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Date: Mon, 10 May 2021 18:55:14 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: "Kuppuswamy, Sathyanarayanan"
<sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc: Rafael J Wysocki <rjw@...ysocki.net>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H . Peter Anvin" <hpa@...or.com>,
Peter Zijlstra <peterz@...radead.org>,
Len Brown <lenb@...nel.org>,
Robert Moore <robert.moore@...el.com>,
Erik Kaneda <erik.kaneda@...el.com>,
ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
"open list:ACPI COMPONENT ARCHITECTURE (ACPICA)" <devel@...ica.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
"the arch/x86 maintainers" <x86@...nel.org>,
Sean Christopherson <sean.j.christopherson@...el.com>,
Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH v3 3/3] x86/acpi, x86/boot: Add multiprocessor wake-up support
On Mon, May 10, 2021 at 6:33 PM Kuppuswamy, Sathyanarayanan
<sathyanarayanan.kuppuswamy@...ux.intel.com> wrote:
>
> Hi Rafael/Thomas,
>
> On 4/25/21 7:39 PM, Kuppuswamy Sathyanarayanan wrote:
> > As per ACPI specification r6.4, sec 5.2.12.19, a new sub
> > structure – multiprocessor wake-up structure - is added to the
> > ACPI Multiple APIC Description Table (MADT) to describe the
> > information of the mailbox. If a platform firmware produces the
> > multiprocessor wake-up structure, then OS may use this new
> > mailbox-based mechanism to wake up the APs.
> >
> > Add ACPI MADT wake table parsing support for x86 platform and if
> > MADT wake table is present, update apic->wakeup_secondary_cpu with
> > new API which uses MADT wake mailbox to wake-up CPU.
>
> Gentle ping. Any comments on this patch? I think I have addressed
> the concerns raised by you in previous version.
>
> >
> > Co-developed-by: Sean Christopherson <sean.j.christopherson@...el.com>
> > Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> > Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> > Reviewed-by: Andi Kleen <ak@...ux.intel.com>
> > ---
> > arch/x86/include/asm/apic.h | 3 ++
> > arch/x86/kernel/acpi/boot.c | 79 +++++++++++++++++++++++++++++++++++++
> > arch/x86/kernel/apic/apic.c | 8 ++++
> > 3 files changed, 90 insertions(+)
> >
> > diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
> > index 412b51e059c8..3e94e1f402ea 100644
> > --- a/arch/x86/include/asm/apic.h
> > +++ b/arch/x86/include/asm/apic.h
> > @@ -487,6 +487,9 @@ static inline unsigned int read_apic_id(void)
> > return apic->get_apic_id(reg);
> > }
> >
> > +typedef int (*wakeup_cpu_handler)(int apicid, unsigned long start_eip);
> > +extern void acpi_wake_cpu_handler_update(wakeup_cpu_handler handler);
> > +
> > extern int default_apic_id_valid(u32 apicid);
> > extern int default_acpi_madt_oem_check(char *, char *);
> > extern void default_setup_apic_routing(void);
> > diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
> > index 14cd3186dc77..fce2aa7d718f 100644
> > --- a/arch/x86/kernel/acpi/boot.c
> > +++ b/arch/x86/kernel/acpi/boot.c
> > @@ -65,6 +65,9 @@ int acpi_fix_pin2_polarity __initdata;
> > static u64 acpi_lapic_addr __initdata = APIC_DEFAULT_PHYS_BASE;
> > #endif
> >
> > +static struct acpi_madt_multiproc_wakeup_mailbox *acpi_mp_wake_mailbox;
> > +static u64 acpi_mp_wake_mailbox_paddr;
> > +
> > #ifdef CONFIG_X86_IO_APIC
> > /*
> > * Locks related to IOAPIC hotplug
> > @@ -329,6 +332,52 @@ acpi_parse_lapic_nmi(union acpi_subtable_headers * header, const unsigned long e
> > return 0;
> > }
> >
> > +static void acpi_mp_wake_mailbox_init(void)
> > +{
> > + if (acpi_mp_wake_mailbox)
> > + return;
> > +
> > + acpi_mp_wake_mailbox = memremap(acpi_mp_wake_mailbox_paddr,
> > + sizeof(*acpi_mp_wake_mailbox), MEMREMAP_WB);
> > +}
> > +
> > +static int acpi_wakeup_cpu(int apicid, unsigned long start_ip)
> > +{
> > + u8 timeout = 0xFF;
> > +
> > + acpi_mp_wake_mailbox_init();
> > +
> > + if (!acpi_mp_wake_mailbox)
> > + return -EINVAL;
> > +
> > + /*
> > + * Mailbox memory is shared between firmware and OS. Firmware will
> > + * listen on mailbox command address, and once it receives the wakeup
> > + * command, CPU associated with the given apicid will be booted. So,
> > + * the value of apic_id and wakeup_vector has to be set before updating
> > + * the wakeup command. So use WRITE_ONCE to let the compiler know about
> > + * it and preserve the order of writes.
> > + */
> > + WRITE_ONCE(acpi_mp_wake_mailbox->apic_id, apicid);
> > + WRITE_ONCE(acpi_mp_wake_mailbox->wakeup_vector, start_ip);
> > + WRITE_ONCE(acpi_mp_wake_mailbox->command, ACPI_MP_WAKE_COMMAND_WAKEUP);
> > +
> > + /*
> > + * After writing wakeup command, wait for maximum timeout of 0xFF
> > + * for firmware to reset the command address back zero to indicate
> > + * the successful reception of command.
> > + * NOTE: 255 as timeout value is decided based on our experiments.
> > + *
> > + * XXX: Change the timeout once ACPI specification comes up with
> > + * standard maximum timeout value.
> > + */
> > + while (READ_ONCE(acpi_mp_wake_mailbox->command) && timeout--)
> > + cpu_relax();
> > +
> > + /* If timedout, return error */
> > + return timeout ? 0 : -EIO;
I'm not sure how my comment regarding the fact that for a given CPU
this function is only usable once has been addressed.
While it may not be a practical concern in the use case that you are
after (TDX), this is a generic mechanism and it needs to cover other
possible usage scenarios.
> > +}
> > +
> > #endif /*CONFIG_X86_LOCAL_APIC */
> >
> > #ifdef CONFIG_X86_IO_APIC
> > @@ -1086,6 +1135,30 @@ static int __init acpi_parse_madt_lapic_entries(void)
> > }
> > return 0;
> > }
> > +
> > +static int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
> > + const unsigned long end)
> > +{
> > + struct acpi_madt_multiproc_wakeup *mp_wake;
> > +
> > + if (acpi_mp_wake_mailbox)
> > + return -EINVAL;
> > +
> > + if (!IS_ENABLED(CONFIG_SMP))
> > + return -ENODEV;
> > +
> > + mp_wake = (struct acpi_madt_multiproc_wakeup *) header;
> > + if (BAD_MADT_ENTRY(mp_wake, end))
> > + return -EINVAL;
> > +
> > + acpi_table_print_madt_entry(&header->common);
> > +
> > + acpi_mp_wake_mailbox_paddr = mp_wake->base_address;
> > +
> > + acpi_wake_cpu_handler_update(acpi_wakeup_cpu);
> > +
> > + return 0;
> > +}
> > #endif /* CONFIG_X86_LOCAL_APIC */
> >
> > #ifdef CONFIG_X86_IO_APIC
> > @@ -1284,6 +1357,12 @@ static void __init acpi_process_madt(void)
> >
> > smp_found_config = 1;
> > }
> > +
> > + /*
> > + * Parse MADT MP Wake entry.
> > + */
> > + acpi_table_parse_madt(ACPI_MADT_TYPE_MULTIPROC_WAKEUP,
> > + acpi_parse_mp_wake, 1);
> > }
> > if (error == -EINVAL) {
> > /*
> > diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> > index 4f26700f314d..f1b90a4b89e8 100644
> > --- a/arch/x86/kernel/apic/apic.c
> > +++ b/arch/x86/kernel/apic/apic.c
> > @@ -2554,6 +2554,14 @@ u32 x86_msi_msg_get_destid(struct msi_msg *msg, bool extid)
> > }
> > EXPORT_SYMBOL_GPL(x86_msi_msg_get_destid);
> >
> > +void __init acpi_wake_cpu_handler_update(wakeup_cpu_handler handler)
> > +{
> > + struct apic **drv;
> > +
> > + for (drv = __apicdrivers; drv < __apicdrivers_end; drv++)
> > + (*drv)->wakeup_secondary_cpu = handler;
> > +}
> > +
> > /*
> > * Override the generic EOI implementation with an optimized version.
> > * Only called during early boot when only one CPU is active and with
> >
>
> --
> Sathyanarayanan Kuppuswamy
> Linux Kernel Developer
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