vhost: extend memory regions allocation to vmalloc

with large number of memory regions we could end up with
high order allocations and kmalloc could fail if
host is under memory pressure.
Considering that memory regions array is used on hot path
try harder to allocate using kmalloc and if it fails resort
to vmalloc.
It's still better than just failing vhost_set_memory() and
causing guest crash due to it when a new memory hotplugged
to guest.

I'll still look at QEMU side solution to reduce amount of
memory regions it feeds to vhost to make things even better,
but it doesn't hurt for kernel to behave smarter and don't
crash older QEMU's which could use large amount of memory
regions.
Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/vhost/vhost.c

@@ -22,6 +22,7 @@
 #include <linux/file.h>
 #include <linux/highmem.h>
 #include <linux/slab.h>
+#include <linux/vmalloc.h>
 #include <linux/kthread.h>
 #include <linux/cgroup.h>
 #include <linux/module.h>
@@ -544,7 +545,7 @@ void vhost_dev_cleanup(struct vhost_dev *dev, bool locked)
 		fput(dev->log_file);
 	dev->log_file = NULL;
 	/* No one will access memory at this point */
-	kfree(dev->memory);
+	kvfree(dev->memory);
 	dev->memory = NULL;
 	WARN_ON(!list_empty(&dev->work_list));
 	if (dev->worker) {
@@ -674,6 +675,18 @@ static int vhost_memory_reg_sort_cmp(const void *p1, const void *p2)
 	return 0;
 }
 
+static void *vhost_kvzalloc(unsigned long size)
+{
+	void *n = kzalloc(size, GFP_KERNEL | __GFP_NOWARN | __GFP_REPEAT);
+
+	if (!n) {
+		n = vzalloc(size);
+		if (!n)
+			return ERR_PTR(-ENOMEM);
+	}
+	return n;
+}
+
 static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m)
 {
 	struct vhost_memory mem, *newmem, *oldmem;
@@ -686,7 +699,7 @@ static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m)
 		return -EOPNOTSUPP;
 	if (mem.nregions > VHOST_MEMORY_MAX_NREGIONS)
 		return -E2BIG;
-	newmem = kmalloc(size + mem.nregions * sizeof *m->regions, GFP_KERNEL);
+	newmem = vhost_kvzalloc(size + mem.nregions * sizeof(*m->regions));
 	if (!newmem)
 		return -ENOMEM;
 
@@ -700,7 +713,7 @@ static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m)
 		vhost_memory_reg_sort_cmp, NULL);
 
 	if (!memory_access_ok(d, newmem, 0)) {
-		kfree(newmem);
+		kvfree(newmem);
 		return -EFAULT;
 	}
 	oldmem = d->memory;
@@ -712,7 +725,7 @@ static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m)
 		d->vqs[i]->memory = newmem;
 		mutex_unlock(&d->vqs[i]->mutex);
 	}
-	kfree(oldmem);
+	kvfree(oldmem);
 	return 0;
 }