[Xen-devel] [PATCH v2 2/2] x86/xen: dont add memory above max allowed allocation

[Juergen Gross <jgross@xxxxxxxx>]

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@xxxxxxxx>
---
 arch/x86/xen/setup.c      | 10 ++++++++++
 drivers/xen/xen-balloon.c |  6 ++++++
 2 files changed, 16 insertions(+)

diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index d5f303c0e656..fdb184cadaf5 100644
--- a/arch/x86/xen/setup.c
+++ b/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>
@@ -825,6 +826,15 @@ char * __init xen_memory_setup(void)
                                xen_max_p2m_pfn = pfn_s + n_pfns;
                        } else
                                discard = true;
+#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 = xen_e820_table.entries[i].addr +
+                                      xen_e820_table.entries[i].size;
+#endif
                }
 
                if (!discard)
diff --git a/drivers/xen/xen-balloon.c b/drivers/xen/xen-balloon.c
index 2acbfe104e46..2a960fcc812e 100644
--- a/drivers/xen/xen-balloon.c
+++ b/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>
@@ -63,6 +64,11 @@ 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. */
+       max_mem_size = U64_MAX;
+#endif
+
        err = xenbus_scanf(XBT_NIL, "memory", "target", "%llu", &new_target);
        if (err != 1) {
                /* This is ok (for domain0 at least) - so just return */
-- 
2.16.4


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