Re: [Xen-devel] [RFC PATCH 3/5] Tool/ACPI: DSDT extension to support more vcpus

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Thu, Aug 24, 2017 at 10:52:18PM -0400, Lan Tianyu wrote:
> This patch is to change DSDT table for processor object to support >255 vcpus.

The note in ACPI 6.1A spec section 5.2.12.12 contains the following:

[Compatibility note] On some legacy OSes, Logical processors with APIC
ID values less than 255 (whether in XAPIC or X2APIC mode) must use the
Processor Local APIC structure to convey their APIC information to
OSPM, and those processors must be declared in the DSDT using the
Processor() keyword. Logical processors with APIC ID values 255 and
greater must use the Processor Local x2APIC structure and be declared
using the Device() keyword. See Section 19.6.102 "Processor (Declare
Processor)" for more information.

So you cannot unconditionally switch to using the Device for all
processors.

vCPUs <= 128 need to use the Processor keyword, while vCPUs > 128 need
to use the Device keyword.

FWIW the code below to create the Devices looks fine to me.

Roger.

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