Comment 1 for bug 1951924

[SRU Justification]

[Impact]

Current linux-azure-4.15 kernel in bionic fails to boot Standard_M416s_v2 VM because of x2apic being disabled:

[ 0.000000] x2apic: IRQ remapping doesn't support X2APIC mode
[ 0.000000] unchecked MSR access error: WRMSR to 0x1b (tried to write 0x00000000fee00100) at rIP: 0xffffffff9325d1f8 (native_write_msr+0x8/0x30)
[ 0.000000] Call Trace:
[ 0.000000] __x2apic_disable.part.5+0x49/0x80
[ 0.000000] enable_IR_x2apic+0x123/0x18c
[ 0.000000] default_setup_apic_routing+0x16/0x73
[ 0.000000] apic_intr_mode_init+0x84/0x91
[ 0.000000] x86_late_time_init+0x24/0x2b
[ 0.000000] start_kernel+0x444/0x505
[ 0.000000] x86_64_start_reservations+0x24/0x26
[ 0.000000] x86_64_start_kernel+0x74/0x77
[ 0.000000] secondary_startup_64+0xa5/0xb0
[ 0.000000] x2apic disabled
[ 0.000000] Switched APIC routing to physical flat.

[Test Plan]

Run updated kernel (with x2apic support backported from linux-azure-5.4 kernel).

It should boot fine and display:

[ 0.000000] Setting APIC routing to physical x2apic.

[Where problems could occur]

Potentially x2apic may now be used on other VM instances.

[Other Info]

None.