From: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Date: Fri, 29 Mar 2013 01:14:00 +0000 (+0800)
Subject: xen: mask x2APIC feature in PV
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=4ea9b9aca90cfc71e6872ed3522356755162932c;p=linux.git
xen: mask x2APIC feature in PV
On x2apic enabled pvm, doing sysrq+l, got NULL pointer dereference as below.
SysRq : Show backtrace of all active CPUs
BUG: unable to handle kernel NULL pointer dereference at (null)
IP: [<ffffffff8125e3cb>] memcpy+0xb/0x120
Call Trace:
[<ffffffff81039633>] ? __x2apic_send_IPI_mask+0x73/0x160
[<ffffffff8103973e>] x2apic_send_IPI_all+0x1e/0x20
[<ffffffff8103498c>] arch_trigger_all_cpu_backtrace+0x6c/0xb0
[<ffffffff81501be4>] ? _raw_spin_lock_irqsave+0x34/0x50
[<ffffffff8131654e>] sysrq_handle_showallcpus+0xe/0x10
[<ffffffff8131616d>] __handle_sysrq+0x7d/0x140
[<ffffffff81316230>] ? __handle_sysrq+0x140/0x140
[<ffffffff81316287>] write_sysrq_trigger+0x57/0x60
[<ffffffff811ca996>] proc_reg_write+0x86/0xc0
[<ffffffff8116dd8e>] vfs_write+0xce/0x190
[<ffffffff8116e3e5>] sys_write+0x55/0x90
[<ffffffff8150a242>] system_call_fastpath+0x16/0x1b
That's because apic points to apic_x2apic_cluster or apic_x2apic_phys
but the basic element like cpumask isn't initialized.
Mask x2APIC feature in pvm to avoid overwrite of apic pointer,
update commit message per Konrad's suggestion.
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Tested-by: Tamon Shiose <tamon.shiose@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 31e19f97fb5ae..4bd0066a1ef05 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -429,6 +429,9 @@ static void __init xen_init_cpuid_mask(void)
cpuid_leaf1_edx_mask &=
~((1 << X86_FEATURE_APIC) | /* disable local APIC */
(1 << X86_FEATURE_ACPI)); /* disable ACPI */
+
+ cpuid_leaf1_ecx_mask &= ~(1 << (X86_FEATURE_X2APIC % 32));
+
ax = 1;
cx = 0;
xen_cpuid(&ax, &bx, &cx, &dx);