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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>
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@ -429,6 +429,9 @@ static void __init xen_init_cpuid_mask(void)
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cpuid_leaf1_edx_mask &=
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cpuid_leaf1_edx_mask &=
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~((1 << X86_FEATURE_APIC) | /* disable local APIC */
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~((1 << X86_FEATURE_APIC) | /* disable local APIC */
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(1 << X86_FEATURE_ACPI)); /* disable ACPI */
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(1 << X86_FEATURE_ACPI)); /* disable ACPI */
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cpuid_leaf1_ecx_mask &= ~(1 << (X86_FEATURE_X2APIC % 32));
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ax = 1;
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ax = 1;
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cx = 0;
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cx = 0;
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xen_cpuid(&ax, &bx, &cx, &dx);
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xen_cpuid(&ax, &bx, &cx, &dx);
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