Re: [PATCH v3 1/5] xen/acpi: upload power and performance related data from a PVH dom0

[Jan Beulich <jbeulich@xxxxxxxx>]

On 06.03.2025 12:08, Penny Zheng wrote:
> From: Roger Pau Monne <roger.pau@xxxxxxxxxx>
> 
> When running as a PVH dom0 the ACPI MADT is crafted by Xen in order to
> report the correct numbers of vCPUs that dom0 has, so the host MADT is
> not provided to dom0.  This creates issues when parsing the power and
> performance related data from ACPI dynamic tables, as the ACPI
> Processor UIDs found on the dynamic code are likely to not match the
> ones crafted by Xen in the dom0 MADT.
> 
> Xen would rely on Linux having filled at least the power and
> performance related data of the vCPUs on the system, and would clone
> that information in order to setup the remaining pCPUs on the system
> if dom0 vCPUs < pCPUs.  However when running as PVH dom0 it's likely
> that none of dom0 CPUs will have the power and performance data
> filled, and hence the Xen ACPI Processor driver needs to fetch that
> information by itself.
> 
> In order to do so correctly, introduce a new helper to fetch the _CST
> data without taking into account the system capabilities from the
> CPUID output, as the capabilities reported to dom0 in CPUID might be
> different from the ones on the host.
> 
> Note that the newly introduced code will only fetch the _CST, _PSS,
> _PPC and _PCT from a single CPU, and clone that information for all the
> other Processors.  This won't work on an heterogeneous system with
> Processors having different power and performance related data between
> them.
> 
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> Signed-off-by: Jason Andryuk <jason.andryuk@xxxxxxx>
> ---
>  drivers/xen/pcpu.c               |   3 +-
>  drivers/xen/xen-acpi-processor.c | 232 ++++++++++++++++++++++++++++---
>  include/xen/xen.h                |   2 +-
>  3 files changed, 216 insertions(+), 21 deletions(-)

No dependency on another patch is mentioned anywhere (the cover letter
only says the series is based on the very patch here), yet the bulk of
the changes here (to drivers/xen/xen-acpi-processor.c) are meaningless
for a PVH Dom0, because of

config XEN_ACPI_PROCESSOR
        tristate "Xen ACPI processor"
        depends on XEN && XEN_PV_DOM0 && X86 && ACPI_PROCESSOR && CPU_FREQ

(note the XEN_PV_DOM0 in there). Is the patch here perhaps missing an
adjustment to the above, to use XEN_DOM0 instead?

Jan