linux-kernel - Re: [PATCHv6 00/16] x86/tdx: Add kexec support

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Message-ID: <5d91fc11-0b3b-40f0-872d-abdbb4038f76@suse.com>
Date: Wed, 31 Jan 2024 14:58:30 +0200
From: Nikolay Borisov <nik.borisov@...e.com>
To: Baoquan He <bhe@...hat.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>,
 "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org, "Rafael J. Wysocki" <rafael@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>,
 Adrian Hunter <adrian.hunter@...el.com>,
 Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>,
 Elena Reshetova <elena.reshetova@...el.com>,
 Jun Nakajima <jun.nakajima@...el.com>,
 Rick Edgecombe <rick.p.edgecombe@...el.com>,
 Tom Lendacky <thomas.lendacky@....com>, "Kalra, Ashish"
 <ashish.kalra@....com>, Sean Christopherson <seanjc@...gle.com>,
 "Huang, Kai" <kai.huang@...el.com>, kexec@...ts.infradead.org,
 linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv6 00/16] x86/tdx: Add kexec support

On 31.01.24 г. 14:47 ч., Baoquan He wrote:
> On 01/31/24 at 09:31am, Nikolay Borisov wrote:
>>
>>
>> On 30.01.24 г. 15:43 ч., Paolo Bonzini wrote:
>>> On 1/24/24 13:55, Kirill A. Shutemov wrote:
>>>> The patchset adds bits and pieces to get kexec (and crashkernel) work on
>>>> TDX guest.
>>>>
>>>> The last patch implements CPU offlining according to the approved ACPI
>>>> spec change poposal[1]. It unlocks kexec with all CPUs visible in
>>>> the target
>>>> kernel. It requires BIOS-side enabling. If it missing we fallback to
>>>> booting
>>>> 2nd kernel with single CPU.
>>>>
>>>> Please review. I would be glad for any feedback.
>>>
>>> Hi Kirill,
>>>
>>> I have a very basic question: is there a reason why this series does not
>>> revert commit cb8eb06d50fc, "x86/virt/tdx: Disable TDX host support when
>>> kexec is enabled"?
>>
>> While on the topic, Paolo do you think it's  better to have a runtime
>> disable of kexec rather than at compile time:
>>
>> [RFC PATCH] x86/virt/tdx: Disable KEXEC in the presence of TDX
>>
>> 20240118160118.1899299-1-nik.borisov@...e.com
> 
> Runtime disabling kexec looks better than at cmpile time, esp for
> distros. While from above patch, making using of kexec_load_disabled to
> achive the runtime disabling may not be so good. Because we have a front
> door to enable it through:
> 
> /proc/sys/kernel/kexec_load_disabled

AFAIU it can't be enabled via this sysctl because the handler for it 
expects only 1 to be written to it:

      2                 .proc_handler   = proc_dointvec_minmax, 

      1                 .extra1         = SYSCTL_ONE, 

   994                  .extra2         = SYSCTL_ONE,

> 
> If there's a flag or status to check if TDX host is enabled, and does
> the checking in kexec_load_permitted(), that could be better. Anyway, I
> saw Huang, Kai has posted the tdx host support patchset.
> 
>>
>> I'm trying to get traction for this patch.
>>
>>
>>>
>>> Thanks,
>>>
>>> Paolo
>>>
>>>
>>
>