3366cdb6d3
The command 'xl vcpu-set 0 0', issued in dom0, will crash dom0: BUG: unable to handle kernel NULL pointer dereference at 00000000000002d8 PGD 0 P4D 0 Oops: 0000 [#1] PREEMPT SMP NOPTI CPU: 7 PID: 65 Comm: xenwatch Not tainted 4.19.0-rc2-1.ga9462db-default #1 openSUSE Tumbleweed (unreleased) Hardware name: Intel Corporation S5520UR/S5520UR, BIOS S5500.86B.01.00.0050.050620101605 05/06/2010 RIP: e030:device_offline+0x9/0xb0 Code: 77 24 00 e9 ce fe ff ff 48 8b 13 e9 68 ff ff ff 48 8b 13 e9 29 ff ff ff 48 8b 13 e9 ea fe ff ff 90 66 66 66 66 90 41 54 55 53 <f6> 87 d8 02 00 00 01 0f 85 88 00 00 00 48 c7 c2 20 09 60 81 31 f6 RSP: e02b:ffffc90040f27e80 EFLAGS: 00010203 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 RDX: ffff8801f3800000 RSI: ffffc90040f27e70 RDI: 0000000000000000 RBP: 0000000000000000 R08: ffffffff820e47b3 R09: 0000000000000000 R10: 0000000000007ff0 R11: 0000000000000000 R12: ffffffff822e6d30 R13: dead000000000200 R14: dead000000000100 R15: ffffffff8158b4e0 FS: 00007ffa595158c0(0000) GS:ffff8801f39c0000(0000) knlGS:0000000000000000 CS: e033 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00000000000002d8 CR3: 00000001d9602000 CR4: 0000000000002660 Call Trace: handle_vcpu_hotplug_event+0xb5/0xc0 xenwatch_thread+0x80/0x140 ? wait_woken+0x80/0x80 kthread+0x112/0x130 ? kthread_create_worker_on_cpu+0x40/0x40 ret_from_fork+0x3a/0x50 This happens because handle_vcpu_hotplug_event is called twice. In the first iteration cpu_present is still true, in the second iteration cpu_present is false which causes get_cpu_device to return NULL. In case of cpu#0, cpu_online is apparently always true. Fix this crash by checking if the cpu can be hotplugged, which is false for a cpu that was just removed. Also check if the cpu was actually offlined by device_remove, otherwise leave the cpu_present state as it is. Rearrange to code to do all work with device_hotplug_lock held. Signed-off-by: Olaf Hering <olaf@aepfle.de> Reviewed-by: Juergen Gross <jgross@suse.com> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
124 lines
2.3 KiB
C
124 lines
2.3 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#define pr_fmt(fmt) "xen:" KBUILD_MODNAME ": " fmt
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#include <linux/notifier.h>
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#include <xen/xen.h>
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#include <xen/xenbus.h>
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#include <asm/xen/hypervisor.h>
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#include <asm/cpu.h>
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static void enable_hotplug_cpu(int cpu)
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{
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if (!cpu_present(cpu))
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xen_arch_register_cpu(cpu);
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set_cpu_present(cpu, true);
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}
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static void disable_hotplug_cpu(int cpu)
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{
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if (!cpu_is_hotpluggable(cpu))
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return;
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lock_device_hotplug();
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if (cpu_online(cpu))
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device_offline(get_cpu_device(cpu));
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if (!cpu_online(cpu) && cpu_present(cpu)) {
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xen_arch_unregister_cpu(cpu);
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set_cpu_present(cpu, false);
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}
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unlock_device_hotplug();
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}
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static int vcpu_online(unsigned int cpu)
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{
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int err;
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char dir[16], state[16];
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sprintf(dir, "cpu/%u", cpu);
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err = xenbus_scanf(XBT_NIL, dir, "availability", "%15s", state);
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if (err != 1) {
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if (!xen_initial_domain())
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pr_err("Unable to read cpu state\n");
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return err;
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}
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if (strcmp(state, "online") == 0)
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return 1;
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else if (strcmp(state, "offline") == 0)
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return 0;
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pr_err("unknown state(%s) on CPU%d\n", state, cpu);
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return -EINVAL;
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}
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static void vcpu_hotplug(unsigned int cpu)
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{
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if (!cpu_possible(cpu))
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return;
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switch (vcpu_online(cpu)) {
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case 1:
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enable_hotplug_cpu(cpu);
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break;
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case 0:
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disable_hotplug_cpu(cpu);
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break;
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default:
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break;
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}
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}
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static void handle_vcpu_hotplug_event(struct xenbus_watch *watch,
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const char *path, const char *token)
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{
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unsigned int cpu;
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char *cpustr;
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cpustr = strstr(path, "cpu/");
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if (cpustr != NULL) {
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sscanf(cpustr, "cpu/%u", &cpu);
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vcpu_hotplug(cpu);
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}
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}
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static int setup_cpu_watcher(struct notifier_block *notifier,
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unsigned long event, void *data)
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{
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int cpu;
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static struct xenbus_watch cpu_watch = {
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.node = "cpu",
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.callback = handle_vcpu_hotplug_event};
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(void)register_xenbus_watch(&cpu_watch);
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for_each_possible_cpu(cpu) {
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if (vcpu_online(cpu) == 0) {
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(void)cpu_down(cpu);
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set_cpu_present(cpu, false);
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}
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}
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return NOTIFY_DONE;
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}
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static int __init setup_vcpu_hotplug_event(void)
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{
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static struct notifier_block xsn_cpu = {
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.notifier_call = setup_cpu_watcher };
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#ifdef CONFIG_X86
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if (!xen_pv_domain() && !xen_pvh_domain())
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#else
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if (!xen_domain())
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#endif
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return -ENODEV;
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register_xenstore_notifier(&xsn_cpu);
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return 0;
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}
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arch_initcall(setup_vcpu_hotplug_event);
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