linux-kernel - RE: [PATCH Part2 v6 05/49] x86/sev: Add RMP entry lookup helpers

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Message-ID: <BYAPR12MB2759B4A927143CAC45B49E1C8EB29@BYAPR12MB2759.namprd12.prod.outlook.com>
Date:   Wed, 22 Jun 2022 20:58:18 +0000
From:   "Kalra, Ashish" <Ashish.Kalra@....com>
To:     Dave Hansen <dave.hansen@...el.com>,
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Subject: RE: [PATCH Part2 v6 05/49] x86/sev: Add RMP entry lookup helpers

[Public]

From: Dave Hansen <dave.hansen@...el.com>
Sent: Wednesday, June 22, 2022 2:50 PM
To: Kalra, Ashish <Ashish.Kalra@....com>; x86@...nel.org; linux-kernel@...r.kernel.org; kvm@...r.kernel.org; linux-coco@...ts.linux.dev; linux-mm@...ck.org; linux-crypto@...r.kernel.org
Cc: tglx@...utronix.de; mingo@...hat.com; jroedel@...e.de; Lendacky, Thomas <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; dovmurik@...ux.ibm.com; tobin@....com; bp@...en8.de; Roth, Michael <Michael.Roth@....com>; vbabka@...e.cz; kirill@...temov.name; ak@...ux.intel.com; tony.luck@...el.com; marcorr@...gle.com; sathyanarayanan.kuppuswamy@...ux.intel.com; alpergun@...gle.com; dgilbert@...hat.com; jarkko@...nel.org
Subject: Re: [PATCH Part2 v6 05/49] x86/sev: Add RMP entry lookup helpers

On 6/22/22 12:43, Kalra, Ashish wrote:
>>> I think that needs to be fixed.  It should be as simple as a 
>>> model/family check, though.  If someone (for example) attempts to 
>>> use SNP (and thus snp_lookup_rmpentry() and dump_rmpentry()) code on 
>>> a newer CPU, the kernel should refuse.
>> More specifically I am thinking of adding RMP entry field accessors 
>> so that they can do this cpu model/family check and return the 
>> correct field as per processor architecture.

>That will be helpful down the road when there's more than one format.
>But, the real issue is that the kernel doesn't *support* a different RMP format.  So, the SNP support should be disabled when encountering a model/family other than the known good one.

>Yes, that makes sense, will add an additional check in snp_rmptable_init().

Also to add here,  additionally we may create an architectural way to read the RMP entry in the future.

Thanks,
Ashish