RE: [PATCH RFC v3 20/21] ACPI: Add _OSC bits to advertise OS support for toggling CPU present/enabled

Jose Marinho
2024-01-02T15:35:49Z

> -----Original Message-----
> From: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
> Sent: Tuesday, January 2, 2024 3:17 PM
> To: Jose Marinho <Jose.Marinho@arm.com>
> Cc: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>; linux-
> pm@vger.kernel.org; loongarch@lists.linux.dev; linux-acpi@vger.kernel.org;
> linux-arch@vger.kernel.org; linux-kernel@vger.kernel.org; linux-arm-
> kernel@lists.infradead.org; linux-riscv@lists.infradead.org;
> kvmarm@lists.linux.dev; x86@kernel.org; acpica-
> devel@lists.linuxfoundation.org; linux-csky@vger.kernel.org; linux-
> doc@vger.kernel.org; linux-ia64@vger.kernel.org; linux-parisc@vger.kernel.org;
> Salil Mehta <salil.mehta@huawei.com>; Jean-Philippe Brucker <jean-
> philippe@linaro.org>; Jianyong Wu <Jianyong.Wu@arm.com>; Justin He
> <Justin.He@arm.com>; James Morse <James.Morse@arm.com>; Samer El-Haj-
> Mahmoud <Samer.El-Haj-Mahmoud@arm.com>; nd <nd@arm.com>; Kangkang
> Shen <kangkang.shen@futurewei.com>
> Subject: Re: [PATCH RFC v3 20/21] ACPI: Add _OSC bits to advertise OS support
> for toggling CPU present/enabled
>
> On Tue, 2 Jan 2024 13:07:25 +0000
> Jose Marinho <Jose.Marinho@arm.com> wrote:
>
> > Hi Jonathan,
> >
> > > -----Original Message-----
> > > From: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
> > > Sent: Friday, December 15, 2023 5:12 PM
> > > To: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
> > > Cc: linux-pm@vger.kernel.org; loongarch@lists.linux.dev; linux-
> > > acpi@vger.kernel.org; linux-arch@vger.kernel.org; linux-
> > > kernel@vger.kernel.org; linux-arm-kernel@lists.infradead.org; linux-
> > > riscv@lists.infradead.org; kvmarm@lists.linux.dev; x86@kernel.org;
> > > acpica- devel@lists.linuxfoundation.org; linux-csky@vger.kernel.org;
> > > linux- doc@vger.kernel.org; linux-ia64@vger.kernel.org; linux-
> > > parisc@vger.kernel.org; Salil Mehta <salil.mehta@huawei.com>;
> > > Jean-Philippe Brucker <jean-philippe@linaro.org>; Jianyong Wu
> > > <Jianyong.Wu@arm.com>; Justin He <Justin.He@arm.com>; James Morse
> > > <James.Morse@arm.com>; Jose Marinho <Jose.Marinho@arm.com>; Samer
> > > El-Haj-Mahmoud <Samer.El- Haj-Mahmoud@arm.com>
> > > Subject: Re: [PATCH RFC v3 20/21] ACPI: Add _OSC bits to advertise
> > > OS support for toggling CPU present/enabled
> > >
> > > On Wed, 13 Dec 2023 12:50:54 +0000
> > > Russell King (Oracle) <rmk+kernel@armlinux.org.uk> wrote:
> > >
> > > > From: James Morse <james.morse@arm.com>
> > > >
> > > > Platform firmware can disabled a CPU, or make it not-present by
> > > > making an eject-request notification, then waiting for the os to
> > > > make it offline
> > > OS
> > >
> > > > and call _EJx. After the firmware updates _STA with the new status.
> > > >
> > > > Not all operating systems support this. For arm64 making CPUs
> > > > not-present has never been supported. For all ACPI architectures,
> > > > making CPUs disabled has recently been added. Firmware can't know
> > > > what
> > > the OS has support for.
> > > >
> > > > Add two new _OSC bits to advertise whether the OS supports the
> > > > _STA enabled or present bits being toggled for CPUs. This will be
> > > > important for arm64 if systems that support physical CPU hotplug
> > > > ever appear as
> > > > arm64 linux doesn't currently support this, so firmware shouldn't try.
> > > >
> > > > Advertising this support to firmware is useful for cloud
> > > > orchestrators to know whether they can scale a particular VM by adding
> CPUs.
> > > >
> > > > Signed-off-by: James Morse <james.morse@arm.com>
> > > > Tested-by: Miguel Luis <miguel.luis@oracle.com>
> > > > Tested-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
> > > > Tested-by: Jianyong Wu <jianyong.wu@arm.com>
> > >
> > > I'm very much in favor of this _OSC but it hasn't been accepted yet I think...
> > > https://bugzilla.tianocore.org/show_bug.cgi?id=4481
> > >
> > > Jose? Github suggests you are the proposer on this.
> >
> > The addition of these _OSC bits was proposed by us on the forum in question.
> > The forum opted to pause the definition until additional practical information
> could be provided on the use-cases.
> >
> > If anyone is interested in progressing the _OSC bit definition, you are invited to
> express that interest in the Bugzilla ticket.
>
> I've poked around a bit and can't find any reference to how to actually get a
> bugzilla account bugzilla.tianocore.org. Any pointers? I'm sure I had one at one
> stage, but trying every plausible email address and the forgotten password link
> got me nowhere.
>

The procedure to get a new account is described here: https://github.com/tianocore/tianocore.github.io/wiki/Reporting-Issues
The immediate next steps are:
- Join https://edk2.groups.io/g/devel, and subscribe edk2 | devel group.
- Send the email with the detail reason to Bugzilla Admin (gaoliming@byosoft.com.cn) , this email address will be created as Bugzilla account.

> > Information that you should provide to increase the chances of the ticket being
> reopened:
> > - use-case for the new _OSC bits,
>
> Really annoying without it as a hypervisor can't query if a guest can do anything
> useful if the host does virtual CPU hotplug via this newly added route.
> Given this is new functionality and there is non trivial effort required by the host
> to instantiate such a CPU it would be nice to be able to find out if the feature is
> supported by the Guest OS without having to basically suck it an see with
> hypervisors having to do a trial hotplug just to see if it 'might' work.
>
> > - what breaks (if anything) without the proposed _OSC bits.
>
> Nothing breaks - you can merrily poke in hotplugged CPUs with the attendant
> creation of resources in the host and have them disappear into a black hole.
> That's ugly but not broken as such. Hopefully a hypervisor will not keep trying
> until the first attempt either succeeds or fails.
>
> >
> > We did receive additional comments:
> > - the proposed _OSC bits are not generic: the bits simply convey whether the
> guest OS understands CPU hot-plug, but it says nothing about the number of CPUs
> that the OS supports.
>
> If a guest says it supports this feature, you would hope it supports it for the
> number of CPUs that have the present bit set but the enabled not.
> I'd clarify that in the text rather than provide a means of querying the number of
> CPUs supported.
> Number wouldn't be sufficient anyway as it wouldn't indicate 'which' CPUs are
> supported.
> Nothing says they have to be contiguous or lowest IDs etc.
>
> > - There could be alternate schemes that do not rely on spec changes. E.g. there
> could be a hypervisor IMPDEF mechanism to describe if an OS image supports
> CPU hot-plug.
>
> Sigh. Yes, that could be done at the cost of every guest having to be made aware
> of every hypervisor impdef mechanism. Trying to avoid that mess is why I think
> an _OSC makes sense as then everyone can use the same control.
>
> No particular reason we should use ACPI at all for VMs :)
>
> >
> > >
> > > btw v4 looks ok but v5 in the tianocore github seems to have lost
> > > the actual OSC part.
> >
> > Agree that, if we do progress with this spec change, v4 is the correct formulation
> we should adopt.
> >
> Thanks for the update.
>
> Overall this is a question we need to resolve soon. If this code otherwise goes in
> linux without the OSC we will always need to support the 'suck it and see'
> approach as we'll never know if the guest fell down the hole. Thus if not added
> soon we might as well not add it at all and we'll all be looking at the code and
> thinking "that's ugly and shouldn't have been necessary" for years to come.
>
> +CC Kangkang as he might be able to help get this started again.

We're keen to support the progress of this ECR.

Regards,
Jose

>
> Jonathan
>
> > Regards,
> > Jose
> >
> > >
> > > Jonathan
> > >
> > > > ---
> > > > I'm assuming Loongarch machines do not support physical CPU hotplug.
> > > >
> > > > Changes since RFC v3:
> > > > * Drop ia64 changes
> > > > * Update James' comment below "---" to remove reference to ia64
> > > >
> > > > Outstanding comment:
> > > > https://lore.kernel.org/r/20230914175021.000018fd@Huawei.com
> > >
> > >
> > >
> > > > ---
> > > > arch/x86/Kconfig | 1 +
> > > > drivers/acpi/Kconfig | 9 +++++++++
> > > > drivers/acpi/acpi_processor.c | 14 +++++++++++++-
> > > > drivers/acpi/bus.c | 16 ++++++++++++++++
> > > > include/linux/acpi.h | 4 ++++
> > > > 5 files changed, 43 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index
> > > > 64fc7c475ab0..33fc4dcd950c 100644
> > > > --- a/arch/x86/Kconfig
> > > > +++ b/arch/x86/Kconfig
> > > > @@ -60,6 +60,7 @@ config X86
> > > > select ACPI_LEGACY_TABLES_LOOKUP if ACPI
> > > > select ACPI_SYSTEM_POWER_STATES_SUPPORT if ACPI
> > > > select ACPI_HOTPLUG_PRESENT_CPU if ACPI_PROCESSOR
> > > && HOTPLUG_CPU
> > > > + select ACPI_HOTPLUG_IGNORE_OSC if ACPI &&
> > > HOTPLUG_CPU
> > > > select ARCH_32BIT_OFF_T if X86_32
> > > > select ARCH_CLOCKSOURCE_INIT
> > > > select ARCH_CORRECT_STACKTRACE_ON_KRETPROBE
> > > > diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig index
> > > > 9c5a43d0aff4..020e7c0ab985 100644
> > > > --- a/drivers/acpi/Kconfig
> > > > +++ b/drivers/acpi/Kconfig
> > > > @@ -311,6 +311,15 @@ config ACPI_HOTPLUG_PRESENT_CPU
> > > > depends on ACPI_PROCESSOR && HOTPLUG_CPU
> > > > select ACPI_CONTAINER
> > > >
> > > > +config ACPI_HOTPLUG_IGNORE_OSC
> > > > + bool
> > > > + depends on ACPI_HOTPLUG_PRESENT_CPU
> > > > + help
> > > > + Ignore whether firmware acknowledged support for toggling the CPU
> > > > + present bit in _STA. Some architectures predate the _OSC bits, so
> > > > + firmware doesn't know to do this.
> > > > +
> > > > +
> > > > config ACPI_PROCESSOR_AGGREGATOR
> > > > tristate "Processor Aggregator"
> > > > depends on ACPI_PROCESSOR
> > > > diff --git a/drivers/acpi/acpi_processor.c
> > > > b/drivers/acpi/acpi_processor.c index ea12e70dfd39..5bb207a7a1dd
> > > > 100644
> > > > --- a/drivers/acpi/acpi_processor.c
> > > > +++ b/drivers/acpi/acpi_processor.c
> > > > @@ -182,6 +182,18 @@ static void __init
> > > > acpi_pcc_cpufreq_init(void) static void __init
> > > > acpi_pcc_cpufreq_init(void) {} #endif /*
> > > > CONFIG_X86 */
> > > >
> > > > +static bool acpi_processor_hotplug_present_supported(void)
> > > > +{
> > > > + if (!IS_ENABLED(CONFIG_ACPI_HOTPLUG_PRESENT_CPU))
> > > > + return false;
> > > > +
> > > > + /* x86 systems pre-date the _OSC bit */
> > > > + if (IS_ENABLED(CONFIG_ACPI_HOTPLUG_IGNORE_OSC))
> > > > + return true;
> > > > +
> > > > + return osc_sb_hotplug_present_support_acked;
> > > > +}
> > > > +
> > > > /* Initialization */
> > > > static int acpi_processor_make_present(struct acpi_processor *pr)
> > > > { @@ -189,7 +201,7 @@ static int
> > > > acpi_processor_make_present(struct
> > > acpi_processor *pr)
> > > > acpi_status status;
> > > > int ret;
> > > >
> > > > - if (!IS_ENABLED(CONFIG_ACPI_HOTPLUG_PRESENT_CPU)) {
> > > > + if (!acpi_processor_hotplug_present_supported()) {
> > > > pr_err_once("Changing CPU present bit is not supported\n");
> > > > return -ENODEV;
> > > > }
> > > > diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c index
> > > > 72e64c0718c9..7122450739d6 100644
> > > > --- a/drivers/acpi/bus.c
> > > > +++ b/drivers/acpi/bus.c
> > > > @@ -298,6 +298,13 @@
> > > > EXPORT_SYMBOL_GPL(osc_sb_native_usb4_support_confirmed);
> > > >
> > > > bool osc_sb_cppc2_support_acked;
> > > >
> > > > +/*
> > > > + * ACPI 6.? Proposed Operating System Capabilities for modifying
> > > > +CPU
> > > > + * present/enable.
> > > > + */
> > > > +bool osc_sb_hotplug_enabled_support_acked;
> > > > +bool osc_sb_hotplug_present_support_acked;
> > > > +
> > > > static u8 sb_uuid_str[] = "0811B06E-4A27-44F9-8D60-3CBBC22E7B48";
> > > > static void acpi_bus_osc_negotiate_platform_control(void)
> > > > {
> > > > @@ -346,6 +353,11 @@ static void
> > > > acpi_bus_osc_negotiate_platform_control(void)
> > > >
> > > > if (!ghes_disable)
> > > > capbuf[OSC_SUPPORT_DWORD] |= OSC_SB_APEI_SUPPORT;
> > > > +
> > > > + capbuf[OSC_SUPPORT_DWORD] |=
> > > OSC_SB_HOTPLUG_ENABLED_SUPPORT;
> > > > + if (IS_ENABLED(CONFIG_ACPI_HOTPLUG_PRESENT_CPU))
> > > > + capbuf[OSC_SUPPORT_DWORD] |=
> > > OSC_SB_HOTPLUG_PRESENT_SUPPORT;
> > > > +
> > > > if (ACPI_FAILURE(acpi_get_handle(NULL, "\\_SB", &handle)))
> > > > return;
> > > >
> > > > @@ -383,6 +395,10 @@ static void
> > > acpi_bus_osc_negotiate_platform_control(void)
> > > > capbuf_ret[OSC_SUPPORT_DWORD] &
> > > OSC_SB_NATIVE_USB4_SUPPORT;
> > > > osc_cpc_flexible_adr_space_confirmed =
> > > > capbuf_ret[OSC_SUPPORT_DWORD] &
> > > OSC_SB_CPC_FLEXIBLE_ADR_SPACE;
> > > > + osc_sb_hotplug_enabled_support_acked =
> > > > + capbuf_ret[OSC_SUPPORT_DWORD] &
> > > OSC_SB_HOTPLUG_ENABLED_SUPPORT;
> > > > + osc_sb_hotplug_present_support_acked =
> > > > + capbuf_ret[OSC_SUPPORT_DWORD] &
> > > OSC_SB_HOTPLUG_PRESENT_SUPPORT;
> > > > }
> > > >
> > > > kfree(context.ret.pointer);
> > > > diff --git a/include/linux/acpi.h b/include/linux/acpi.h index
> > > > 00be66683505..c572abac803c 100644
> > > > --- a/include/linux/acpi.h
> > > > +++ b/include/linux/acpi.h
> > > > @@ -559,12 +559,16 @@ acpi_status acpi_run_osc(acpi_handle handle,
> > > struct acpi_osc_context *context);
> > > > #define OSC_SB_NATIVE_USB4_SUPPORT 0x00040000
> > > > #define OSC_SB_PRM_SUPPORT 0x00200000
> > > > #define OSC_SB_FFH_OPR_SUPPORT 0x00400000
> > > > +#define OSC_SB_HOTPLUG_ENABLED_SUPPORT 0x00800000
> > > > +#define OSC_SB_HOTPLUG_PRESENT_SUPPORT 0x01000000
> > > >
> > > > extern bool osc_sb_apei_support_acked; extern bool
> > > > osc_pc_lpi_support_confirmed; extern bool
> > > > osc_sb_native_usb4_support_confirmed;
> > > > extern bool osc_sb_cppc2_support_acked; extern bool
> > > > osc_cpc_flexible_adr_space_confirmed;
> > > > +extern bool osc_sb_hotplug_enabled_support_acked;
> > > > +extern bool osc_sb_hotplug_present_support_acked;
> > > >
> > > > /* USB4 Capabilities */
> > > > #define OSC_USB_USB3_TUNNELING 0x00000001
> >