linux-kernel - Re: [PATCH v1 04/26] x86/sev: Add the host SEV-SNP initialization support

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Message-ID: <b6f00233-0cbf-4d9a-aa8b-babc8a9ca696@linux.microsoft.com>
Date: Wed, 14 Feb 2024 17:56:56 +0100
From: Jeremi Piotrowski <jpiotrowski@...ux.microsoft.com>
To: Borislav Petkov <bp@...en8.de>, Michael Roth <michael.roth@....com>
Cc: x86@...nel.org, kvm@...r.kernel.org, linux-coco@...ts.linux.dev,
 linux-mm@...ck.org, linux-crypto@...r.kernel.org,
 linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
 jroedel@...e.de, thomas.lendacky@....com, hpa@...or.com, ardb@...nel.org,
 pbonzini@...hat.com, seanjc@...gle.com, vkuznets@...hat.com,
 jmattson@...gle.com, luto@...nel.org, dave.hansen@...ux.intel.com,
 slp@...hat.com, pgonda@...gle.com, peterz@...radead.org,
 srinivas.pandruvada@...ux.intel.com, rientjes@...gle.com, tobin@....com,
 vbabka@...e.cz, kirill@...temov.name, ak@...ux.intel.com,
 tony.luck@...el.com, sathyanarayanan.kuppuswamy@...ux.intel.com,
 alpergun@...gle.com, jarkko@...nel.org, ashish.kalra@....com,
 nikunj.dadhania@....com, pankaj.gupta@....com,
 "liam.merwick@...cle.com Brijesh Singh" <brijesh.singh@....com>
Subject: Re: [PATCH v1 04/26] x86/sev: Add the host SEV-SNP initialization
 support

On 09/01/2024 13:44, Borislav Petkov wrote:
> On Tue, Jan 09, 2024 at 01:29:06PM +0100, Borislav Petkov wrote:
>> At least three issues I see with that:
>>
>> - the allocation can fail so it is a lot more convenient when the
>>   firmware prepares it
>>
>> - the RMP_BASE and RMP_END writes need to be verified they actially did
>>   set up the RMP range because if they haven't, you might as well
>>   throw SNP security out of the window. In general, letting the kernel
>>   do the RMP allocation needs to be verified very very thoroughly.
>>
>> - a future feature might make this more complicated
> 
> - What do you do if you boot on a system which has the RMP already
>   allocated in the BIOS?
> 
> - How do you detect that it is the L1 kernel that must allocate the RMP?
> 
> - Why can't you use the BIOS allocated RMP in your scenario too instead
>   of the L1 kernel allocating it?
> 
> - ...
> 
> I might think of more.
> 

Sorry for not replying back sooner.

I agree, lets get the base SNP stuff in and then talk about extensions.

I want to sync up with Michael to make sure he's onboard with what I'm
proposing. I'll add more design/documentation/usecase descriptions with the
next submission and will make sure to address all the issues you brought up.

Jeremi