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Message-ID: <20231006115937.js5zkqlbqyv3venr@box.shutemov.name>
Date: Fri, 6 Oct 2023 14:59:37 +0300
From: "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>
To: "Huang, Kai" <kai.huang@...el.com>
Cc: "tglx@...utronix.de" <tglx@...utronix.de>,
"mingo@...hat.com" <mingo@...hat.com>,
"x86@...nel.org" <x86@...nel.org>, "bp@...en8.de" <bp@...en8.de>,
"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
"Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
"Reshetova, Elena" <elena.reshetova@...el.com>,
"Nakajima, Jun" <jun.nakajima@...el.com>,
"rafael@...nel.org" <rafael@...nel.org>,
"peterz@...radead.org" <peterz@...radead.org>,
"sathyanarayanan.kuppuswamy@...ux.intel.com"
<sathyanarayanan.kuppuswamy@...ux.intel.com>,
"Hunter, Adrian" <adrian.hunter@...el.com>,
"thomas.lendacky@....com" <thomas.lendacky@....com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
"linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>
Subject: Re: [PATCH 01/13] x86/acpi: Extract ACPI MADT wakeup code into a
separate file
On Fri, Oct 06, 2023 at 10:22:54AM +0000, Huang, Kai wrote:
> On Thu, 2023-10-05 at 16:13 +0300, Kirill A. Shutemov wrote:
> > In order to prepare for the expansion of support for the ACPI MADT
> > wakeup method, the relevant code has been moved into a separate file.
> > A new configuration option has been introduced to clearly indicate
> > dependencies without the use of ifdefs.
>
> Use imperative mood?
>
> - Move the relevant code into ...
> - Introduce a new configuration option to ...
Okay.
> > There have been no functional changes.
> >
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> > ---
> > arch/x86/Kconfig | 7 +++
> > arch/x86/include/asm/acpi.h | 5 ++
> > arch/x86/kernel/acpi/Makefile | 11 ++--
> > arch/x86/kernel/acpi/boot.c | 86 +-----------------------------
> > arch/x86/kernel/acpi/madt_wakeup.c | 80 +++++++++++++++++++++++++++
> > 5 files changed, 99 insertions(+), 90 deletions(-)
> > create mode 100644 arch/x86/kernel/acpi/madt_wakeup.c
> >
> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > index 3154dbc49cf5..7368d254d01f 100644
> > --- a/arch/x86/Kconfig
> > +++ b/arch/x86/Kconfig
> > @@ -1108,6 +1108,13 @@ config X86_LOCAL_APIC
> > depends on X86_64 || SMP || X86_32_NON_STANDARD || X86_UP_APIC || PCI_MSI
> > select IRQ_DOMAIN_HIERARCHY
> >
> > +config X86_ACPI_MADT_WAKEUP
> > + def_bool y
> > + depends on X86_64
> > + depends on ACPI
> > + depends on SMP
> > + depends on X86_LOCAL_APIC
> > +
> > config X86_IO_APIC
> > def_bool y
> > depends on X86_LOCAL_APIC || X86_UP_IOAPIC
> > diff --git a/arch/x86/include/asm/acpi.h b/arch/x86/include/asm/acpi.h
> > index c8a7fc23f63c..b536b5a6a57b 100644
> > --- a/arch/x86/include/asm/acpi.h
> > +++ b/arch/x86/include/asm/acpi.h
> > @@ -73,6 +73,11 @@ static inline bool acpi_skip_set_wakeup_address(void)
> >
> > #define acpi_skip_set_wakeup_address acpi_skip_set_wakeup_address
> >
> > +union acpi_subtable_headers;
> > +
> > +int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
> > + const unsigned long end);
> > +
> > /*
> > * Check if the CPU can handle C2 and deeper
> > */
> > diff --git a/arch/x86/kernel/acpi/Makefile b/arch/x86/kernel/acpi/Makefile
> > index fc17b3f136fe..8c7329c88a75 100644
> > --- a/arch/x86/kernel/acpi/Makefile
> > +++ b/arch/x86/kernel/acpi/Makefile
> > @@ -1,11 +1,12 @@
> > # SPDX-License-Identifier: GPL-2.0
> >
> > -obj-$(CONFIG_ACPI) += boot.o
> > -obj-$(CONFIG_ACPI_SLEEP) += sleep.o wakeup_$(BITS).o
> > -obj-$(CONFIG_ACPI_APEI) += apei.o
> > -obj-$(CONFIG_ACPI_CPPC_LIB) += cppc.o
> > +obj-$(CONFIG_ACPI) += boot.o
> > +obj-$(CONFIG_ACPI_SLEEP) += sleep.o wakeup_$(BITS).o
> > +obj-$(CONFIG_ACPI_APEI) += apei.o
> > +obj-$(CONFIG_ACPI_CPPC_LIB) += cppc.o
> > +obj-$(CONFIG_X86_ACPI_MADT_WAKEUP) += madt_wakeup.o
> >
> > ifneq ($(CONFIG_ACPI_PROCESSOR),)
> > -obj-y += cstate.o
> > +obj-y += cstate.o
> > endif
>
> unintended code change?
No. It keeps += aligned as they are before the patch.
>
> [...]
>
> >
> > diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
> > new file mode 100644
> > index 000000000000..1b9747bfd5b9
> > --- /dev/null
> > +++ b/arch/x86/kernel/acpi/madt_wakeup.c
> > @@ -0,0 +1,80 @@
> > +#include <linux/acpi.h>
> > +#include <asm/apic.h>
>
> Functions like memremap(), smp_store_release() and cpu_relax() are used in this
> file. Should we explicitly include the relevant headers?
Okay, will do.
> > +
> > +/* Physical address of the Multiprocessor Wakeup Structure mailbox */
> > +static u64 acpi_mp_wake_mailbox_paddr;
> > +/* Virtual address of the Multiprocessor Wakeup Structure mailbox */
> > +static struct acpi_madt_multiproc_wakeup_mailbox *acpi_mp_wake_mailbox;
> > +
> > +static int acpi_wakeup_cpu(int apicid, unsigned long start_ip)
> > +{
> > + /*
> > + * Remap mailbox memory only for the first call to acpi_wakeup_cpu().
> > + *
> > + * Wakeup of secondary CPUs is fully serialized in the core code.
> > + * No need to protect acpi_mp_wake_mailbox from concurrent accesses.
> > + */
> > + if (!acpi_mp_wake_mailbox) {
> > + acpi_mp_wake_mailbox = memremap(acpi_mp_wake_mailbox_paddr,
> > + sizeof(*acpi_mp_wake_mailbox),
> > + MEMREMAP_WB);
> > + }
> > +
> > + /*
> > + * Mailbox memory is shared between the firmware and OS. Firmware will
> > + * listen on mailbox command address, and once it receives the wakeup
> > + * command, the CPU associated with the given apicid will be booted.
> > + *
> > + * The value of 'apic_id' and 'wakeup_vector' must be visible to the
> > + * firmware before the wakeup command is visible. smp_store_release()
> > + * ensures ordering and visibility.
> > + */
> > + acpi_mp_wake_mailbox->apic_id = apicid;
> > + acpi_mp_wake_mailbox->wakeup_vector = start_ip;
> > + smp_store_release(&acpi_mp_wake_mailbox->command,
> > + ACPI_MP_WAKE_COMMAND_WAKEUP);
> > +
> > + /*
> > + * Wait for the CPU to wake up.
> > + *
> > + * The CPU being woken up is essentially in a spin loop waiting to be
> > + * woken up. It should not take long for it wake up and acknowledge by
> > + * zeroing out ->command.
> > + *
> > + * ACPI specification doesn't provide any guidance on how long kernel
> > + * has to wait for a wake up acknowledgement. It also doesn't provide
> > + * a way to cancel a wake up request if it takes too long.
> > + *
> > + * In TDX environment, the VMM has control over how long it takes to
> > + * wake up secondary. It can postpone scheduling secondary vCPU
> > + * indefinitely. Giving up on wake up request and reporting error opens
> > + * possible attack vector for VMM: it can wake up a secondary CPU when
> > + * kernel doesn't expect it. Wait until positive result of the wake up
> > + * request.
> > + */
> > + while (READ_ONCE(acpi_mp_wake_mailbox->command))
> > + cpu_relax();
> > +
> > + return 0;
> > +}
> > +
> > +int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
> > + const unsigned long end)
> > +{
> > + struct acpi_madt_multiproc_wakeup *mp_wake;
> > +
> > + if (!IS_ENABLED(CONFIG_SMP))
> > + return -ENODEV;
>
> Now you have made X86_ACPI_MADT_WAKEUP depend on SMP, and this file will only be
> compiled when X86_ACPI_MADT_WAKEUP is turned on. IIUC this essentially means
> IS_ENABLED(CONFIG_SMP) will always report true?
Good catch. I didn't have 'depends SMP' initially, but it triggered build
issue, so I added it, but forgot to drop IS_ENABLED().
> > +
> > + 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;
> > +
> > + apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
> > +
> > + return 0;
> > +}
>
--
Kiryl Shutsemau / Kirill A. Shutemov
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