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Message-ID: <e11888bc9775a8083b72cce8c58ee71b39d0e17f.camel@intel.com>
Date: Fri, 6 Oct 2023 10:22:54 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
"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>
CC: "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 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 ...
>
> 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?
[...]
>
> 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?
> +
> +/* 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?
> +
> + 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;
> +}
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