> -----Original Message----- > From: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx> > Sent: Tuesday, January 2, 2024 3:17 PM > To: Jose Marinho <Jose.Marinho@xxxxxxx> > Cc: Russell King (Oracle) <rmk+kernel@xxxxxxxxxxxxxxx>; linux- > pm@xxxxxxxxxxxxxxx; loongarch@xxxxxxxxxxxxxxx; linux-acpi@xxxxxxxxxxxxxxx; > linux-arch@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-arm- > kernel@xxxxxxxxxxxxxxxxxxx; linux-riscv@xxxxxxxxxxxxxxxxxxx; > kvmarm@xxxxxxxxxxxxxxx; x86@xxxxxxxxxx; acpica- > devel@xxxxxxxxxxxxxxxxxxxxxxxxx; linux-csky@xxxxxxxxxxxxxxx; linux- > doc@xxxxxxxxxxxxxxx; linux-ia64@xxxxxxxxxxxxxxx; linux-parisc@xxxxxxxxxxxxxxx; > Salil Mehta <salil.mehta@xxxxxxxxxx>; Jean-Philippe Brucker <jean- > philippe@xxxxxxxxxx>; Jianyong Wu <Jianyong.Wu@xxxxxxx>; Justin He > <Justin.He@xxxxxxx>; James Morse <James.Morse@xxxxxxx>; Samer El-Haj- > Mahmoud <Samer.El-Haj-Mahmoud@xxxxxxx>; nd <nd@xxxxxxx>; Kangkang > Shen <kangkang.shen@xxxxxxxxxxxxx> > 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@xxxxxxx> wrote: > > > Hi Jonathan, > > > > > -----Original Message----- > > > From: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx> > > > Sent: Friday, December 15, 2023 5:12 PM > > > To: Russell King (Oracle) <rmk+kernel@xxxxxxxxxxxxxxx> > > > Cc: linux-pm@xxxxxxxxxxxxxxx; loongarch@xxxxxxxxxxxxxxx; linux- > > > acpi@xxxxxxxxxxxxxxx; linux-arch@xxxxxxxxxxxxxxx; linux- > > > kernel@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux- > > > riscv@xxxxxxxxxxxxxxxxxxx; kvmarm@xxxxxxxxxxxxxxx; x86@xxxxxxxxxx; > > > acpica- devel@xxxxxxxxxxxxxxxxxxxxxxxxx; linux-csky@xxxxxxxxxxxxxxx; > > > linux- doc@xxxxxxxxxxxxxxx; linux-ia64@xxxxxxxxxxxxxxx; linux- > > > parisc@xxxxxxxxxxxxxxx; Salil Mehta <salil.mehta@xxxxxxxxxx>; > > > Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>; Jianyong Wu > > > <Jianyong.Wu@xxxxxxx>; Justin He <Justin.He@xxxxxxx>; James Morse > > > <James.Morse@xxxxxxx>; Jose Marinho <Jose.Marinho@xxxxxxx>; Samer > > > El-Haj-Mahmoud <Samer.El- Haj-Mahmoud@xxxxxxx> > > > 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@xxxxxxxxxxxxxxx> wrote: > > > > > > > From: James Morse <james.morse@xxxxxxx> > > > > > > > > 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@xxxxxxx> > > > > Tested-by: Miguel Luis <miguel.luis@xxxxxxxxxx> > > > > Tested-by: Vishnu Pajjuri <vishnu@xxxxxxxxxxxxxxxxxxxxxx> > > > > Tested-by: Jianyong Wu <jianyong.wu@xxxxxxx> > > > > > > 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@xxxxxxxxxxxxxx) , 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@xxxxxxxxxx > > > > > > > > > > > > > --- > > > > 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 > >
