xen: allow extra memory to be in multiple regions

Allow the extra memory (used by the balloon driver) to be in multiple
regions (typically two regions, one for low memory and one for high
memory).  This allows the balloon driver to increase the number of
available low pages (if the initial number if pages is small).

As a side effect, the algorithm for building the e820 memory map is
simpler and more obviously correct as the map supplied by the
hypervisor is (almost) used as is (in particular, all reserved regions
and gaps are preserved).  Only RAM regions are altered and RAM regions
above max_pfn + extra_pages are marked as unused (the region is split
in two if necessary).

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

arch/x86/xen/setup.c

@@ -54,26 +54,32 @@ unsigned long xen_released_pages;
  */
 #define EXTRA_MEM_RATIO		(10)
 
-static void __init xen_add_extra_mem(unsigned long pages)
+static void __init xen_add_extra_mem(u64 start, u64 size)
 {
 	unsigned long pfn;
+	int i;
 
-	u64 size = (u64)pages * PAGE_SIZE;
-	u64 extra_start = xen_extra_mem[0].start + xen_extra_mem[0].size;
-
-	if (!pages)
-		return;
-
-	e820_add_region(extra_start, size, E820_RAM);
-	sanitize_e820_map(e820.map, ARRAY_SIZE(e820.map), &e820.nr_map);
-
-	memblock_x86_reserve_range(extra_start, extra_start + size, "XEN EXTRA");
+	for (i = 0; i < XEN_EXTRA_MEM_MAX_REGIONS; i++) {
+		/* Add new region. */
+		if (xen_extra_mem[i].size == 0) {
+			xen_extra_mem[i].start = start;
+			xen_extra_mem[i].size  = size;
+			break;
+		}
+		/* Append to existing region. */
+		if (xen_extra_mem[i].start + xen_extra_mem[i].size == start) {
+			xen_extra_mem[i].size += size;
+			break;
+		}
+	}
+	if (i == XEN_EXTRA_MEM_MAX_REGIONS)
+		printk(KERN_WARNING "Warning: not enough extra memory regions\n");
 
-	xen_extra_mem[0].size += size;
+	memblock_x86_reserve_range(start, start + size, "XEN EXTRA");
 
-	xen_max_p2m_pfn = PFN_DOWN(extra_start + size);
+	xen_max_p2m_pfn = PFN_DOWN(start + size);
 
-	for (pfn = PFN_DOWN(extra_start); pfn <= xen_max_p2m_pfn; pfn++)
+	for (pfn = PFN_DOWN(start); pfn <= xen_max_p2m_pfn; pfn++)
 		__set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
 }
 
@@ -120,8 +126,8 @@ static unsigned long __init xen_release_chunk(phys_addr_t start_addr,
 	return len;
 }
 
-static unsigned long __init xen_return_unused_memory(unsigned long max_pfn,
-						     const struct e820map *e820)
+static unsigned long __init xen_return_unused_memory(
+	unsigned long max_pfn, const struct e820entry *map, int nr_map)
 {
 	phys_addr_t max_addr = PFN_PHYS(max_pfn);
 	phys_addr_t last_end = ISA_END_ADDRESS;
@@ -129,13 +135,13 @@ static unsigned long __init xen_return_unused_memory(unsigned long max_pfn,
 	int i;
 
 	/* Free any unused memory above the low 1Mbyte. */
-	for (i = 0; i < e820->nr_map && last_end < max_addr; i++) {
-		phys_addr_t end = e820->map[i].addr;
+	for (i = 0; i < nr_map && last_end < max_addr; i++) {
+		phys_addr_t end = map[i].addr;
 		end = min(max_addr, end);
 
 		if (last_end < end)
 			released += xen_release_chunk(last_end, end);
-		last_end = max(last_end, e820->map[i].addr + e820->map[i].size);
+		last_end = max(last_end, map[i].addr + map[i].size);
 	}
 
 	if (last_end < max_addr)
@@ -200,20 +206,32 @@ static unsigned long __init xen_get_max_pages(void)
 	return min(max_pages, MAX_DOMAIN_PAGES);
 }
 
+static void xen_align_and_add_e820_region(u64 start, u64 size, int type)
+{
+	u64 end = start + size;
+
+	/* Align RAM regions to page boundaries. */
+	if (type == E820_RAM) {
+		start = PAGE_ALIGN(start);
+		end &= ~((u64)PAGE_SIZE - 1);
+	}
+
+	e820_add_region(start, end - start, type);
+}
+
 /**
  * machine_specific_memory_setup - Hook for machine specific memory setup.
  **/
 char * __init xen_memory_setup(void)
 {
 	static struct e820entry map[E820MAX] __initdata;
-	static struct e820entry map_raw[E820MAX] __initdata;
 
 	unsigned long max_pfn = xen_start_info->nr_pages;
 	unsigned long long mem_end;
 	int rc;
 	struct xen_memory_map memmap;
+	unsigned long max_pages;
 	unsigned long extra_pages = 0;
-	unsigned long extra_limit;
 	unsigned long identity_pages = 0;
 	int i;
 	int op;
@@ -240,49 +258,55 @@ char * __init xen_memory_setup(void)
 	}
 	BUG_ON(rc);
 
-	memcpy(map_raw, map, sizeof(map));
-	e820.nr_map = 0;
-	xen_extra_mem[0].start = mem_end;
-	for (i = 0; i < memmap.nr_entries; i++) {
-		unsigned long long end;
-
-		/* Guard against non-page aligned E820 entries. */
-		if (map[i].type == E820_RAM)
-			map[i].size -= (map[i].size + map[i].addr) % PAGE_SIZE;
-
-		end = map[i].addr + map[i].size;
-		if (map[i].type == E820_RAM && end > mem_end) {
-			/* RAM off the end - may be partially included */
-			u64 delta = min(map[i].size, end - mem_end);
-
-			map[i].size -= delta;
-			end -= delta;
-
-			extra_pages += PFN_DOWN(delta);
-			/*
-			 * Set RAM below 4GB that is not for us to be unusable.
-			 * This prevents "System RAM" address space from being
-			 * used as potential resource for I/O address (happens
-			 * when 'allocate_resource' is called).
-			 */
-			if (delta &&
-				(xen_initial_domain() && end < 0x100000000ULL))
-				e820_add_region(end, delta, E820_UNUSABLE);
+	/* Make sure the Xen-supplied memory map is well-ordered. */
+	sanitize_e820_map(map, memmap.nr_entries, &memmap.nr_entries);
+
+	max_pages = xen_get_max_pages();
+	if (max_pages > max_pfn)
+		extra_pages += max_pages - max_pfn;
+
+	xen_released_pages = xen_return_unused_memory(max_pfn, map,
+						      memmap.nr_entries);
+	extra_pages += xen_released_pages;
+
+	/*
+	 * Clamp the amount of extra memory to a EXTRA_MEM_RATIO
+	 * factor the base size.  On non-highmem systems, the base
+	 * size is the full initial memory allocation; on highmem it
+	 * is limited to the max size of lowmem, so that it doesn't
+	 * get completely filled.
+	 *
+	 * In principle there could be a problem in lowmem systems if
+	 * the initial memory is also very large with respect to
+	 * lowmem, but we won't try to deal with that here.
+	 */
+	extra_pages = min(EXTRA_MEM_RATIO * min(max_pfn, PFN_DOWN(MAXMEM)),
+			  extra_pages);
+
+	i = 0;
+	while (i < memmap.nr_entries) {
+		u64 addr = map[i].addr;
+		u64 size = map[i].size;
+		u32 type = map[i].type;
+
+		if (type == E820_RAM) {
+			if (addr < mem_end) {
+				size = min(size, mem_end - addr);
+			} else if (extra_pages) {
+				size = min(size, (u64)extra_pages * PAGE_SIZE);
+				extra_pages -= size / PAGE_SIZE;
+				xen_add_extra_mem(addr, size);
+			} else
+				type = E820_UNUSABLE;
 		}
 
-		if (map[i].size > 0 && end > xen_extra_mem[0].start)
-			xen_extra_mem[0].start = end;
+		xen_align_and_add_e820_region(addr, size, type);
 
-		/* Add region if any remains */
-		if (map[i].size > 0)
-			e820_add_region(map[i].addr, map[i].size, map[i].type);
+		map[i].addr += size;
+		map[i].size -= size;
+		if (map[i].size == 0)
+			i++;
 	}
-	/* Align the balloon area so that max_low_pfn does not get set
-	 * to be at the _end_ of the PCI gap at the far end (fee01000).
-	 * Note that the start of balloon area gets set in the loop above
-	 * to be past the last E820 region. */
-	if (xen_initial_domain() && (xen_extra_mem[0].start < (1ULL<<32)))
-		xen_extra_mem[0].start = (1ULL<<32);
 
 	/*
 	 * In domU, the ISA region is normal, usable memory, but we
@@ -308,45 +332,11 @@ char * __init xen_memory_setup(void)
 
 	sanitize_e820_map(e820.map, ARRAY_SIZE(e820.map), &e820.nr_map);
 
-	extra_limit = xen_get_max_pages();
-	if (max_pfn + extra_pages > extra_limit) {
-		if (extra_limit > max_pfn)
-			extra_pages = extra_limit - max_pfn;
-		else
-			extra_pages = 0;
-	}
-
-	xen_released_pages = xen_return_unused_memory(xen_start_info->nr_pages,
-						      &e820);
-	extra_pages += xen_released_pages;
-
-	/*
-	 * Clamp the amount of extra memory to a EXTRA_MEM_RATIO
-	 * factor the base size.  On non-highmem systems, the base
-	 * size is the full initial memory allocation; on highmem it
-	 * is limited to the max size of lowmem, so that it doesn't
-	 * get completely filled.
-	 *
-	 * In principle there could be a problem in lowmem systems if
-	 * the initial memory is also very large with respect to
-	 * lowmem, but we won't try to deal with that here.
-	 */
-	extra_limit = min(EXTRA_MEM_RATIO * min(max_pfn, PFN_DOWN(MAXMEM)),
-			  max_pfn + extra_pages);
-
-	if (extra_limit >= max_pfn)
-		extra_pages = extra_limit - max_pfn;
-	else
-		extra_pages = 0;
-
-	xen_add_extra_mem(extra_pages);
-
 	/*
 	 * Set P2M for all non-RAM pages and E820 gaps to be identity
-	 * type PFNs. We supply it with the non-sanitized version
-	 * of the E820.
+	 * type PFNs.
 	 */
-	identity_pages = xen_set_identity(map_raw, memmap.nr_entries);
+	identity_pages = xen_set_identity(e820.map, e820.nr_map);
 	printk(KERN_INFO "Set %ld page(s) to 1-1 mapping.\n", identity_pages);
 	return "Xen";
 }