x86/xen: dont add memory above max allowed allocation

Don't allow memory to be added above the allowed maximum allocation
limit set by Xen.

Trying to do so would result in cases like the following:

[  584.559652] ------------[ cut here ]------------
[  584.564897] WARNING: CPU: 2 PID: 1 at ../arch/x86/xen/multicalls.c:129 xen_alloc_pte+0x1c7/0x390()
[  584.575151] Modules linked in:
[  584.578643] Supported: Yes
[  584.581750] CPU: 2 PID: 1 Comm: swapper/0 Not tainted 4.4.120-92.70-default #1
[  584.590000] Hardware name: Cisco Systems Inc UCSC-C460-M4/UCSC-C460-M4, BIOS C460M4.4.0.1b.0.0629181419 06/29/2018
[  584.601862]  0000000000000000 ffffffff813175a0 0000000000000000 ffffffff8184777c
[  584.610200]  ffffffff8107f4e1 ffff880487eb7000 ffff8801862b79c0 ffff88048608d290
[  584.618537]  0000000000487eb7 ffffea0000000201 ffffffff81009de7 ffffffff81068561
[  584.626876] Call Trace:
[  584.629699]  [<ffffffff81019ad9>] dump_trace+0x59/0x340
[  584.635645]  [<ffffffff81019eaa>] show_stack_log_lvl+0xea/0x170
[  584.642391]  [<ffffffff8101ac51>] show_stack+0x21/0x40
[  584.648238]  [<ffffffff813175a0>] dump_stack+0x5c/0x7c
[  584.654085]  [<ffffffff8107f4e1>] warn_slowpath_common+0x81/0xb0
[  584.660932]  [<ffffffff81009de7>] xen_alloc_pte+0x1c7/0x390
[  584.667289]  [<ffffffff810647f0>] pmd_populate_kernel.constprop.6+0x40/0x80
[  584.675241]  [<ffffffff815ecfe8>] phys_pmd_init+0x210/0x255
[  584.681587]  [<ffffffff815ed207>] phys_pud_init+0x1da/0x247
[  584.687931]  [<ffffffff815edb3b>] kernel_physical_mapping_init+0xf5/0x1d4
[  584.695682]  [<ffffffff815e9bdd>] init_memory_mapping+0x18d/0x380
[  584.702631]  [<ffffffff81064699>] arch_add_memory+0x59/0xf0
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Juergen Gross <jgross@suse.com>

arch/x86/xen/setup.c

@@ -12,6 +12,7 @@
 #include <linux/memblock.h>
 #include <linux/cpuidle.h>
 #include <linux/cpufreq.h>
+#include <linux/memory_hotplug.h>
 
 #include <asm/elf.h>
 #include <asm/vdso.h>
@@ -589,6 +590,14 @@ static void __init xen_align_and_add_e820_region(phys_addr_t start,
 	if (type == E820_TYPE_RAM) {
 		start = PAGE_ALIGN(start);
 		end &= ~((phys_addr_t)PAGE_SIZE - 1);
+#ifdef CONFIG_MEMORY_HOTPLUG
+		/*
+		 * Don't allow adding memory not in E820 map while booting the
+		 * system. Once the balloon driver is up it will remove that
+		 * restriction again.
+		 */
+		max_mem_size = end;
+#endif
 	}
 
 	e820__range_add(start, end - start, type);
@@ -748,6 +757,10 @@ char * __init xen_memory_setup(void)
 	memmap.nr_entries = ARRAY_SIZE(xen_e820_table.entries);
 	set_xen_guest_handle(memmap.buffer, xen_e820_table.entries);
 
+#if defined(CONFIG_MEMORY_HOTPLUG) && defined(CONFIG_XEN_BALLOON)
+	xen_saved_max_mem_size = max_mem_size;
+#endif
+
 	op = xen_initial_domain() ?
 		XENMEM_machine_memory_map :
 		XENMEM_memory_map;

drivers/xen/xen-balloon.c

@@ -37,6 +37,7 @@
 #include <linux/mm_types.h>
 #include <linux/init.h>
 #include <linux/capability.h>
+#include <linux/memory_hotplug.h>
 
 #include <xen/xen.h>
 #include <xen/interface/xen.h>
@@ -50,6 +51,10 @@
 
 #define BALLOON_CLASS_NAME "xen_memory"
 
+#ifdef CONFIG_MEMORY_HOTPLUG
+u64 xen_saved_max_mem_size = 0;
+#endif
+
 static struct device balloon_dev;
 
 static int register_balloon(struct device *dev);
@@ -63,6 +68,12 @@ static void watch_target(struct xenbus_watch *watch,
 	static bool watch_fired;
 	static long target_diff;
 
+#ifdef CONFIG_MEMORY_HOTPLUG
+	/* The balloon driver will take care of adding memory now. */
+	if (xen_saved_max_mem_size)
+		max_mem_size = xen_saved_max_mem_size;
+#endif
+
 	err = xenbus_scanf(XBT_NIL, "memory", "target", "%llu", &new_target);
 	if (err != 1) {
 		/* This is ok (for domain0 at least) - so just return */

include/xen/xen.h

@@ -46,4 +46,8 @@ struct bio_vec;
 bool xen_biovec_phys_mergeable(const struct bio_vec *vec1,
 		const struct bio_vec *vec2);
 
+#if defined(CONFIG_MEMORY_HOTPLUG) && defined(CONFIG_XEN_BALLOON)
+extern u64 xen_saved_max_mem_size;
+#endif
+
 #endif	/* _XEN_XEN_H */