I'll see what I can do about building and installing 3.0 but I'm not holding out hope for a fix. I downloaded the code already and looked at the reboot path and is pretty much the same.

I've added debug code to Xen and I can see the BIOS is reporting I/O port address 0x64 is the reset port with a value of 0xFE. however, once that port write is issued, the system does not return. I also tried keyboard and triple fault and neither caused a reset. Shutdown works fine.

(XEN) Virgin FADT table
(XEN) 0000: 46 41 43 50 F4 00 00 00 04 6F 44 45 4C 4C 20 20
(XEN) 0010: 43 42 58 33 20 20 20 00 04 20 22 06 4D 53 46 54
(XEN) 0020: 13 00 01 00 40 4E FE 78 18 D0 F6 78 01 02 09 00
(XEN) 0030: B2 00 00 00 A0 A1 00 80 00 04 00 00 00 00 00 00
(XEN) 0040: 04 04 00 00 00 00 00 00 50 04 00 00 08 04 00 00
(XEN) 0050: 20 04 00 00 00 00 00 00 04 02 01 04 10 00 00 85
(XEN) 0060: 65 00 E9 03 00 04 10 00 01 03 7D 7E 32 13 00 00
(XEN) 0070: A5 86 03 00 01 08 00 00 64 00 00 00 00 00 00 00
(XEN) 0080: FE 00 00 00 40 4D FE 78 00 00 00 00 18 D0 F6 78
(XEN) 0090: 00 00 00 00 01 20 00 00 00 04 00 00 00 00 00 00
(XEN) 00A0: 01 00 00 00 00 00 00 00 00 00 00 00 01 10 00 00
(XEN) 00B0: 04 04 00 00 00 00 00 00 01 00 00 00 00 00 00 00
(XEN) 00C0: 00 00 00 00 01 08 00 00 50 04 00 00 00 00 00 00
(XEN) 00D0: 01 20 00 00 08 04 00 00 00 00 00 00 01 80 00 00
(XEN) 00E0: 20 04 00 00 00 00 00 00 01 00 00 00 00 00 00 00
(XEN) 00F0: 00 00 00 00
(XEN)
(XEN) signature: FACP
(XEN) length = 0x000000f4
(XEN) revision = 0x04
(XEN) checksum = 0x6foem_id: DELL oem_table_id: CBX3
(XEN) oem_revision = 0x06222004MSFT
(XEN) asl_compiler_revision = 0x00010013
(XEN) facs = 0x78fe4e40
(XEN) dsdt = 0x78f6d018
(XEN) model = 0x01
(XEN) preferred_profile = 0x02
(XEN) sci_interrupt = 0x0009
(XEN) smi_command = 0x000000b2
(XEN) acpi_enable = 0xa0
(XEN) acpi_disable = 0xa1
(XEN) S4bios_request = 0x00
(XEN) pstate_control = 0x80
(XEN) pm1a_event_block = 0x00000400
(XEN) pm1b_event_block = 0x00000000
(XEN) pm1a_control_block = 0x00000404
(XEN) pm1b_control_block = 0x00000000
(XEN) pm_timer_block = 0x00000408
(XEN) gpe0_block = 0x00000420
(XEN) gpe1_block = 0x00000000
(XEN) pm1_event_length = 0x04
(XEN) pm1_control_length = 0x02
(XEN) pm2_control_length = 0x01
(XEN) pm_timer_length = 0x04
(XEN) gpe0_block_length = 0x10
(XEN) gpe1_block_length = 0x00
(XEN) gpe1_base = 0x00
(XEN) cst_control = 0x85
(XEN) C2latency = 0x0065
(XEN) C3latency = 0x03e9
(XEN) flush_size = 0x0400
(XEN) flush_stride = 0x0010
(XEN) duty_offset = 0x01
(XEN) duty_width = 0x03
(XEN) day_alarm = 0x7d
(XEN) month_alarm = 0x7e
(XEN) century = 0x32
(XEN) boot_flags = 0x0013
(XEN) reserved = 0x00
(XEN) flags = 0x000386a5
(XEN) space_id = 0x01
(XEN) bit_width = 0x08
(XEN) bit_offset = 0x00
(XEN) access_width = 0x00
(XEN) address = 0x0000000000000064
(XEN) reset_value = 0xfe
(XEN) reserved4[0] = 0x00
(XEN) reserved4[1] = 0x00
(XEN) reserved4[2] = 0x00
(XEN) Xfacs = 0x0000000078fe4d40
(XEN) Xdsdt = 0x0000000078f6d018