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

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Date:   Wed, 30 Jan 2019 09:22:33 +0100
From:   Juergen Gross <jgross@...e.com>
To:     linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
        x86@...nel.org, linux-mm@...ck.org
Cc:     boris.ostrovsky@...cle.com, sstabellini@...nel.org, hpa@...or.com,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        Juergen Gross <jgross@...e.com>
Subject: [PATCH v2 2/2] 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@...e.com>
---
 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