Xen/gnttab: introduce common INVALID_GRANT_{HANDLE,REF}

It's not helpful if every driver has to cook its own. Generalize
xenbus'es INVALID_GRANT_HANDLE and pcifront's INVALID_GRANT_REF (which
shouldn't have expanded to zero to begin with). Use the constants in
p2m.c and gntdev.c right away, and update field types where necessary so
they would match with the constants' types (albeit without touching
struct ioctl_gntdev_grant_ref's ref field, as that's part of the public
interface of the kernel and would require introducing a dependency on
Xen's grant_table.h public header).

Signed-off-by: Jan Beulich <[e-mail]>
Reviewed-by: Juergen Gross <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Boris Ostrovsky <[e-mail]>

arch/arm/xen/p2m.c

···
 
 #include <xen/xen.h>
 #include <xen/interface/memory.h>
+#include <xen/grant_table.h>
 #include <xen/page.h>
 #include <xen/swiotlb-xen.h>
 
···
 		map_ops[i].status = GNTST_general_error;
 		unmap.host_addr = map_ops[i].host_addr,
 		unmap.handle = map_ops[i].handle;
-		map_ops[i].handle = ~0;
+		map_ops[i].handle = INVALID_GRANT_HANDLE;
 		if (map_ops[i].flags & GNTMAP_device_map)
 			unmap.dev_bus_addr = map_ops[i].dev_bus_addr;
 		else

arch/x86/xen/p2m.c

···
 		map_ops[i].status = GNTST_general_error;
 		unmap[0].host_addr = map_ops[i].host_addr,
 		unmap[0].handle = map_ops[i].handle;
-		map_ops[i].handle = ~0;
+		map_ops[i].handle = INVALID_GRANT_HANDLE;
 		if (map_ops[i].flags & GNTMAP_device_map)
 			unmap[0].dev_bus_addr = map_ops[i].dev_bus_addr;
 		else
···
 			kmap_ops[i].status = GNTST_general_error;
 			unmap[1].host_addr = kmap_ops[i].host_addr,
 			unmap[1].handle = kmap_ops[i].handle;
-			kmap_ops[i].handle = ~0;
+			kmap_ops[i].handle = INVALID_GRANT_HANDLE;
 			if (kmap_ops[i].flags & GNTMAP_device_map)
 				unmap[1].dev_bus_addr = kmap_ops[i].dev_bus_addr;
 			else

drivers/pci/xen-pcifront.c

···
 #include <xen/platform_pci.h>
 
 #include <asm/xen/swiotlb-xen.h>
-#define INVALID_GRANT_REF (0)
+
 #define INVALID_EVTCHN    (-1)
 
 struct pci_bus_entry {
···
 	struct list_head root_buses;
 
 	int evtchn;
-	int gnt_ref;
+	grant_ref_t gnt_ref;
 
 	int irq;
 

drivers/xen/gntdev.c

···
 		goto err;
 
 	for (i = 0; i < count; i++) {
-		add->map_ops[i].handle = -1;
-		add->unmap_ops[i].handle = -1;
+		add->map_ops[i].handle = INVALID_GRANT_HANDLE;
+		add->unmap_ops[i].handle = INVALID_GRANT_HANDLE;
 		if (use_ptemod) {
-			add->kmap_ops[i].handle = -1;
-			add->kunmap_ops[i].handle = -1;
+			add->kmap_ops[i].handle = INVALID_GRANT_HANDLE;
+			add->kunmap_ops[i].handle = INVALID_GRANT_HANDLE;
 		}
 	}
 
···
 			  map->grants[pgnr].ref,
 			  map->grants[pgnr].domid);
 	gnttab_set_unmap_op(&map->unmap_ops[pgnr], pte_maddr, flags,
-			    -1 /* handle */);
+			    INVALID_GRANT_HANDLE);
 	return 0;
 }
 
···
 
 	if (!use_ptemod) {
 		/* Note: it could already be mapped */
-		if (map->map_ops[0].handle != -1)
+		if (map->map_ops[0].handle != INVALID_GRANT_HANDLE)
 			return 0;
 		for (i = 0; i < map->count; i++) {
 			unsigned long addr = (unsigned long)
···
 				map->grants[i].ref,
 				map->grants[i].domid);
 			gnttab_set_unmap_op(&map->unmap_ops[i], addr,
-				map->flags, -1 /* handle */);
+				map->flags, INVALID_GRANT_HANDLE);
 		}
 	} else {
 		/*
···
 				map->grants[i].ref,
 				map->grants[i].domid);
 			gnttab_set_unmap_op(&map->kunmap_ops[i], address,
-				flags, -1);
+				flags, INVALID_GRANT_HANDLE);
 		}
 	}
 
···
 		pr_debug("unmap handle=%d st=%d\n",
 			map->unmap_ops[offset+i].handle,
 			map->unmap_ops[offset+i].status);
-		map->unmap_ops[offset+i].handle = -1;
+		map->unmap_ops[offset+i].handle = INVALID_GRANT_HANDLE;
 	}
 	return err;
 }
···
 	 * already unmapped some of the grants. Only unmap valid ranges.
 	 */
 	while (pages && !err) {
-		while (pages && map->unmap_ops[offset].handle == -1) {
+		while (pages &&
+		       map->unmap_ops[offset].handle == INVALID_GRANT_HANDLE) {
 			offset++;
 			pages--;
 		}
 		range = 0;
 		while (range < pages) {
-			if (map->unmap_ops[offset+range].handle == -1)
+			if (map->unmap_ops[offset + range].handle ==
+			    INVALID_GRANT_HANDLE)
 				break;
 			range++;
 		}

include/xen/grant_table.h

···
 #include <linux/page-flags.h>
 #include <linux/kernel.h>
 
+/*
+ * Technically there's no reliably invalid grant reference or grant handle,
+ * so pick the value that is the most unlikely one to be observed valid.
+ */
+#define INVALID_GRANT_REF          ((grant_ref_t)-1)
+#define INVALID_GRANT_HANDLE       ((grant_handle_t)-1)
+
 #define GNTTAB_RESERVED_XENSTORE 1
 
 /* NR_GRANT_FRAMES must be less than or equal to that configured in Xen */

include/xen/xenbus.h

···
 
 #define XENBUS_MAX_RING_GRANT_ORDER 4
 #define XENBUS_MAX_RING_GRANTS      (1U << XENBUS_MAX_RING_GRANT_ORDER)
-#define INVALID_GRANT_HANDLE       (~0U)
 
 /* Register callback to watch this node. */
 struct xenbus_watch