linux-kernel - Re: [PATCH v14 03/13] x86/sev: Add Secure TSC support for SNP guests

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Message-ID: <3782c833-94a0-4e41-9f40-8505a2681393@intel.com>
Date: Tue, 29 Oct 2024 17:19:29 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: "Nikunj A. Dadhania" <nikunj@....com>, linux-kernel@...r.kernel.org,
 thomas.lendacky@....com, bp@...en8.de, x86@...nel.org, kvm@...r.kernel.org
Cc: mingo@...hat.com, tglx@...utronix.de, dave.hansen@...ux.intel.com,
 pgonda@...gle.com, seanjc@...gle.com, pbonzini@...hat.com
Subject: Re: [PATCH v14 03/13] x86/sev: Add Secure TSC support for SNP guests

On 10/29/2024 4:46 PM, Nikunj A. Dadhania wrote:
> 
> 
> On 10/29/2024 2:11 PM, Xiaoyao Li wrote:
>> On 10/28/2024 1:34 PM, Nikunj A Dadhania wrote:
>>> Add support for Secure TSC in SNP-enabled guests. Secure TSC allows guests
>>> to securely use RDTSC/RDTSCP instructions, ensuring that the parameters
>>> used cannot be altered by the hypervisor once the guest is launched.
>>>
>>> Secure TSC-enabled guests need to query TSC information from the AMD
>>> Security Processor. This communication channel is encrypted between the AMD
>>> Security Processor and the guest, with the hypervisor acting merely as a
>>> conduit to deliver the guest messages to the AMD Security Processor. Each
>>> message is protected with AEAD (AES-256 GCM). Use a minimal AES GCM library
>>> to encrypt and decrypt SNP guest messages for communication with the PSP.
>>>
>>> Use mem_encrypt_init() to fetch SNP TSC information from the AMD Security
>>> Processor and initialize snp_tsc_scale and snp_tsc_offset.
>>
>> Why do it inside mem_encrypt_init()?
> 
> It was discussed here: https://lore.kernel.org/lkml/20240422132058.GBZiZkOqU0zFviMzoC@fat_crate.local/

IMHO, it's a bad starter. As more and more SNP features will be enabled 
in the future, a SNP init function like tdx_early_init() would be a good 
place for all SNP guest stuff.

Just my 2 cents.

> Regards
> Nikunj