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

Kalra, Ashish
2022-06-22T20:58:35Z

[Public]

From: Dave Hansen <dave.hansen@intel.com>
Sent: Wednesday, June 22, 2022 2:50 PM
To: Kalra, Ashish <Ashish.Kalra@amd.com>; x86@kernel.org; linux-kernel@vger.kernel.org; kvm@vger.kernel.org; linux-coco@lists.linux.dev; linux-mm@kvack.org; linux-crypto@vger.kernel.org
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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