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Message-ID: <CAJZ5v0jRNHDsDwXPJa01x2t35vNboVxb4hysE4dfThrJs9kT7Q@mail.gmail.com>
Date: Wed, 22 Mar 2023 19:39:43 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Roger Pau Monne <roger.pau@...rix.com>
Cc: linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
"Rafael J. Wysocki" <rafael@...nel.org>,
Len Brown <lenb@...nel.org>, Juergen Gross <jgross@...e.com>,
Stefano Stabellini <sstabellini@...nel.org>,
Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
Alex Chiang <achiang@...com>, linux-acpi@...r.kernel.org
Subject: Re: [PATCH v6] ACPI: processor: Fix evaluating _PDC method when
running as Xen dom0
On Wed, Mar 22, 2023 at 12:13 PM Roger Pau Monne <roger.pau@...rix.com> 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@...rix.com>
> ---
> Changes since v5:
> - Include bug.h header for the inline dummy helper.
> - Constify pcpu local variable in xen_processor_present().
>
> Changes since v4:
> - Move definition/declaration of xen_processor_present() to different
> header.
> - Fold subject edit.
>
> 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.
> ---
> drivers/acpi/processor_pdc.c | 11 +++++++++++
> drivers/xen/pcpu.c | 20 ++++++++++++++++++++
> include/xen/xen.h | 11 +++++++++++
> 3 files changed, 42 insertions(+)
>
> 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);
>
> diff --git a/drivers/xen/pcpu.c b/drivers/xen/pcpu.c
> index fd3a644b0855..b3e3d1bb37f3 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 +383,21 @@ 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)
> +{
> + const 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
> diff --git a/include/xen/xen.h b/include/xen/xen.h
> index 7adf59837c25..0efeb652f9b8 100644
> --- a/include/xen/xen.h
> +++ b/include/xen/xen.h
> @@ -71,4 +71,15 @@ static inline void xen_free_unpopulated_pages(unsigned int nr_pages,
> }
> #endif
>
> +#if defined(CONFIG_XEN_DOM0) && defined(CONFIG_ACPI) && defined(CONFIG_X86)
> +bool __init xen_processor_present(uint32_t acpi_id);
> +#else
> +#include <linux/bug.h>
> +static inline bool xen_processor_present(uint32_t acpi_id)
> +{
> + BUG();
> + return false;
> +}
> +#endif
> +
> #endif /* _XEN_XEN_H */
> --
Applied as 6.4 material.
I've added the R-by from Juergen to it, because the difference between
it and the v4 for which the tag was provided is merely a build fix.
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