linux-kernel - Re: [PATCH v3 1/6] x86/sme: Use percpu boolean to control wbinvd during kexec

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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"
 <bp@...en8.de>, "peterz@...radead.org" <peterz@...radead.org>,
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 "sagis@...gle.com" <sagis@...gle.com>,
 "Chatre, Reinette" <reinette.chatre@...el.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
 "Williams, Dan J" <dan.j.williams@...el.com>,
 "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
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 "Yamahata, Isaku" <isaku.yamahata@...el.com>,
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 "nik.borisov@...e.com" <nik.borisov@...e.com>
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.