On Wed, Mar 15, 2023 at 01:38:18PM +0100, Juergen Gross wrote:
> On 15.03.23 13:10, Roger Pau Monne wrote:
> > In ACPI systems, the OS can direct power management, as opposed to the
> > firmware. This OS-directed Power Management is called OSPM. Part of
> > telling the firmware that the OS going to direct power management is
> > making ACPI "_PDC" (Processor Driver Capabilities) calls. These _PDC
> > methods must be evaluated for every processor object. If these _PDC
> > calls are not completed for every processor it can lead to
> > inconsistency and later failures in things like the CPU frequency
> > driver.
> >
> > In a Xen system, the dom0 kernel is responsible for system-wide power
> > management. The dom0 kernel is in charge of OSPM. However, the
> > number of CPUs available to dom0 can be different than the number of
> > CPUs physically present on the system.
> >
> > This leads to a problem: the dom0 kernel needs to evaluate _PDC for
> > all the processors, but it can't always see them.
> >
> > In dom0 kernels, ignore the existing ACPI method for determining if a
> > processor is physically present because it might not be accurate.
> > Instead, ask the hypervisor for this information.
> >
> > Fix this by introducing a custom function to use when running as Xen
> > dom0 in order to check whether a processor object matches a CPU that's
> > online.
> >
> > This ensures that _PDC method gets evaluated for all physically online
> > CPUs, regardless of the number of CPUs made available to dom0.
> >
> > Fixes: 5d554a7bb064 ('ACPI: processor: add internal processor_physically_present()')
> > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> > ---
> > Changes since v1:
> > - Reword commit message.
> > ---
> > arch/x86/include/asm/xen/hypervisor.h | 10 ++++++++++
> > arch/x86/xen/enlighten.c | 27 +++++++++++++++++++++++++++
> > drivers/acpi/processor_pdc.c | 11 +++++++++++
> > 3 files changed, 48 insertions(+)
> >
> > diff --git a/arch/x86/include/asm/xen/hypervisor.h b/arch/x86/include/asm/xen/hypervisor.h
> > index 5fc35f889cd1..f14e39bce2cb 100644
> > --- a/arch/x86/include/asm/xen/hypervisor.h
> > +++ b/arch/x86/include/asm/xen/hypervisor.h
> > @@ -63,4 +63,14 @@ void __init xen_pvh_init(struct boot_params *boot_params);
> > void __init mem_map_via_hcall(struct boot_params *boot_params_p);
> > #endif
> > +#ifdef CONFIG_XEN_DOM0
> > +bool __init xen_processor_present(uint32_t acpi_id);
> > +#else
> > +static inline bool xen_processor_present(uint32_t acpi_id)
> > +{
> > + BUG();
> > + return false;
> > +}
> > +#endif
> > +
> > #endif /* _ASM_X86_XEN_HYPERVISOR_H */
> > diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> > index b8db2148c07d..d4c44361a26c 100644
> > --- a/arch/x86/xen/enlighten.c
> > +++ b/arch/x86/xen/enlighten.c
> > @@ -346,3 +346,30 @@ void xen_arch_unregister_cpu(int num)
> > }
> > EXPORT_SYMBOL(xen_arch_unregister_cpu);
> > #endif
> > +
> > +#ifdef CONFIG_XEN_DOM0
> > +bool __init xen_processor_present(uint32_t acpi_id)
> > +{
> > + unsigned int i, maxid;
> > + struct xen_platform_op op = {
> > + .cmd = XENPF_get_cpuinfo,
> > + .interface_version = XENPF_INTERFACE_VERSION,
> > + };
> > + int ret = HYPERVISOR_platform_op(&op);
> > +
> > + if (ret)
> > + return false;
> > +
> > + maxid = op.u.pcpu_info.max_present;
> > + for (i = 0; i <= maxid; i++) {
> > + op.u.pcpu_info.xen_cpuid = i;
> > + ret = HYPERVISOR_platform_op(&op);
> > + if (ret)
> > + continue;
> > + if (op.u.pcpu_info.acpi_id == acpi_id)
> > + return op.u.pcpu_info.flags & XEN_PCPU_FLAGS_ONLINE;
> > + }
> > +
> > + return false;
> > +}
> > +#endif
>
> Did you consider not to do the hypercall again and again, but to reuse the
> pcpu list from drivers/xen/pcpu.c instead? You'd need to store the acpi_id
> in this list, of course.
Oh, didn't know this was available. Seems to be initialized before
the _PDC evaluation, so I can give it a try.
Thanks, Roger.
