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Message-ID: <c8ea05e6-58e5-4371-88fe-cde3f09dd530@linux.intel.com>
Date: Mon, 30 Jun 2025 15:09:19 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: "Huang, Kai" <kai.huang@...el.com>
Cc: "Hansen, Dave" <dave.hansen@...el.com>,
"Edgecombe, Rick P" <rick.p.edgecombe@...el.com>, "bp@...en8.de"
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Subject: Re: [PATCH v3 1/6] x86/sme: Use percpu boolean to control wbinvd
during kexec
On 6/27/2025 8:30 AM, Huang, Kai wrote:
[...]
>
> And I am not 100% sure whether this issue exists, since allowing CPU hotplug
> during kexec doesn't seem reasonable to me at least on x86, despite it is
> indeed enabled kernel_kexec() common code:
>
> /*
> * migrate_to_reboot_cpu() disables CPU hotplug assuming that
> * no further code needs to use CPU hotplug (which is true in
> * the reboot case). However, the kexec path depends on using
> * CPU hotplug again; so re-enable it here.
> */
> cpu_hotplug_enable();
> pr_notice("Starting new kernel\n");
> machine_shutdown();
>
> I tried to git blame to find clue but failed since the history is lost
> during file move/renaming etc. I suspect it is for other ARCHs.
>
Had a check in git history, it's related to powerpc kexec code.
First, commit e8e5c2155b00 ("powerpc/kexec: Fix orphaned offline CPUs across kexec")
add the code to online each present CPU.
Later, commit011e4b02f1da (" powerpc, kexec: Fix "Processor X is stuck" issue
during kexec from ST mode") add the code in the common code kernel_kexec() to
enable hotplug to fix the stuck issue.
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