Allow xen_create_contiguous_region() to fail gracefully if it

cannot allocate a contiguous multi-page extent of memory. This
should avoid unnecessary crashes in the xen-specific skbuff
cache constructor.

Signed-off-by: Keir Fraser <keir@xensource.com>

linux-2.6-xen-sparse/arch/xen/i386/kernel/pci-dma.c

@@ -152,8 +152,11 @@ void *dma_alloc_coherent(struct device *dev, size_t size,
 	ret = (void *)vstart;
 
 	if (ret != NULL) {
-		xen_create_contiguous_region(vstart, order);
-
+		/* NB. Hardcode 31 address bits for now: aacraid limitation. */
+		if (xen_create_contiguous_region(vstart, order, 31) != 0) {
+			free_pages(vstart, order);
+			return NULL;
+		}
 		memset(ret, 0, size);
 		*dma_handle = virt_to_bus(ret);
 	}

linux-2.6-xen-sparse/arch/xen/i386/kernel/swiotlb.c

@@ -117,6 +117,7 @@ void
 swiotlb_init_with_default_size (size_t default_size)
 {
 	unsigned long i, bytes;
+	int rc;
 
 	if (!iotlb_nslabs) {
 		iotlb_nslabs = (default_size >> IO_TLB_SHIFT);
@@ -137,8 +138,10 @@ swiotlb_init_with_default_size (size_t default_size)
 		      "Use dom0_mem Xen boot parameter to reserve\n"
 		      "some DMA memory (e.g., dom0_mem=-128M).\n");
 
-	xen_create_contiguous_region(
-		(unsigned long)iotlb_virt_start, get_order(bytes));
+	/* Hardcode 31 address bits for now: aacraid limitation. */
+	rc = xen_create_contiguous_region(
+		(unsigned long)iotlb_virt_start, get_order(bytes), 31);
+	BUG_ON(rc);
 
 	/*
 	 * Allocate and initialize the free list array.  This array is used

linux-2.6-xen-sparse/arch/xen/i386/mm/hypervisor.c

@@ -314,7 +314,8 @@ static void contiguous_bitmap_clear(
 }
 
 /* Ensure multi-page extents are contiguous in machine memory. */
-void xen_create_contiguous_region(unsigned long vstart, unsigned int order)
+int xen_create_contiguous_region(
+	unsigned long vstart, unsigned int order, unsigned int address_bits)
 {
 	pgd_t         *pgd; 
 	pud_t         *pud; 
@@ -349,9 +350,10 @@ void xen_create_contiguous_region(unsigned long vstart, unsigned int order)
 
 	/* 2. Get a new contiguous memory extent. */
 	reservation.extent_order = order;
-	reservation.address_bits = 31; /* aacraid limitation */
-	BUG_ON(HYPERVISOR_memory_op(
-		XENMEM_increase_reservation, &reservation) != 1);
+	reservation.address_bits = address_bits;
+	if (HYPERVISOR_memory_op(XENMEM_increase_reservation,
+				 &reservation) != 1)
+		goto fail;
 
 	/* 3. Map the new extent in place of old pages. */
 	for (i = 0; i < (1<<order); i++) {
@@ -367,6 +369,28 @@ void xen_create_contiguous_region(unsigned long vstart, unsigned int order)
 	contiguous_bitmap_set(__pa(vstart) >> PAGE_SHIFT, 1UL << order);
 
 	balloon_unlock(flags);
+
+	return 0;
+
+ fail:
+	reservation.extent_order = 0;
+	reservation.address_bits = 0;
+
+	for (i = 0; i < (1<<order); i++) {
+		BUG_ON(HYPERVISOR_memory_op(
+			XENMEM_increase_reservation, &reservation) != 1);
+		BUG_ON(HYPERVISOR_update_va_mapping(
+			vstart + (i*PAGE_SIZE),
+			pfn_pte_ma(mfn, PAGE_KERNEL), 0));
+		xen_machphys_update(mfn, (__pa(vstart)>>PAGE_SHIFT)+i);
+		phys_to_machine_mapping[(__pa(vstart)>>PAGE_SHIFT)+i] = mfn;
+	}
+
+	flush_tlb_all();
+
+	balloon_unlock(flags);
+
+	return -ENOMEM;
 }
 
 void xen_destroy_contiguous_region(unsigned long vstart, unsigned int order)

linux-2.6-xen-sparse/arch/xen/i386/mm/pgtable.c

@@ -279,8 +279,9 @@ void pgd_ctor(void *pgd, kmem_cache_t *cache, unsigned long unused)
 	unsigned long flags;
 
 #ifdef CONFIG_X86_PAE
-	/* this gives us a page below 4GB */
-	xen_create_contiguous_region((unsigned long)pgd, 0);
+	/* Ensure pgd resides below 4GB. */
+	int rc = xen_create_contiguous_region((unsigned long)pgd, 0, 32);
+	BUG_ON(rc);
 #endif
 
 	if (!HAVE_SHARED_KERNEL_PMD)

linux-2.6-xen-sparse/arch/xen/kernel/skbuff.c

@@ -79,8 +79,10 @@ static void skbuff_ctor(void *buf, kmem_cache_t *cachep, unsigned long unused)
 	while (skbuff_order_cachep[order] != cachep)
 		order++;
 
+	/* Do our best to allocate contiguous memory but fall back to IOMMU. */
 	if (order != 0)
-		xen_create_contiguous_region((unsigned long)buf, order);
+		(void)xen_create_contiguous_region(
+			(unsigned long)buf, order, 0);
 
 	scrub_pages(buf, 1 << order);
 }

linux-2.6-xen-sparse/include/asm-xen/asm-i386/hypervisor.h

@@ -129,8 +129,11 @@ void xen_invlpg_mask(cpumask_t *mask, unsigned long ptr);
 #define EXPORT_PER_CPU_SYMBOL_GPL(var) EXPORT_SYMBOL_GPL(per_cpu__##var)
 #endif /* linux < 2.6.0 */
 
-void xen_create_contiguous_region(unsigned long vstart, unsigned int order);
-void xen_destroy_contiguous_region(unsigned long vstart, unsigned int order);
+/* Returns zero on success else negative errno. */
+int xen_create_contiguous_region(
+    unsigned long vstart, unsigned int order, unsigned int address_bits);
+void xen_destroy_contiguous_region(
+    unsigned long vstart, unsigned int order);
 
 #include <asm/hypercall.h>