Re: [PATCHv2 01/13] x86/acpi: Extract ACPI MADT wakeup code into a separate file

[Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>]

On 10/20/2023 8:12 AM, Kirill A. Shutemov wrote:
> In order to prepare for the expansion of support for the ACPI MADT
> wakeup method, move the relevant code into a separate file.
> 
> Introduce a new configuration option to clearly indicate dependencies
> without the use of ifdefs.
> 
> There have been no functional changes.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---

Looks good to me.

Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.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 | 81 ++++++++++++++++++++++++++++
>  5 files changed, 100 insertions(+), 90 deletions(-)
>  create mode 100644 arch/x86/kernel/acpi/madt_wakeup.c
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 799102f4d909..9957a73bb386 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
>  
> diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
> index 2a0ea38955df..111bd226ad99 100644
> --- a/arch/x86/kernel/acpi/boot.c
> +++ b/arch/x86/kernel/acpi/boot.c
> @@ -66,13 +66,6 @@ static u64 acpi_lapic_addr __initdata = APIC_DEFAULT_PHYS_BASE;
>  static bool acpi_support_online_capable;
>  #endif
>  
> -#ifdef CONFIG_X86_64
> -/* 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;
> -#endif
> -
>  #ifdef CONFIG_X86_IO_APIC
>  /*
>   * Locks related to IOAPIC hotplug
> @@ -357,60 +350,6 @@ acpi_parse_lapic_nmi(union acpi_subtable_headers * header, const unsigned long e
>  
>  	return 0;
>  }
> -
> -#ifdef CONFIG_X86_64
> -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;
> -}
> -#endif /* CONFIG_X86_64 */
>  #endif /* CONFIG_X86_LOCAL_APIC */
>  
>  #ifdef CONFIG_X86_IO_APIC
> @@ -1160,29 +1099,6 @@ static int __init acpi_parse_madt_lapic_entries(void)
>  	}
>  	return 0;
>  }
> -
> -#ifdef CONFIG_X86_64
> -static 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;
> -
> -	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;
> -}
> -#endif				/* CONFIG_X86_64 */
>  #endif				/* CONFIG_X86_LOCAL_APIC */
>  
>  #ifdef	CONFIG_X86_IO_APIC
> @@ -1379,7 +1295,7 @@ static void __init acpi_process_madt(void)
>  				smp_found_config = 1;
>  			}
>  
> -#ifdef CONFIG_X86_64
> +#ifdef CONFIG_X86_ACPI_MADT_WAKEUP
>  			/*
>  			 * Parse MADT MP Wake entry.
>  			 */
> diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
> new file mode 100644
> index 000000000000..58cdfc0b6c0a
> --- /dev/null
> +++ b/arch/x86/kernel/acpi/madt_wakeup.c
> @@ -0,0 +1,81 @@
> +#include <linux/acpi.h>
> +#include <linux/io.h>
> +#include <asm/apic.h>
> +#include <asm/barrier.h>
> +#include <asm/processor.h>
> +
> +/* 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;
> +
> +	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;
> +}

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer