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// SPDX-License-Identifier: GPL-2.0-or-later
#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(u32 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 acknowledgment. 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;
}
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