On Thu, Mar 16, 2023 at 5:43 PM Roger Pau Monne <roger.pau@xxxxxxxxxx> 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. Such checking is done using the existing information fetched
> by the Xen pCPU subsystem, extending it to also store the ACPI ID.
>
> 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 v3:
> - Protect xen_processor_present() definition with CONFIG_ACPI.
>
> Changes since v2:
> - Extend and use the existing pcpu functionality.
>
> Changes since v1:
> - Reword commit message.
> ---
> arch/x86/include/asm/xen/hypervisor.h | 10 ++++++++++
> drivers/acpi/processor_pdc.c | 11 +++++++++++
> drivers/xen/pcpu.c | 21 +++++++++++++++++++++
> 3 files changed, 42 insertions(+)
>
> diff --git a/arch/x86/include/asm/xen/hypervisor.h b/arch/x86/include/asm/xen/hypervisor.h
> index 5fc35f889cd1..990a1609677e 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
>
> +#if defined(CONFIG_XEN_DOM0) && defined(CONFIG_ACPI)
> +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/drivers/acpi/processor_pdc.c b/drivers/acpi/processor_pdc.c
> index 8c3f82c9fff3..18fb04523f93 100644
> --- a/drivers/acpi/processor_pdc.c
> +++ b/drivers/acpi/processor_pdc.c
> @@ -14,6 +14,8 @@
> #include <linux/acpi.h>
> #include <acpi/processor.h>
>
> +#include <xen/xen.h>
This along with the definition above is evidently insufficient for
xen_processor_present() to always be defined. See
https://lore.kernel.org/linux-acpi/64198b60.bO+m9o5w+Hd8hcF3%25lkp@xxxxxxxxx/T/#u
for example.
I'm dropping the patch now, please fix and resend.
> +
> #include "internal.h"
>
> static bool __init processor_physically_present(acpi_handle handle)
> @@ -47,6 +49,15 @@ static bool __init processor_physically_present(acpi_handle handle)
> return false;
> }
>
> + if (xen_initial_domain())
> + /*
> + * When running as a Xen dom0 the number of processors Linux
> + * sees can be different from the real number of processors on
> + * the system, and we still need to execute _PDC for all of
> + * them.
> + */
> + return xen_processor_present(acpi_id);
> +
> type = (acpi_type == ACPI_TYPE_DEVICE) ? 1 : 0;
> cpuid = acpi_get_cpuid(handle, type, acpi_id);
>
> diff --git a/drivers/xen/pcpu.c b/drivers/xen/pcpu.c
> index fd3a644b0855..034d05e56507 100644
> --- a/drivers/xen/pcpu.c
> +++ b/drivers/xen/pcpu.c
> @@ -58,6 +58,7 @@ struct pcpu {
> struct list_head list;
> struct device dev;
> uint32_t cpu_id;
> + uint32_t acpi_id;
> uint32_t flags;
> };
>
> @@ -249,6 +250,7 @@ static struct pcpu *create_and_register_pcpu(struct xenpf_pcpuinfo *info)
>
> INIT_LIST_HEAD(&pcpu->list);
> pcpu->cpu_id = info->xen_cpuid;
> + pcpu->acpi_id = info->acpi_id;
> pcpu->flags = info->flags;
>
> /* Need hold on xen_pcpu_lock before pcpu list manipulations */
> @@ -381,3 +383,22 @@ static int __init xen_pcpu_init(void)
> return ret;
> }
> arch_initcall(xen_pcpu_init);
> +
> +#ifdef CONFIG_ACPI
> +bool __init xen_processor_present(uint32_t acpi_id)
> +{
> + struct pcpu *pcpu;
> + bool online = false;
> +
> + mutex_lock(&xen_pcpu_lock);
> + list_for_each_entry(pcpu, &xen_pcpus, list)
> + if (pcpu->acpi_id == acpi_id) {
> + online = pcpu->flags & XEN_PCPU_FLAGS_ONLINE;
> + break;
> + }
> +
> + mutex_unlock(&xen_pcpu_lock);
> +
> + return online;
> +}
> +#endif
> --
> 2.39.0
>
