linux-kernel - Re: [PATCH v2 2/5] x86/kexec: do unconditional WBINVD in relocate

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Date: Wed, 20 Mar 2024 16:06:50 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: "Huang, Kai" <kai.huang@...el.com>,
 "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org, dave.hansen@...el.com,
 bp@...en8.de, tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
 luto@...nel.org, peterz@...radead.org, rick.p.edgecombe@...el.com,
 ashish.kalra@....com, chao.gao@...el.com, bhe@...hat.com,
 nik.borisov@...e.com, pbonzini@...hat.com, seanjc@...gle.com
Subject: Re: [PATCH v2 2/5] x86/kexec: do unconditional WBINVD in
 relocate_kernel()

On 3/20/24 15:48, Huang, Kai wrote:
> 
>>> Hi Tom,
>>>
>>> I am not aware of kexec() support status for SEV-ES/SEV-SNP guests. 
>>> Does patch 1 break them?
>>
>> SNP guests can kexec with some patches that are currently in process 
>> around shared to private memory conversions. ES guests can only kexec 
>> with a single vCPU. There was a recent patch series to add support for 
>> multiple vCPUs.
>>
>> Patch #1 doesn't break either ES or SNP because we still have an IDT and 
>> traditional kernel addressing in place, so the #VC can be handled.
> 
> How about plain SEV guest?

A plain SEV guest is fine, since WBINVD is intercepted and would just exit 
to the hypervisor (#VC doesn't happen with plain SEV).

Thanks,
Tom

> 
>>
>> Whereas patch #2 has switched to identity mapping and removed the IDT, 
>> so a #VC causes a triple fault.
> 
> That makes sense.  Thanks.
> 
> Hi Kirill,
> 
> Does TDX guest have similar behaviour -- that WBINVD in stop_this_cpu() 
> can be handled although it causes #VE, while WBINVD in relocate_kernel() 
> will just triple fault the guest?