kmemcheck: OS boot failed because NMI handlers access the memory tracked by kmemcheck

[Xishi Qiu <qiuxishi@huawei.com>]

OS boot failed when set cmdline kmemcheck=1. The reason is that
NMI handlers will access the memory from kmalloc(), this will cause
page fault, because memory from kmalloc() is tracked by kmemcheck.

watchdog_nmi_enable()
	perf_event_create_kernel_counter()
		perf_event_alloc()
			event = kzalloc(sizeof(*event), GFP_KERNEL);

Now we don't support page faults in NMI context is that we
may already be handling an existing fault (or trap) when the NMI hits.
So that would mess up kmemcheck's working state.

Here is the failed log:
[    1.731052] WARNING: CPU: 0 PID: 1 at arch/x86/mm/kmemcheck/kmemcheck.c:634 k
memcheck_fault+0xb1/0xc0()
[    1.731053] Modules linked in:
[    1.731056] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.14.0-rc3-0.1-default+
 #1
[    1.731057] Hardware name: Huawei Technologies Co., Ltd. Tecal RH2285
  /BC11BTSA              , BIOS CTSAV036 04/27/2011
[    1.731061]  000000000000027a ffff880c39c07678 ffffffff814ca491 ffff880c39c07
6b8
[    1.731063]  ffffffff8104ce97 0000000000000000 ffff880c39c07838 ffff880c21028
1d4
[    1.731065]  0000000000000000 0000000000000000 ffff880c210281d4 ffff880c39c07
6c8
[    1.731065] Call Trace:
[    1.731073]  <NMI>  [<ffffffff814ca491>] dump_stack+0x6a/0x79
[    1.731077]  [<ffffffff8104ce97>] warn_slowpath_common+0x87/0xb0
[    1.731079]  [<ffffffff8104ced5>] warn_slowpath_null+0x15/0x20
[    1.731081]  [<ffffffff810452c1>] kmemcheck_fault+0xb1/0xc0
[    1.731087]  [<ffffffff814d262b>] __do_page_fault+0x39b/0x4c0
[    1.731092]  [<ffffffff81272cd2>] ? put_dec+0x72/0x90
[    1.731093]  [<ffffffff812730ba>] ? number+0x33a/0x360
[    1.731096]  [<ffffffff814d2829>] do_page_fault+0x9/0x10
[    1.731098]  [<ffffffff814cf222>] page_fault+0x22/0x30
[    1.731104]  [<ffffffff81348b4c>] ? vt_console_print+0x8c/0x400
[    1.731106]  [<ffffffff81348b2c>] ? vt_console_print+0x6c/0x400
[    1.731111]  [<ffffffff8109cd9b>] ? msg_print_text+0x18b/0x1f0
[    1.731113]  [<ffffffff8109bed1>] call_console_drivers+0xc1/0xe0
[    1.731115]  [<ffffffff8109d746>] console_unlock+0x236/0x280
[    1.731117]  [<ffffffff8109e095>] vprintk_emit+0x2b5/0x450
[    1.731119]  [<ffffffff810452c1>] ? kmemcheck_fault+0xb1/0xc0
[    1.731120]  [<ffffffff814ca3f7>] printk+0x4a/0x4c
[    1.731122]  [<ffffffff810452c1>] ? kmemcheck_fault+0xb1/0xc0
[    1.731124]  [<ffffffff8104ce4e>] warn_slowpath_common+0x3e/0xb0
[    1.731126]  [<ffffffff8104ced5>] warn_slowpath_null+0x15/0x20
[    1.731128]  [<ffffffff810452c1>] kmemcheck_fault+0xb1/0xc0
[    1.731130]  [<ffffffff814d262b>] __do_page_fault+0x39b/0x4c0
[    1.731132]  [<ffffffff814d2829>] do_page_fault+0x9/0x10
[    1.731134]  [<ffffffff814cf222>] page_fault+0x22/0x30
[    1.731138]  [<ffffffff81015b52>] ? x86_perf_event_update+0x2/0x70
[    1.731142]  [<ffffffff8101de21>] ? intel_pmu_save_and_restart+0x11/0x50
[    1.731144]  [<ffffffff8101eb02>] intel_pmu_handle_irq+0x142/0x3a0
[    1.731146]  [<ffffffff814d0655>] perf_event_nmi_handler+0x35/0x60
[    1.731148]  [<ffffffff814cfe83>] nmi_handle+0x63/0x150
[    1.731150]  [<ffffffff814cffd3>] default_do_nmi+0x63/0x290
[    1.731151]  [<ffffffff814d02a8>] do_nmi+0xa8/0xe0

Another NMI handler which from CONFIG_ACPI_APEI_GHES=y, has the same problem too.
ghes_probe()
	register_nmi_handler(NMI_LOCAL, ghes_notify_nmi, 0, "ghes");

I find it is not easy to change, because:
e.g.
ghes_ioremap_init()
	ghes_ioremap_area = __get_vm_area() -> it will call kmalloc() at last, and we 
						can not change the general interface. 

And we can not use kmem_cache_alloc()(create a new slab with SLAB_NOTRACK) instead of 
kmalloc() when the size is variable.

Thanks,
Xishi Qiu

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