linux-kernel - Re: [PATCH Part1 RFC v2 13/20] x86/sev: Register GHCB memory when SEV-SNP is active

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Date:   Tue, 25 May 2021 09:47:24 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     brijesh.singh@....com, x86@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        tglx@...utronix.de, jroedel@...e.de, thomas.lendacky@....com,
        pbonzini@...hat.com, mingo@...hat.com, dave.hansen@...el.com,
        rientjes@...gle.com, seanjc@...gle.com, peterz@...radead.org,
        hpa@...or.com, tony.luck@...el.com
Subject: Re: [PATCH Part1 RFC v2 13/20] x86/sev: Register GHCB memory when
 SEV-SNP is active


On 5/25/21 9:35 AM, Borislav Petkov wrote:
>> In this particular case, the snp_register_ghcb() is shared between the
>> decompress and main kernel. The variable data->snp_ghcb_registered is
>> not visible in the decompressed path,
> Why is it not visible?

Maybe I should have said, its not applicable in the decompressed path.

The snp_ghcb_register is defined in the per-CPU structure, and used in
the per-CPU #VC handler. We don't have the per-CPU #VC handler in the
decompression code path.

Please see the arch/x86/kernel/sev.c

/* #VC handler runtime per-CPU data */

struct sev_es_runtime_data {

 ...

 ...

 bool snp_ghcb_registered;

}