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Message-ID: <1185a15a1b4238092813a8134d86c93d73d84403.camel@intel.com>
Date: Tue, 24 Oct 2023 10:14:51 +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>,
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CC: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
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"Nakajima, Jun" <jun.nakajima@...el.com>,
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"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
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"linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>
Subject: Re: [PATCHv2 11/13] x86/acpi: Do not attempt to bring up secondary
CPUs in kexec case
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@...ux.intel.com>
Reviewed-by: Kai Huang <kai.huang@...el.com>
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