linux-kernel - Re: [PATCH v7 3/6] x86/topology: Disable CPU online/offline control for TDX guest

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Date:   Sun, 17 Oct 2021 12:28:39 -0700
From:   Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, Paolo Bonzini <pbonzini@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 3/6] x86/topology: Disable CPU online/offline control
 for TDX guest


On 10/17/21 12:23 PM, Thomas Gleixner wrote:
> Seriously? This lets the unplug start, which starts to kick off tasks
> from the CPU just to make it fail a few steps later?
>
> The obvious place to prevent this is the CPU hotplug code itself, right?
>
> Thanks,
>
>          tglx
> ---
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 192e43a87407..c544eb6c79d3 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -1178,6 +1178,8 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
>   
>   static int cpu_down_maps_locked(unsigned int cpu, enum cpuhp_state target)
>   {
> +	if (cc_platform_has(CC_HOTPLUG_DISABLED))
> +		return -ENOTSUPP;
>   	if (cpu_hotplug_disabled)
>   		return -EBUSY;
>   	return _cpu_down(cpu, 0, target);

Makes sense. I will use it in next version.

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer