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SubjectRe: [PATCHv2 11/13] x86/acpi: Do not attempt to bring up secondary CPUs in kexec case
Date
On Fri, 2023-10-20 at 18:12 +0300, Kirill A. Shutemov wrote:
> ACPI MADT doesn't allow to offline CPU after it got woke up. It limits
> kexec: the second kernel won't be able to use more than one CPU.
>
> Now acpi_mp_wake_mailbox_paddr already has the mailbox address.
> The acpi_wakeup_cpu() will use it to bring up secondary cpus.
>
> Zero out mailbox address in the ACPI MADT wakeup structure to indicate
> that the mailbox is not usable. This prevents the kexec()-ed kernel
> from reading a vaild mailbox, which in turn makes the kexec()-ed kernel
> only be able to use the boot CPU.
>
> This is Linux-specific protocol and not reflected in ACPI spec.
>
> Booting the second kernel with signle CPU is enough to cover the most
> common case for kexec -- kdump.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

Reviewed-by: Kai Huang <kai.huang@intel.com>

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