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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 25.08.17 at 12:36, <roger.pau@xxxxxxxxxx> wrote:
> 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.

While changing this code, may I suggest to stop referring to the
128 vCPU boundary? The decision should be solely based on
LAPIC ID, such that the only place to change later on will end up
being the one where it gets set to double the vCPU number.

Jan


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