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

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Message-ID: <BYAPR12MB275984F14B1E103935A103D98EB29@BYAPR12MB2759.namprd12.prod.outlook.com>
Date:   Wed, 22 Jun 2022 19:43:24 +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

[AMD Official Use Only - General]


-----Original Message-----
From: Dave Hansen <dave.hansen@...el.com> 
Sent: Wednesday, June 22, 2022 1:43 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 11:34, Kalra, Ashish wrote:
>>> So, if the RMP entry format changes in future processors, how do we 
>>> make sure that the kernel does not try to use *this* code on those 
>>> processors?
>> Functions snp_lookup_rmpentry() and dump_rmpentry() which rely on this 
>> structure definition will need to handle it accordingly.

>In other words, old kernels will break on new hardware?

>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.

Thanks,
Ashish