[PATCH] xenpaging: handle GNTST_eagain in kernel drivers

[Olaf Hering <olaf@aepfle.de>]

Handle GNTST_eagain status from GNTTABOP_map_grant_ref and GNTTABOP_copy
operations properly to allow usage of xenpaging without causing crashes or data
corruption.

Remove the existing retry code from net_rx_action(), dispatch_rw_block_io(),
net_accel_map_grants_contig() and net_accel_map_iomem_page() and replace all
relevant HYPERVISOR_grant_table_op() calls with a retry loop.
This loop is implemented as a macro to allow different GNTTABOP_* args.
It will sleep up to 33 seconds and wait for the page to be paged in again.

All ->status checks were updated to use the GNTST_* namespace.
All return values are converted from GNTST_* namespace to 0/-EINVAL, since all
callers did not use the actual return value.

Signed-off-by: Olaf Hering <olaf@aepfle.de>

---
Compiled with x86_64 and i386 configs

 drivers/xen/blkback/blkback.c              |   57 ++++++-----------------------
 drivers/xen/blkback/common.h               |    2 -
 drivers/xen/blkback/interface.c            |   22 +++++------
 drivers/xen/blktap/blktap.c                |   29 ++++++--------
 drivers/xen/blktap/interface.c             |   22 +++++------
 drivers/xen/blktap2/device.c               |   34 ++++++++---------
 drivers/xen/core/gnttab.c                  |    4 +-
 drivers/xen/gntdev/gntdev.c                |   26 ++++++-------
 drivers/xen/netback/interface.c            |   26 ++++---------
 drivers/xen/netback/netback.c              |   52 +++++++-------------------
 drivers/xen/scsiback/interface.c           |   24 +++++-------
 drivers/xen/scsiback/scsiback.c            |   16 ++------
 drivers/xen/sfc_netutil/accel_util.c       |   41 +++++---------------
 drivers/xen/tpmback/interface.c            |   22 +++++------
 drivers/xen/tpmback/tpmback.c              |   22 +++--------
 drivers/xen/usbback/interface.c            |   25 ++++--------
 drivers/xen/usbback/usbback.c              |   16 ++------
 drivers/xen/xenbus/xenbus_backend_client.c |   27 ++++++-------
 include/xen/gnttab.h                       |   38 +++++++++++++++++++
 19 files changed, 204 insertions(+), 301 deletions(-)

--- linux-2.6.18-xen.hg.orig/drivers/xen/blkback/blkback.c
+++ linux-2.6.18-xen.hg/drivers/xen/blkback/blkback.c
@@ -107,7 +107,7 @@ static inline unsigned long vaddr(pendin
 
 
 static int do_block_io_op(blkif_t *blkif);
-static int dispatch_rw_block_io(blkif_t *blkif,
+static void dispatch_rw_block_io(blkif_t *blkif,
 				 blkif_request_t *req,
 				 pending_req_t *pending_req);
 static void make_response(blkif_t *blkif, u64 id,
@@ -312,13 +312,13 @@ static int do_block_io_op(blkif_t *blkif
 	blkif_request_t req;
 	pending_req_t *pending_req;
 	RING_IDX rc, rp;
-	int more_to_do = 0, ret;
+	int more_to_do = 0;
 
 	rc = blk_rings->common.req_cons;
 	rp = blk_rings->common.sring->req_prod;
 	rmb(); /* Ensure we see queued requests up to 'rp'. */
 
-	while ((rc != rp) || (blkif->is_suspended_req)) {
+	while ((rc != rp)) {
 
 		if (RING_REQUEST_CONS_OVERFLOW(&blk_rings->common, rc))
 			break;
@@ -335,14 +335,6 @@ static int do_block_io_op(blkif_t *blkif
 			break;
 		}
 
-        /* Handle the suspended request first, if one exists */
-        if(blkif->is_suspended_req)
-        {
-            memcpy(&req, &blkif->suspended_req, sizeof(req));
-            blkif->is_suspended_req = 0;
-            goto handle_request;
-        }
-
 		switch (blkif->blk_protocol) {
 		case BLKIF_PROTOCOL_NATIVE:
 			memcpy(&req, RING_GET_REQUEST(&blk_rings->native, rc), sizeof(req));
@@ -361,19 +353,17 @@ static int do_block_io_op(blkif_t *blkif
 		/* Apply all sanity checks to /private copy/ of request. */
 		barrier();
 
-handle_request:
-        ret = 0;
 		switch (req.operation) {
 		case BLKIF_OP_READ:
 			blkif->st_rd_req++;
-			ret = dispatch_rw_block_io(blkif, &req, pending_req); 
+			dispatch_rw_block_io(blkif, &req, pending_req);
 			break;
 		case BLKIF_OP_WRITE_BARRIER:
 			blkif->st_br_req++;
 			/* fall through */
 		case BLKIF_OP_WRITE:
 			blkif->st_wr_req++;
-			ret = dispatch_rw_block_io(blkif, &req, pending_req);
+			dispatch_rw_block_io(blkif, &req, pending_req);
 			break;
 		default:
 			/* A good sign something is wrong: sleep for a while to
@@ -386,17 +376,6 @@ handle_request:
 			free_req(pending_req);
 			break;
 		}
-        BUG_ON(ret != 0 && ret != -EAGAIN);
-        /* If we can't handle the request at the moment, save it, and break the
-         * loop */ 
-        if(ret == -EAGAIN)
-        {
-            memcpy(&blkif->suspended_req, &req, sizeof(req));
-            blkif->is_suspended_req = 1;
-            /* Return "no more work pending", restart will be handled 'out of
-             * band' */
-            return 0;
-        }
 
 		/* Yield point for this unbounded loop. */
 		cond_resched();
@@ -405,7 +384,7 @@ handle_request:
 	return more_to_do;
 }
 
-static int dispatch_rw_block_io(blkif_t *blkif,
+static void dispatch_rw_block_io(blkif_t *blkif,
 				 blkif_request_t *req,
 				 pending_req_t *pending_req)
 {
@@ -474,15 +453,13 @@ static int dispatch_rw_block_io(blkif_t
 	ret = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, map, nseg);
 	BUG_ON(ret);
 
-#define GENERAL_ERR   (1<<0)
-#define EAGAIN_ERR    (1<<1)
 	for (i = 0; i < nseg; i++) {
-		if (unlikely(map[i].status != 0)) {
+		if (unlikely(map[i].status == GNTST_eagain))
+			gnttab_check_GNTST_eagain_do_while(GNTTABOP_map_grant_ref, &map[i])
+		if (unlikely(map[i].status != GNTST_okay)) {
 			DPRINTK("invalid buffer -- could not remap it\n");
 			map[i].handle = BLKBACK_INVALID_HANDLE;
-			ret |= GENERAL_ERR;
-            if(map[i].status == GNTST_eagain)
-			    ret |= EAGAIN_ERR;
+			ret = 1;
 		} else {
 			blkback_pagemap_set(vaddr_pagenr(pending_req, i),
 					    pending_page(pending_req, i),
@@ -502,14 +479,6 @@ static int dispatch_rw_block_io(blkif_t
 			(req->seg[i].first_sect << 9);
 	}
 
-    /* If any of grant maps failed with GNTST_eagain, suspend and retry later */
-    if(ret & EAGAIN_ERR)
-    {
-        fast_flush_area(pending_req);
-        free_req(pending_req);
-        return -EAGAIN;
-    }
-
 	if (ret)
 		goto fail_flush;
 
@@ -575,7 +544,7 @@ static int dispatch_rw_block_io(blkif_t
 	else if (operation == WRITE || operation == WRITE_BARRIER)
 		blkif->st_wr_sect += preq.nr_sects;
 
-	return 0;
+	return;
 
  fail_flush:
 	fast_flush_area(pending_req);
@@ -583,7 +552,7 @@ static int dispatch_rw_block_io(blkif_t
 	make_response(blkif, req->id, req->operation, BLKIF_RSP_ERROR);
 	free_req(pending_req);
 	msleep(1); /* back off a bit */
-	return 0;
+	return;
 
  fail_put_bio:
 	__end_block_io_op(pending_req, -EINVAL);
@@ -591,7 +560,7 @@ static int dispatch_rw_block_io(blkif_t
 		bio_put(bio);
 	unplug_queue(blkif);
 	msleep(1); /* back off a bit */
-	return 0;
+	return;
 }
 
 
--- linux-2.6.18-xen.hg.orig/drivers/xen/blkback/common.h
+++ linux-2.6.18-xen.hg/drivers/xen/blkback/common.h
@@ -83,8 +83,6 @@ typedef struct blkif_st {
 	struct task_struct  *xenblkd;
 	unsigned int        waiting_reqs;
 	request_queue_t     *plug;
-    int                 is_suspended_req;
-    blkif_request_t     suspended_req;
 
 	/* statistics */
 	unsigned long       st_print;
--- linux-2.6.18-xen.hg.orig/drivers/xen/blkback/interface.c
+++ linux-2.6.18-xen.hg/drivers/xen/blkback/interface.c
@@ -59,25 +59,23 @@ blkif_t *blkif_alloc(domid_t domid)
 static int map_frontend_page(blkif_t *blkif, unsigned long shared_page)
 {
 	struct gnttab_map_grant_ref op;
+	int ret;
 
 	gnttab_set_map_op(&op, (unsigned long)blkif->blk_ring_area->addr,
 			  GNTMAP_host_map, shared_page, blkif->domid);
 
-    do {
-	    if (HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &op, 1))
-		    BUG();
-        msleep(100);
-    } while(op.status == GNTST_eagain);
+	gnttab_check_GNTST_eagain_do_while(GNTTABOP_map_grant_ref, &op);
 
-	if (op.status) {
-		DPRINTK(" Grant table operation failure !\n");
-		return op.status;
+	if (op.status == GNTST_okay) {
+		blkif->shmem_ref = shared_page;
+		blkif->shmem_handle = op.handle;
+		ret = 0;
+	} else {
+		DPRINTK(" Grant table operation failure %d!\n", (int)op.status);
+		ret = -EINVAL;
 	}
 
-	blkif->shmem_ref = shared_page;
-	blkif->shmem_handle = op.handle;
-
-	return 0;
+	return ret;
 }
 
 static void unmap_frontend_page(blkif_t *blkif)
--- linux-2.6.18-xen.hg.orig/drivers/xen/blktap/blktap.c
+++ linux-2.6.18-xen.hg/drivers/xen/blktap/blktap.c
@@ -1526,19 +1526,17 @@ static void dispatch_rw_block_io(blkif_t
 
 			uvaddr = MMAP_VADDR(info->user_vstart, usr_idx, i/2);
 
-			if (unlikely(map[i].status != 0)) {
-				WPRINTK("invalid kernel buffer -- "
-					"could not remap it\n");
-                if(map[i].status == GNTST_eagain)
-                    WPRINTK("grant GNTST_eagain: please use blktap2\n");
-				ret |= 1;
+			gnttab_check_GNTST_eagain_while(GNTTABOP_map_grant_ref, &map[i]);
+
+			if (unlikely(map[i].status != GNTST_okay)) {
+				WPRINTK("invalid kernel buffer -- could not remap it\n");
+				ret = 1;
 				map[i].handle = INVALID_GRANT_HANDLE;
 			}
 
-			if (unlikely(map[i+1].status != 0)) {
-				WPRINTK("invalid user buffer -- "
-					"could not remap it\n");
-				ret |= 1;
+			if (unlikely(map[i+1].status != GNTST_okay)) {
+				WPRINTK("invalid kernel buffer -- could not remap it\n");
+				ret = 1;
 				map[i+1].handle = INVALID_GRANT_HANDLE;
 			}
 
@@ -1565,12 +1563,11 @@ static void dispatch_rw_block_io(blkif_t
 
 			uvaddr = MMAP_VADDR(info->user_vstart, usr_idx, i);
 
-			if (unlikely(map[i].status != 0)) {
-				WPRINTK("invalid kernel buffer -- "
-					"could not remap it\n");
-                if(map[i].status == GNTST_eagain)
-                    WPRINTK("grant GNTST_eagain: please use blktap2\n");
-				ret |= 1;
+			gnttab_check_GNTST_eagain_while(GNTTABOP_map_grant_ref, &map[i]);
+
+			if (unlikely(map[i].status != GNTST_okay)) {
+				WPRINTK("invalid kernel buffer -- could not remap it\n");
+				ret = 1;
 				map[i].handle = INVALID_GRANT_HANDLE;
 			}
 
--- linux-2.6.18-xen.hg.orig/drivers/xen/blktap/interface.c
+++ linux-2.6.18-xen.hg/drivers/xen/blktap/interface.c
@@ -59,25 +59,23 @@ blkif_t *tap_alloc_blkif(domid_t domid)
 static int map_frontend_page(blkif_t *blkif, unsigned long shared_page)
 {
 	struct gnttab_map_grant_ref op;
+	int ret;
 
 	gnttab_set_map_op(&op, (unsigned long)blkif->blk_ring_area->addr,
 			  GNTMAP_host_map, shared_page, blkif->domid);
 
-    do {
-	    if (HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &op, 1))
-		    BUG();
-        msleep(10);
-    } while(op.status == GNTST_eagain);
+	gnttab_check_GNTST_eagain_do_while(GNTTABOP_map_grant_ref, &op);
 
-	if (op.status) {
-		DPRINTK(" Grant table operation failure !\n");
-		return op.status;
+	if (op.status == GNTST_okay) {
+		blkif->shmem_ref = shared_page;
+		blkif->shmem_handle = op.handle;
+		ret = 0;
+	} else {
+		DPRINTK("Grant table operation failure %d!\n", (int)op.status);
+		ret = -EINVAL;
 	}
 
-	blkif->shmem_ref = shared_page;
-	blkif->shmem_handle = op.handle;
-
-	return 0;
+	return ret;
 }
 
 static void unmap_frontend_page(blkif_t *blkif)
--- linux-2.6.18-xen.hg.orig/drivers/xen/blktap2/device.c
+++ linux-2.6.18-xen.hg/drivers/xen/blktap2/device.c
@@ -505,10 +505,10 @@ blktap_map_foreign(struct blktap *tap,
 
 		uvaddr = MMAP_VADDR(ring->user_vstart, usr_idx, i);
 
-		if (unlikely(table->grants[grant].status)) {
+		if (unlikely(table->grants[grant].status != GNTST_okay)) {
 			BTERR("invalid kernel buffer: could not remap it\n");
-            /* This should never happen: blkback should handle eagain first */
-            BUG_ON(table->grants[grant].status == GNTST_eagain);
+			/* This should never happen: blkback should handle eagain first */
+			BUG_ON(table->grants[grant].status == GNTST_eagain);
 			err |= 1;
 			table->grants[grant].handle = INVALID_GRANT_HANDLE;
 		}
@@ -517,19 +517,18 @@ blktap_map_foreign(struct blktap *tap,
 		foreign_mfn = table->grants[grant].dev_bus_addr >> PAGE_SHIFT;
 		grant++;
 
-		if (xen_feature(XENFEAT_auto_translated_physmap))
-			goto done;
-
-		if (unlikely(table->grants[grant].status)) {
-			BTERR("invalid user buffer: could not remap it\n");
-			err |= 1;
+		if (!xen_feature(XENFEAT_auto_translated_physmap)) {
+			if (unlikely(table->grants[grant].status != GNTST_okay)) {
+				/* This should never happen: blkback should handle eagain first */
+				WARN_ON(table->grants[grant].status == GNTST_eagain);
+				BTERR("invalid user buffer: could not remap it\n");
+				err |= 1;
+			}
 			table->grants[grant].handle = INVALID_GRANT_HANDLE;
+			request->handles[i].user = table->grants[grant].handle;
+			grant++;
 		}
 
-		request->handles[i].user = table->grants[grant].handle;
-		grant++;
-
-	done:
 		if (err)
 			continue;
 
@@ -602,11 +601,10 @@ blktap_map(struct blktap *tap,
 		set_page_private(tap_page, page_private(page));
 		SetPageBlkback(tap_page);
 
-		err = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref,
-						&map, 1);
-		BUG_ON(err);
-        /* We are not expecting the grant op to fail */
-        BUG_ON(map.status != GNTST_okay);
+		gnttab_check_GNTST_eagain_do_while(GNTTABOP_map_grant_ref, &map);
+
+		/* We are not expecting the grant op to fail */
+		BUG_ON(map.status != GNTST_okay);
 
 		err = vm_insert_page(ring->vma, uvaddr, tap_page);
 		if (err) {
--- linux-2.6.18-xen.hg.orig/drivers/xen/core/gnttab.c
+++ linux-2.6.18-xen.hg/drivers/xen/core/gnttab.c
@@ -487,7 +487,7 @@ static int gnttab_map(unsigned int start
 		return -ENOSYS;
 	}
 
-	BUG_ON(rc || setup.status);
+	BUG_ON(rc || setup.status != GNTST_okay);
 
 	if (shared == NULL)
 		shared = arch_gnttab_alloc_shared(frames);
@@ -571,7 +571,7 @@ int gnttab_copy_grant_page(grant_ref_t r
 	err = HYPERVISOR_grant_table_op(GNTTABOP_unmap_and_replace,
 					&unmap, 1);
 	BUG_ON(err);
-	BUG_ON(unmap.status);
+	BUG_ON(unmap.status != GNTST_okay);
 
 	write_sequnlock(&gnttab_dma_lock);
 
--- linux-2.6.18-xen.hg.orig/drivers/xen/gntdev/gntdev.c
+++ linux-2.6.18-xen.hg/drivers/xen/gntdev/gntdev.c
@@ -578,7 +578,7 @@ static int gntdev_mmap (struct file *fli
 	vma->vm_mm->context.has_foreign_mappings = 1;
 #endif
 
-    exit_ret = -ENOMEM;
+	exit_ret = -ENOMEM;
 	for (i = 0; i < size; ++i) {
 
 		flags = GNTMAP_host_map;
@@ -599,8 +599,8 @@ static int gntdev_mmap (struct file *fli
 		ret = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, 
 						&op, 1);
 		BUG_ON(ret);
-		if (op.status) {
-            if(op.status != GNTST_eagain)
+		if (op.status != GNTST_okay) {
+			if (op.status != GNTST_eagain)
 				printk(KERN_ERR "Error mapping the grant reference "
 				       "into the kernel (%d). domid = %d; ref = %d\n",
 				       op.status,
@@ -608,9 +608,9 @@ static int gntdev_mmap (struct file *fli
 				       .u.valid.domid,
 				       private_data->grants[slot_index+i]
 				       .u.valid.ref);
-            else 
-                /* Propagate eagain instead of trying to fix it up */
-                exit_ret = -EAGAIN;
+			else
+				/* Propagate eagain instead of trying to fix it up */
+				exit_ret = -EAGAIN;
 			goto undo_map_out;
 		}
 
@@ -679,7 +679,7 @@ static int gntdev_mmap (struct file *fli
 			ret = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref,
 							&op, 1);
 			BUG_ON(ret);
-			if (op.status) {
+			if (op.status != GNTST_okay) {
 				printk(KERN_ERR "Error mapping the grant "
 				       "reference into user space (%d). domid "
 				       "= %d; ref = %d\n", op.status,
@@ -687,9 +687,9 @@ static int gntdev_mmap (struct file *fli
 				       .valid.domid,
 				       private_data->grants[slot_index+i].u
 				       .valid.ref);
-                /* This should never happen after we've mapped into 
-                 * the kernel space. */
-                BUG_ON(op.status == GNTST_eagain);
+				/* This should never happen after we've mapped into
+				* the kernel space. */
+				BUG_ON(op.status == GNTST_eagain);
 				goto undo_map_out;
 			}
 			
@@ -713,7 +713,7 @@ static int gntdev_mmap (struct file *fli
 		}
 
 	}
-    exit_ret = 0;
+	exit_ret = 0;
 
 	up_write(&private_data->grants_sem);
 	return exit_ret;
@@ -785,7 +785,7 @@ static pte_t gntdev_clear_pte(struct vm_
 			ret = HYPERVISOR_grant_table_op(
 				GNTTABOP_unmap_grant_ref, &op, 1);
 			BUG_ON(ret);
-			if (op.status)
+			if (op.status != GNTST_okay)
 				printk("User unmap grant status = %d\n", 
 				       op.status);
 		} else {
@@ -802,7 +802,7 @@ static pte_t gntdev_clear_pte(struct vm_
 		ret = HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref, 
 						&op, 1);
 		BUG_ON(ret);
-		if (op.status)
+		if (op.status != GNTST_okay)
 			printk("Kernel unmap grant status = %d\n", op.status);
 
 
--- linux-2.6.18-xen.hg.orig/drivers/xen/netback/interface.c
+++ linux-2.6.18-xen.hg/drivers/xen/netback/interface.c
@@ -251,15 +251,11 @@ static int map_frontend_pages(
 
 	gnttab_set_map_op(&op, (unsigned long)netif->tx_comms_area->addr,
 			  GNTMAP_host_map, tx_ring_ref, netif->domid);
-    do {
-		if (HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &op, 1))
-			BUG();
-        msleep(10);
-    } while(op.status == GNTST_eagain);
-
-	if (op.status) { 
-		DPRINTK(" Gnttab failure mapping tx_ring_ref!\n");
-		return op.status;
+	gnttab_check_GNTST_eagain_do_while(GNTTABOP_map_grant_ref, &op);
+
+	if (op.status != GNTST_okay) {
+		DPRINTK(" Gnttab failure mapping tx_ring_ref %d!\n", (int)op.status);
+		return -EINVAL;
 	}
 
 	netif->tx_shmem_ref    = tx_ring_ref;
@@ -267,13 +263,9 @@ static int map_frontend_pages(
 
 	gnttab_set_map_op(&op, (unsigned long)netif->rx_comms_area->addr,
 			  GNTMAP_host_map, rx_ring_ref, netif->domid);
-    do {
-	    if (HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &op, 1))
-		    BUG();
-        msleep(10);
-    } while(op.status == GNTST_eagain);
+	gnttab_check_GNTST_eagain_do_while(GNTTABOP_map_grant_ref, &op);
 
-	if (op.status) {
+	if (op.status != GNTST_okay) {
 		struct gnttab_unmap_grant_ref unop;
 
 		gnttab_set_unmap_op(&unop,
@@ -281,8 +273,8 @@ static int map_frontend_pages(
 				    GNTMAP_host_map, netif->tx_shmem_handle);
 		VOID(HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref,
 					       &unop, 1));
-		DPRINTK(" Gnttab failure mapping rx_ring_ref!\n");
-		return op.status;
+		DPRINTK(" Gnttab failure mapping rx_ring_ref %d!\n", (int)op.status);
+		return -EINVAL;
 	}
 
 	netif->rx_shmem_ref    = rx_ring_ref;
--- linux-2.6.18-xen.hg.orig/drivers/xen/netback/netback.c
+++ linux-2.6.18-xen.hg/drivers/xen/netback/netback.c
@@ -494,8 +494,7 @@ static inline void netbk_free_pages(int
    used to set up the operations on the top of
    netrx_pending_operations, which have since been done.  Check that
    they didn't give any errors and advance over them. */
-static int netbk_check_gop(int nr_frags, domid_t domid,
-			   struct netrx_pending_operations *npo, int *eagain)
+static int netbk_check_gop(int nr_frags, domid_t domid, struct netrx_pending_operations *npo)
 {
 	multicall_entry_t *mcl;
 	gnttab_transfer_t *gop;
@@ -503,17 +502,15 @@ static int netbk_check_gop(int nr_frags,
 	int status = NETIF_RSP_OKAY;
 	int i;
 
-    *eagain = 0;
-
 	for (i = 0; i <= nr_frags; i++) {
 		if (npo->meta[npo->meta_cons + i].copy) {
 			copy_op = npo->copy + npo->copy_cons++;
-			if (copy_op->status != GNTST_okay) {
+			if (unlikely(copy_op->status == GNTST_eagain))
+				gnttab_check_GNTST_eagain_while(GNTTABOP_copy, copy_op);
+			if (unlikely(copy_op->status != GNTST_okay)) {
 				DPRINTK("Bad status %d from copy to DOM%d.\n",
 					copy_op->status, domid);
 				status = NETIF_RSP_ERROR;
-                if(copy_op->status == GNTST_eagain)
-                    *eagain = 1;
 			}
 		} else {
 			if (!xen_feature(XENFEAT_auto_translated_physmap)) {
@@ -524,7 +521,7 @@ static int netbk_check_gop(int nr_frags,
 
 			gop = npo->trans + npo->trans_cons++;
 			/* Check the reassignment error code. */
-			if (gop->status != 0) {
+			if (unlikely(gop->status != GNTST_okay)) {
 				DPRINTK("Bad status %d from grant transfer to DOM%u\n",
 					gop->status, domid);
 				/*
@@ -533,8 +530,6 @@ static int netbk_check_gop(int nr_frags,
 				 * a fatal error anyway.
 				 */
 				BUG_ON(gop->status == GNTST_bad_page);
-                if(gop->status == GNTST_eagain)
-                    *eagain = 1;
 				status = NETIF_RSP_ERROR;
 			}
 		}
@@ -576,7 +571,6 @@ static void net_rx_action(unsigned long
 	int nr_frags;
 	int count;
 	unsigned long offset;
-    int eagain;
 
 	/*
 	 * Putting hundreds of bytes on the stack is considered rude.
@@ -680,7 +674,7 @@ static void net_rx_action(unsigned long
 
 		netif = netdev_priv(skb->dev);
 
-		status = netbk_check_gop(nr_frags, netif->domid, &npo, &eagain);
+		status = netbk_check_gop(nr_frags, netif->domid, &npo);
 
 		/* We can't rely on skb_release_data to release the
 		   pages used by fragments for us, since it tries to
@@ -691,22 +685,14 @@ static void net_rx_action(unsigned long
 		/* (Freeing the fragments is safe since we copy
 		   non-linear skbs destined for flipping interfaces) */
 		if (!netif->copying_receiver) {
-            /* 
-             * Cannot handle failed grant transfers at the moment (because
-             * mmu_updates likely completed)
-             */
-            BUG_ON(eagain);
 			atomic_set(&(skb_shinfo(skb)->dataref), 1);
 			skb_shinfo(skb)->frag_list = NULL;
 			skb_shinfo(skb)->nr_frags = 0;
 			netbk_free_pages(nr_frags, meta + npo.meta_cons + 1);
 		}
 
-        if(!eagain)
-        {
-		    netif->stats.tx_bytes += skb->len;
-		    netif->stats.tx_packets++;
-        }
+		netif->stats.tx_bytes += skb->len;
+		netif->stats.tx_packets++;
 
 		id = meta[npo.meta_cons].id;
 		flags = nr_frags ? NETRXF_more_data : 0;
@@ -756,18 +742,8 @@ static void net_rx_action(unsigned long
 		    !netbk_queue_full(netif))
 			netif_wake_queue(netif->dev);
 
-        if(!eagain || netbk_queue_full(netif))
-        {
-		    netif_put(netif);
-		    dev_kfree_skb(skb);
-		    netif->stats.tx_dropped += !!eagain;
-        } 
-        else
-        {
-	        netif->rx_req_cons_peek += skb_shinfo(skb)->nr_frags + 1 +
-				   !!skb_shinfo(skb)->gso_size;
-            skb_queue_head(&rx_queue, skb);
-        }
+		netif_put(netif);
+		dev_kfree_skb(skb);
 
 		npo.meta_cons += nr_frags + 1;
 	}
@@ -1107,7 +1083,7 @@ static int netbk_tx_check_mop(struct sk_
 
 	/* Check status of header. */
 	err = mop->status;
-	if (unlikely(err)) {
+	if (unlikely(err != GNTST_okay)) {
 		txp = &pending_tx_info[pending_idx].req;
 		make_tx_response(netif, txp, NETIF_RSP_ERROR);
 		pending_ring[MASK_PEND_IDX(pending_prod++)] = pending_idx;
@@ -1128,12 +1104,12 @@ static int netbk_tx_check_mop(struct sk_
 
 		/* Check error status: if okay then remember grant handle. */
 		newerr = (++mop)->status;
-		if (likely(!newerr)) {
+		if (likely(newerr == GNTST_okay)) {
 			set_phys_to_machine(idx_to_pfn(pending_idx),
 				FOREIGN_FRAME(mop->dev_bus_addr>>PAGE_SHIFT));
 			grant_tx_handle[pending_idx] = mop->handle;
 			/* Had a previous error? Invalidate this fragment. */
-			if (unlikely(err))
+			if (unlikely(err != GNTST_okay))
 				netif_idx_release(pending_idx);
 			continue;
 		}
@@ -1145,7 +1121,7 @@ static int netbk_tx_check_mop(struct sk_
 		netif_put(netif);
 
 		/* Not the first error? Preceding frags already invalidated. */
-		if (err)
+		if (err != GNTST_okay)
 			continue;
 
 		/* First error: invalidate header and preceding fragments. */
--- linux-2.6.18-xen.hg.orig/drivers/xen/scsiback/interface.c
+++ linux-2.6.18-xen.hg/drivers/xen/scsiback/interface.c
@@ -64,27 +64,23 @@ static int map_frontend_page( struct vsc
 				unsigned long ring_ref)
 {
 	struct gnttab_map_grant_ref op;
-	int err;
+	int ret;
 
 	gnttab_set_map_op(&op, (unsigned long)info->ring_area->addr,
 				GNTMAP_host_map, ring_ref,
 				info->domid);
+	gnttab_check_GNTST_eagain_do_while(GNTTABOP_map_grant_ref, &op);
 
-    do {
-	    err = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &op, 1);
-	    BUG_ON(err);
-        msleep(10);
-    } while(op.status == GNTST_eagain);
-
-	if (op.status) {
-		printk(KERN_ERR "scsiback: Grant table operation failure !\n");
-		return op.status;
+	if (op.status != GNTST_okay) {
+		printk(KERN_ERR "scsiback: Grant table operation failure %d!\n", (int)op.status);
+		ret = -EINVAL;
+	} else {
+		info->shmem_ref    = ring_ref;
+		info->shmem_handle = op.handle;
+		ret = 0;
 	}
 
-	info->shmem_ref    = ring_ref;
-	info->shmem_handle = op.handle;
-
-	return (GNTST_okay);
+	return ret;
 }
 
 static void unmap_frontend_page(struct vscsibk_info *info)
--- linux-2.6.18-xen.hg.orig/drivers/xen/scsiback/scsiback.c
+++ linux-2.6.18-xen.hg/drivers/xen/scsiback/scsiback.c
@@ -279,22 +279,14 @@ static int scsiback_gnttab_data_map(vscs
 
 		err = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, map, nr_segments);
 		BUG_ON(err);
-        /* Retry maps with GNTST_eagain */
-        for(i=0; i < nr_segments; i++) {
-            while(unlikely(map[i].status == GNTST_eagain))
-            {
-                msleep(10);
-		        err = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, 
-                                                &map[i], 
-                                                1);
-		        BUG_ON(err);
-            }
-        }
 
 		for (i = 0; i < nr_segments; i++) {
 			struct page *pg;
 
-			if (unlikely(map[i].status != 0)) {
+			/* Retry maps with GNTST_eagain */
+			if (unlikely(map[i].status == GNTST_eagain))
+				gnttab_check_GNTST_eagain_while(GNTTABOP_map_grant_ref, &map[i]);
+			if (unlikely(map[i].status != GNTST_okay)) {
 				printk(KERN_ERR "scsiback: invalid buffer -- could not remap it\n");
 				map[i].handle = SCSIBACK_INVALID_HANDLE;
 				err |= 1;
--- linux-2.6.18-xen.hg.orig/drivers/xen/sfc_netutil/accel_util.c
+++ linux-2.6.18-xen.hg/drivers/xen/sfc_netutil/accel_util.c
@@ -71,24 +71,27 @@ static int net_accel_map_grant(struct xe
 			       u64 *dev_bus_addr, unsigned flags)
 {
 	struct gnttab_map_grant_ref op;
+	int ret;
 	
 	gnttab_set_map_op(&op, (unsigned long)vaddr, flags,
 			  gnt_ref, dev->otherend_id);
 
-	BUG_ON(HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &op, 1));
+	gnttab_check_GNTST_eagain_do_while(GNTTABOP_map_grant_ref, &op);
 
 	if (op.status != GNTST_okay) {
 		xenbus_dev_error
 			(dev, op.status,
 			 "failed mapping in shared page %d from domain %d\n",
 			 gnt_ref, dev->otherend_id);
+		ret = -EINVAL;
 	} else {
 		*handle = op.handle;
 		if (dev_bus_addr)
 			*dev_bus_addr = op.dev_bus_addr;
+		ret = 0;
 	}
 
-	return op.status;
+	return ret;
 }
 
 
@@ -112,7 +115,7 @@ static int net_accel_unmap_grant(struct
 				 "failed unmapping page at handle %d error %d\n",
 				 handle, op.status);
 
-	return op.status;
+	return op.status == GNTST_okay ? 0 : -EINVAL;
 }
 
 
@@ -144,7 +147,7 @@ struct net_accel_valloc_grant_mapping {
 /* Map a series of grants into a contiguous virtual area */
 static void *net_accel_map_grants_valloc(struct xenbus_device *dev, 
 					 unsigned *grants, int npages, 
-					 unsigned flags, void **priv, int *errno)
+					 unsigned flags, void **priv)
 {
 	struct net_accel_valloc_grant_mapping *map;
 	struct vm_struct *vm;
@@ -172,16 +175,12 @@ static void *net_accel_map_grants_valloc
 
 	/* Do the actual mapping */
 	addr = vm->addr;
-    if(errno != NULL) *errno = 0;
+
 	for (i = 0; i < npages; i++) {
 		rc = net_accel_map_grant(dev, grants[i], map->grant_handles + i, 
 					 addr, NULL, flags);
-		if (rc != 0)
-        {
-            if(errno != NULL) 
-                *errno = (rc == GNTST_eagain ? -EAGAIN : -EINVAL);
+		if (rc < 0)
 			goto undo;
-        }
 		addr = (void*)((unsigned long)addr + PAGE_SIZE);
 	}
 
@@ -230,16 +229,7 @@ void *net_accel_map_grants_contig(struct
 				unsigned *grants, int npages, 
 				void **priv)
 {
-    int errno;
-    void *ret;
-
-    do {
-	    ret = net_accel_map_grants_valloc(dev, grants, npages,
-					   GNTMAP_host_map, priv, &errno);
-        if(errno) msleep(10);
-    } while(errno == -EAGAIN);
-
-    return ret;
+    return net_accel_map_grants_valloc(dev, grants, npages, GNTMAP_host_map, priv);
 }
 EXPORT_SYMBOL(net_accel_map_grants_contig);
 
@@ -255,16 +245,7 @@ EXPORT_SYMBOL(net_accel_unmap_grants_con
 void *net_accel_map_iomem_page(struct xenbus_device *dev, int gnt_ref,
 			     void **priv)
 {
-    int errno;
-    void *ret;
-
-	do {
-        ret = net_accel_map_grants_valloc(dev, &gnt_ref, 1, 
-					   GNTMAP_host_map, priv, &errno);
-        if(errno) msleep(10);
-    } while(errno == -EAGAIN);
-
-    return ret;
+	return net_accel_map_grants_valloc(dev, &gnt_ref, 1, GNTMAP_host_map, priv);
 }
 EXPORT_SYMBOL(net_accel_map_iomem_page);
 
--- linux-2.6.18-xen.hg.orig/drivers/xen/tpmback/interface.c
+++ linux-2.6.18-xen.hg/drivers/xen/tpmback/interface.c
@@ -81,25 +81,23 @@ tpmif_t *tpmif_find(domid_t domid, struc
 static int map_frontend_page(tpmif_t *tpmif, unsigned long shared_page)
 {
 	struct gnttab_map_grant_ref op;
+	int ret;
 
 	gnttab_set_map_op(&op, (unsigned long)tpmif->tx_area->addr,
 			  GNTMAP_host_map, shared_page, tpmif->domid);
 
-    do {
-	    if (HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &op, 1))
-		    BUG();
-        msleep(10);
-    } while(op.status == GNTST_eagain);
+	gnttab_check_GNTST_eagain_do_while(GNTTABOP_map_grant_ref, &op);
 
-	if (op.status) {
-		DPRINTK(" Grant table operation failure !\n");
-		return op.status;
+	if (op.status != GNTST_okay) {
+		DPRINTK(" Grant table operation failure %d!\n", (int)op.status);
+		ret = -EINVAL;
+	} else {
+		tpmif->shmem_ref = shared_page;
+		tpmif->shmem_handle = op.handle;
+		ret = 0;
 	}
 
-	tpmif->shmem_ref = shared_page;
-	tpmif->shmem_handle = op.handle;
-
-	return 0;
+	return ret;
 }
 
 static void unmap_frontend_page(tpmif_t *tpmif)
--- linux-2.6.18-xen.hg.orig/drivers/xen/tpmback/tpmback.c
+++ linux-2.6.18-xen.hg/drivers/xen/tpmback/tpmback.c
@@ -257,20 +257,15 @@ int _packet_write(struct packet *pak,
 		gnttab_set_map_op(&map_op, idx_to_kaddr(tpmif, i),
 				  GNTMAP_host_map, tx->ref, tpmif->domid);
 
-        do {
-		    if (unlikely(HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref,
-						       &map_op, 1)))
-			    BUG();
-            if(map_op.status) msleep(10);
-		} while(map_op.status == GNTST_eagain);
+		gnttab_check_GNTST_eagain_do_while(GNTTABOP_map_grant_ref, &map_op);
 
-		handle = map_op.handle;
-
-		if (map_op.status) {
+		if (map_op.status != GNTST_okay) {
 			DPRINTK(" Grant table operation failure !\n");
 			return 0;
 		}
 
+		handle = map_op.handle;
+
 		tocopy = min_t(size_t, size - offset, PAGE_SIZE);
 
 		if (copy_from_buffer((void *)(idx_to_kaddr(tpmif, i) |
@@ -397,14 +392,9 @@ static int packet_read_shmem(struct pack
 		gnttab_set_map_op(&map_op, idx_to_kaddr(tpmif, i),
 				  GNTMAP_host_map, tx->ref, tpmif->domid);
 
-        do {
-		    if (unlikely(HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref,
-						       &map_op, 1)))
-			    BUG();
-            if(map_op.status) msleep(10);
-		} while(map_op.status == GNTST_eagain);
+		gnttab_check_GNTST_eagain_do_while(GNTTABOP_map_grant_ref, &map_op);
 
-		if (map_op.status) {
+		if (map_op.status != GNTST_okay) {
 			DPRINTK(" Grant table operation failure !\n");
 			return -EFAULT;
 		}
--- linux-2.6.18-xen.hg.orig/drivers/xen/usbback/interface.c
+++ linux-2.6.18-xen.hg/drivers/xen/usbback/interface.c
@@ -110,16 +110,11 @@ static int map_frontend_pages(usbif_t *u
 	gnttab_set_map_op(&op, (unsigned long)usbif->urb_ring_area->addr,
 			  GNTMAP_host_map, urb_ring_ref, usbif->domid);
 
+	gnttab_check_GNTST_eagain_do_while(GNTTABOP_map_grant_ref, &op);
 
-    do {
-	    if (HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &op, 1))
-		    BUG();
-        msleep(10);
-    } while (op.status == GNTST_eagain);
-
-	if (op.status) {
-		printk(KERN_ERR "grant table failure mapping urb_ring_ref\n");
-		return op.status;
+	if (op.status != GNTST_okay) {
+		printk(KERN_ERR "grant table failure mapping urb_ring_ref %d\n", (int)op.status);
+		return -EINVAL;
 	}
 
 	usbif->urb_shmem_ref = urb_ring_ref;
@@ -128,21 +123,17 @@ static int map_frontend_pages(usbif_t *u
 	gnttab_set_map_op(&op, (unsigned long)usbif->conn_ring_area->addr,
 			  GNTMAP_host_map, conn_ring_ref, usbif->domid);
 
-    do {
-	    if (HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &op, 1))
-		    BUG();
-        msleep(10);
-    } while (op.status == GNTST_eagain);
+	gnttab_check_GNTST_eagain_do_while(GNTTABOP_map_grant_ref, &op);
 
-	if (op.status) {
+	if (op.status != GNTST_okay) {
 		struct gnttab_unmap_grant_ref unop;
 		gnttab_set_unmap_op(&unop,
 				(unsigned long) usbif->urb_ring_area->addr,
 				GNTMAP_host_map, usbif->urb_shmem_handle);
 		VOID(HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref, &unop,
 				1));
-		printk(KERN_ERR "grant table failure mapping conn_ring_ref\n");
-		return op.status;
+		printk(KERN_ERR "grant table failure mapping conn_ring_ref %d\n", (int)op.status);
+		return -EINVAL;
 	}
 
 	usbif->conn_shmem_ref = conn_ring_ref;
--- linux-2.6.18-xen.hg.orig/drivers/xen/usbback/usbback.c
+++ linux-2.6.18-xen.hg/drivers/xen/usbback/usbback.c
@@ -392,19 +392,13 @@ static int usbbk_gnttab_map(usbif_t *usb
 		ret = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref,
 					map, nr_segs);
 		BUG_ON(ret);
-        /* Make sure than none of the map ops failed with GNTST_eagain */
-        for( i = 0; i < nr_segs; i++) {
-            while(map[i].status == GNTST_eagain) {
-                msleep(10);
-		        ret = HYPERVISOR_grant_table_op(
-                                GNTTABOP_map_grant_ref,
-				                &map[i], 1);
-		        BUG_ON(ret);
-            }
-        }
 
 		for (i = 0; i < nr_segs; i++) {
-			if (unlikely(map[i].status != 0)) {
+			/* Make sure than none of the map ops failed with GNTST_eagain */
+			if (unlikely(map[i].status == GNTST_eagain))
+				gnttab_check_GNTST_eagain_while(GNTTABOP_map_grant_ref, &map[i]);
+
+			if (unlikely(map[i].status != GNTST_okay)) {
 				printk(KERN_ERR "usbback: invalid buffer -- could not remap it\n");
 				map[i].handle = USBBACK_INVALID_HANDLE;
 				ret |= 1;
--- linux-2.6.18-xen.hg.orig/drivers/xen/xenbus/xenbus_backend_client.c
+++ linux-2.6.18-xen.hg/drivers/xen/xenbus/xenbus_backend_client.c
@@ -49,11 +49,7 @@ struct vm_struct *xenbus_map_ring_valloc
 	gnttab_set_map_op(&op, (unsigned long)area->addr, GNTMAP_host_map,
 			  gnt_ref, dev->otherend_id);
 	
-    do {
-	    if (HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &op, 1))
-		    BUG();
-        msleep(10);
-    } while(op.status == GNTST_eagain);
+	gnttab_check_GNTST_eagain_do_while(GNTTABOP_map_grant_ref, &op);
 
 	if (op.status != GNTST_okay) {
 		free_vm_area(area);
@@ -61,7 +57,7 @@ struct vm_struct *xenbus_map_ring_valloc
 				 "mapping in shared page %d from domain %d",
 				 gnt_ref, dev->otherend_id);
 		BUG_ON(!IS_ERR(ERR_PTR(op.status)));
-		return ERR_PTR(op.status);
+		return ERR_PTR(-EINVAL);
 	}
 
 	/* Stuff the handle in an unused field */
@@ -76,23 +72,24 @@ int xenbus_map_ring(struct xenbus_device
 		   grant_handle_t *handle, void *vaddr)
 {
 	struct gnttab_map_grant_ref op;
+	int ret;
 	
 	gnttab_set_map_op(&op, (unsigned long)vaddr, GNTMAP_host_map,
 			  gnt_ref, dev->otherend_id);
-    do {
-	    if (HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &op, 1))
-		    BUG();
-        msleep(10);
-    } while(op.status == GNTST_eagain);
+
+	gnttab_check_GNTST_eagain_do_while(GNTTABOP_map_grant_ref, &op);
 
 	if (op.status != GNTST_okay) {
 		xenbus_dev_fatal(dev, op.status,
 				 "mapping in shared page %d from domain %d",
 				 gnt_ref, dev->otherend_id);
-	} else
+		ret = -EINVAL;
+	} else {
 		*handle = op.handle;
+		ret = 0;
+	}
 
-	return op.status;
+	return ret;
 }
 EXPORT_SYMBOL_GPL(xenbus_map_ring);
 
@@ -115,7 +112,7 @@ int xenbus_unmap_ring_vfree(struct xenbu
 				 "unmapping page at handle %d error %d",
 				 (int16_t)area->phys_addr, op.status);
 
-	return op.status;
+	return op.status == GNTST_okay ? 0 : -EINVAL;
 }
 EXPORT_SYMBOL_GPL(xenbus_unmap_ring_vfree);
 
@@ -135,7 +132,7 @@ int xenbus_unmap_ring(struct xenbus_devi
 				 "unmapping page at handle %d error %d",
 				 handle, op.status);
 
-	return op.status;
+	return op.status == GNTST_okay ? 0 : -EINVAL;
 }
 EXPORT_SYMBOL_GPL(xenbus_unmap_ring);
 
--- linux-2.6.18-xen.hg.orig/include/xen/gnttab.h
+++ linux-2.6.18-xen.hg/include/xen/gnttab.h
@@ -40,6 +40,7 @@
 #include <asm/hypervisor.h>
 #include <asm/maddr.h> /* maddr_t */
 #include <linux/mm.h>
+#include <linux/delay.h>
 #include <xen/interface/grant_table.h>
 #include <xen/features.h>
 
@@ -161,4 +162,41 @@ gnttab_set_replace_op(struct gnttab_unma
 	unmap->handle = handle;
 }
 
+#define gnttab_check_GNTST_eagain_while(__HCop, __HCarg_p)			\
+{										\
+	u8 __hc_delay = 1;							\
+	int __ret;								\
+	while (unlikely((__HCarg_p)->status == GNTST_eagain && __hc_delay)) {	\
+		msleep(__hc_delay++);						\
+		__ret = HYPERVISOR_grant_table_op(__HCop, (__HCarg_p), 1);	\
+		BUG_ON(__ret);							\
+	}									\
+	if (__hc_delay == 0) {							\
+		printk(KERN_ERR "%s: %s gnt busy\n", __func__, current->comm);	\
+		(__HCarg_p)->status = GNTST_bad_page;				\
+	}									\
+	if ((__HCarg_p)->status != GNTST_okay)					\
+		printk(KERN_ERR "%s: %s gnt status %x\n", 			\
+			__func__, current->comm, (__HCarg_p)->status);		\
+}
+
+#define gnttab_check_GNTST_eagain_do_while(__HCop, __HCarg_p)			\
+{										\
+	u8 __hc_delay = 1;							\
+	int __ret;								\
+	do {									\
+		__ret = HYPERVISOR_grant_table_op(__HCop, (__HCarg_p), 1);	\
+		BUG_ON(__ret);							\
+		if ((__HCarg_p)->status == GNTST_eagain)			\
+			msleep(__hc_delay++);					\
+	} while ((__HCarg_p)->status == GNTST_eagain && __hc_delay);		\
+	if (__hc_delay == 0) {							\
+		printk(KERN_ERR "%s: %s gnt busy\n", __func__, current->comm);	\
+		(__HCarg_p)->status = GNTST_bad_page;				\
+	}									\
+	if ((__HCarg_p)->status != GNTST_okay)					\
+		printk(KERN_ERR "%s: %s gnt status %x\n", 			\
+			__func__, current->comm, (__HCarg_p)->status);		\
+}
+
 #endif /* __ASM_GNTTAB_H__ */