xenbus: Support HVM backends

Add HVM implementations of xenbus_(map,unmap)_ring_v(alloc,free) so
that ring mappings can be done without using GNTMAP_contains_pte which
is not supported on HVM.  This also removes the need to use vmlist_lock
on PV by tracking the allocated xenbus rings.
Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
[v1: Fix compile error when XENBUS_FRONTEND is defined as module]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

drivers/xen/xenbus/xenbus_client.c

@@ -32,15 +32,39 @@
 
 #include <linux/slab.h>
 #include <linux/types.h>
+#include <linux/spinlock.h>
 #include <linux/vmalloc.h>
 #include <linux/export.h>
 #include <asm/xen/hypervisor.h>
 #include <asm/xen/page.h>
 #include <xen/interface/xen.h>
 #include <xen/interface/event_channel.h>
+#include <xen/balloon.h>
 #include <xen/events.h>
 #include <xen/grant_table.h>
 #include <xen/xenbus.h>
+#include <xen/xen.h>
+
+#include "xenbus_probe.h"
+
+struct xenbus_map_node {
+	struct list_head next;
+	union {
+		struct vm_struct *area; /* PV */
+		struct page *page;     /* HVM */
+	};
+	grant_handle_t handle;
+};
+
+static DEFINE_SPINLOCK(xenbus_valloc_lock);
+static LIST_HEAD(xenbus_valloc_pages);
+
+struct xenbus_ring_ops {
+	int (*map)(struct xenbus_device *dev, int gnt, void **vaddr);
+	int (*unmap)(struct xenbus_device *dev, void *vaddr);
+};
+
+static const struct xenbus_ring_ops *ring_ops __read_mostly;
 
 const char *xenbus_strstate(enum xenbus_state state)
 {
@@ -435,20 +459,34 @@ EXPORT_SYMBOL_GPL(xenbus_free_evtchn);
  * XenbusStateClosing and the error message will be saved in XenStore.
  */
 int xenbus_map_ring_valloc(struct xenbus_device *dev, int gnt_ref, void **vaddr)
+{
+	return ring_ops->map(dev, gnt_ref, vaddr);
+}
+EXPORT_SYMBOL_GPL(xenbus_map_ring_valloc);
+
+static int xenbus_map_ring_valloc_pv(struct xenbus_device *dev,
+				     int gnt_ref, void **vaddr)
 {
 	struct gnttab_map_grant_ref op = {
 		.flags = GNTMAP_host_map | GNTMAP_contains_pte,
 		.ref   = gnt_ref,
 		.dom   = dev->otherend_id,
 	};
+	struct xenbus_map_node *node;
 	struct vm_struct *area;
 	pte_t *pte;
 
 	*vaddr = NULL;
 
+	node = kzalloc(sizeof(*node), GFP_KERNEL);
+	if (!node)
+		return -ENOMEM;
+
 	area = alloc_vm_area(PAGE_SIZE, &pte);
-	if (!area)
+	if (!area) {
+		kfree(node);
 		return -ENOMEM;
+	}
 
 	op.host_addr = arbitrary_virt_to_machine(pte).maddr;
 
@@ -457,19 +495,59 @@ int xenbus_map_ring_valloc(struct xenbus_device *dev, int gnt_ref, void **vaddr)
 
 	if (op.status != GNTST_okay) {
 		free_vm_area(area);
+		kfree(node);
 		xenbus_dev_fatal(dev, op.status,
 				 "mapping in shared page %d from domain %d",
 				 gnt_ref, dev->otherend_id);
 		return op.status;
 	}
 
-	/* Stuff the handle in an unused field */
-	area->phys_addr = (unsigned long)op.handle;
+	node->handle = op.handle;
+	node->area = area;
+
+	spin_lock(&xenbus_valloc_lock);
+	list_add(&node->next, &xenbus_valloc_pages);
+	spin_unlock(&xenbus_valloc_lock);
 
 	*vaddr = area->addr;
 	return 0;
 }
-EXPORT_SYMBOL_GPL(xenbus_map_ring_valloc);
+
+static int xenbus_map_ring_valloc_hvm(struct xenbus_device *dev,
+				      int gnt_ref, void **vaddr)
+{
+	struct xenbus_map_node *node;
+	int err;
+	void *addr;
+
+	*vaddr = NULL;
+
+	node = kzalloc(sizeof(*node), GFP_KERNEL);
+	if (!node)
+		return -ENOMEM;
+
+	err = alloc_xenballooned_pages(1, &node->page, false /* lowmem */);
+	if (err)
+		goto out_err;
+
+	addr = pfn_to_kaddr(page_to_pfn(node->page));
+
+	err = xenbus_map_ring(dev, gnt_ref, &node->handle, addr);
+	if (err)
+		goto out_err;
+
+	spin_lock(&xenbus_valloc_lock);
+	list_add(&node->next, &xenbus_valloc_pages);
+	spin_unlock(&xenbus_valloc_lock);
+
+	*vaddr = addr;
+	return 0;
+
+ out_err:
+	free_xenballooned_pages(1, &node->page);
+	kfree(node);
+	return err;
+}
 
 
 /**
@@ -525,32 +603,36 @@ EXPORT_SYMBOL_GPL(xenbus_map_ring);
  */
 int xenbus_unmap_ring_vfree(struct xenbus_device *dev, void *vaddr)
 {
-	struct vm_struct *area;
+	return ring_ops->unmap(dev, vaddr);
+}
+EXPORT_SYMBOL_GPL(xenbus_unmap_ring_vfree);
+
+static int xenbus_unmap_ring_vfree_pv(struct xenbus_device *dev, void *vaddr)
+{
+	struct xenbus_map_node *node;
 	struct gnttab_unmap_grant_ref op = {
 		.host_addr = (unsigned long)vaddr,
 	};
 	unsigned int level;
 
-	/* It'd be nice if linux/vmalloc.h provided a find_vm_area(void *addr)
-	 * method so that we don't have to muck with vmalloc internals here.
-	 * We could force the user to hang on to their struct vm_struct from
-	 * xenbus_map_ring_valloc, but these 6 lines considerably simplify
-	 * this API.
-	 */
-	read_lock(&vmlist_lock);
-	for (area = vmlist; area != NULL; area = area->next) {
-		if (area->addr == vaddr)
-			break;
+	spin_lock(&xenbus_valloc_lock);
+	list_for_each_entry(node, &xenbus_valloc_pages, next) {
+		if (node->area->addr == vaddr) {
+			list_del(&node->next);
+			goto found;
+		}
 	}
-	read_unlock(&vmlist_lock);
+	node = NULL;
+ found:
+	spin_unlock(&xenbus_valloc_lock);
 
-	if (!area) {
+	if (!node) {
 		xenbus_dev_error(dev, -ENOENT,
 				 "can't find mapped virtual address %p", vaddr);
 		return GNTST_bad_virt_addr;
 	}
 
-	op.handle = (grant_handle_t)area->phys_addr;
+	op.handle = node->handle;
 	op.host_addr = arbitrary_virt_to_machine(
 		lookup_address((unsigned long)vaddr, &level)).maddr;
 
@@ -558,16 +640,50 @@ int xenbus_unmap_ring_vfree(struct xenbus_device *dev, void *vaddr)
 		BUG();
 
 	if (op.status == GNTST_okay)
-		free_vm_area(area);
+		free_vm_area(node->area);
 	else
 		xenbus_dev_error(dev, op.status,
 				 "unmapping page at handle %d error %d",
-				 (int16_t)area->phys_addr, op.status);
+				 node->handle, op.status);
 
+	kfree(node);
 	return op.status;
 }
-EXPORT_SYMBOL_GPL(xenbus_unmap_ring_vfree);
 
+static int xenbus_unmap_ring_vfree_hvm(struct xenbus_device *dev, void *vaddr)
+{
+	int rv;
+	struct xenbus_map_node *node;
+	void *addr;
+
+	spin_lock(&xenbus_valloc_lock);
+	list_for_each_entry(node, &xenbus_valloc_pages, next) {
+		addr = pfn_to_kaddr(page_to_pfn(node->page));
+		if (addr == vaddr) {
+			list_del(&node->next);
+			goto found;
+		}
+	}
+	node = NULL;
+ found:
+	spin_unlock(&xenbus_valloc_lock);
+
+	if (!node) {
+		xenbus_dev_error(dev, -ENOENT,
+				 "can't find mapped virtual address %p", vaddr);
+		return GNTST_bad_virt_addr;
+	}
+
+	rv = xenbus_unmap_ring(dev, node->handle, addr);
+
+	if (!rv)
+		free_xenballooned_pages(1, &node->page);
+	else
+		WARN(1, "Leaking %p\n", vaddr);
+
+	kfree(node);
+	return rv;
+}
 
 /**
  * xenbus_unmap_ring
@@ -617,3 +733,21 @@ enum xenbus_state xenbus_read_driver_state(const char *path)
 	return result;
 }
 EXPORT_SYMBOL_GPL(xenbus_read_driver_state);
+
+static const struct xenbus_ring_ops ring_ops_pv = {
+	.map = xenbus_map_ring_valloc_pv,
+	.unmap = xenbus_unmap_ring_vfree_pv,
+};
+
+static const struct xenbus_ring_ops ring_ops_hvm = {
+	.map = xenbus_map_ring_valloc_hvm,
+	.unmap = xenbus_unmap_ring_vfree_hvm,
+};
+
+void __init xenbus_ring_ops_init(void)
+{
+	if (xen_pv_domain())
+		ring_ops = &ring_ops_pv;
+	else
+		ring_ops = &ring_ops_hvm;
+}

drivers/xen/xenbus/xenbus_probe.c

@@ -730,6 +730,8 @@ static int __init xenbus_init(void)
 	if (!xen_domain())
 		return -ENODEV;
 
+	xenbus_ring_ops_init();
+
 	if (xen_hvm_domain()) {
 		uint64_t v = 0;
 		err = hvm_get_parameter(HVM_PARAM_STORE_EVTCHN, &v);

drivers/xen/xenbus/xenbus_probe.h

@@ -76,4 +76,6 @@ extern void xenbus_otherend_changed(struct xenbus_watch *watch,
 extern int xenbus_read_otherend_details(struct xenbus_device *xendev,
 					char *id_node, char *path_node);
 
+void xenbus_ring_ops_init(void);
+
 #endif