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

[Jason Andryuk <jason.andryuk@xxxxxxx>]

On 2025-03-25 12:17, Jan Beulich wrote:
> 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?
Wow, I'm surprised you found that :)  Yes, that is a build-time 
dependency, but the runtime dependency is only on xen_initial_domain(). 
Yes, it deserves updating.
Thanks,
Jason