addr,
 	if (!page_ref_freeze(page, expected))
 		return -EBUSY;
 	set_bit(PG_arch_1, &page->flags);
-	rc = uv_call(0, (u64)uvcb);
+	/*
+	 * If the UVC does not succeed or fail immediately, we don't want to
+	 * loop for long, or we might get stall notifications.
+	 * On the other hand, this is a complex scenario and we are holding a lot of
+	 * locks, so we can't easily sleep and reschedule. We try only once,
+	 * and if the UVC returned busy or partial completion, we return
+	 * -EAGAIN and we let the callers deal with it.
+	 */
+	cc = __uv_call(0, (u64)uvcb);
 	page_ref_unfreeze(page, expected);
-	/* Return -ENXIO if the page was not mapped, -EINVAL otherwise */
-	if (rc)
-		rc = uvcb->rc == 0x10a ? -ENXIO : -EINVAL;
-	return rc;
+	/*
+	 * Return -ENXIO if the page was not mapped, -EINVAL for other errors.
+	 * If busy or partially completed, return -EAGAIN.
+	 */
+	if (cc == UVC_CC_OK)
+		return 0;
+	else if (cc == UVC_CC_BUSY || cc == UVC_CC_PARTIAL)
+		return -EAGAIN;
+	return uvcb->rc == 0x10a ? -ENXIO : -EINVAL;
 }
 
 /*

@@ -254,6 +267,10 @@ int gmap_make_secure(struct gmap *gmap, unsigned long gaddr, void *uvcb)
 	mmap_read_unlock(gmap->mm);
 
 	if (rc == -EAGAIN) {
+		/*
+		 * If we are here because the UVC returned busy or partial
+		 * completion, this is just a useless check, but it is safe.
+		 */
 		wait_on_page_writeback(page);
 	} else if (rc == -EBUSY) {
 		/*

@@ -196,7 +196,7 @@ int kvm_s390_pv_init_vm(struct kvm *kvm, u16 *rc, u16 *rrc)
 	uvcb.conf_base_stor_origin = (u64)kvm->arch.pv.stor_base;
 	uvcb.conf_virt_stor_origin = (u64)kvm->arch.pv.stor_var;
 
-	cc = uv_call(0, (u64)&uvcb);
+	cc = uv_call_sched(0, (u64)&uvcb);
 	*rc = uvcb.header.rc;
 	*rrc = uvcb.header.rrc;
 	KVM_UV_EVENT(kvm, 3, "PROTVIRT CREATE VM: handle %llx len %llx rc %x rrc %x",