Re: [PATCH 1/3] acpi/processor: fix evaluating _PDC method when running as Xen dom0

[Josef Johansson <josef@oderland.se>]

On 11/21/22 11:21, Roger Pau Monne wrote:
> When running as a Xen dom0 the number of CPUs available to Linux can
> be different from the number of CPUs present on the system, but in
> order to properly fetch processor performance related data _PDC must
> be executed on all the physical CPUs online on the system.
>
> The current checks in processor_physically_present() result in some
> processor objects not getting their _PDC methods evaluated when Linux
> is running as Xen dom0.  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.
>
> Fixes: 5d554a7bb064 ('ACPI: processor: add internal processor_physically_present()')
> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> ---
>   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 16f548a661cf..b9f512138043 100644
> --- a/arch/x86/include/asm/xen/hypervisor.h
> +++ b/arch/x86/include/asm/xen/hypervisor.h
> @@ -61,4 +61,14 @@ 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;
> +}
My compiler (Default GCC on Fedora 32, compiling for Qubes) complain 
loudly that the below was missing.

+}
+EXPORT_SYMBOL(xen_processor_present);

`ERROR: MODPOST xen_processor_present 
[drivers/xen/xen-acpi-processor.ko] undefined!`

Same thing with xen_sanitize_pdc in the next patch.

+}
+EXPORT_SYMBOL(xen_sanitize_pdc);

Everything compiled fine after those changes.
> +#endif
> 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>
> +
>   #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);
>