linux-kernel - Re: [PATCH v6 14/42] x86/sev: Register GHCB memory when SEV-SNP is active

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Date:   Thu, 4 Nov 2021 14:58:49 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sergio Lopez <slp@...hat.com>, Peter Gonda <pgonda@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Michael Roth <michael.roth@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Andi Kleen <ak@...ux.intel.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com
Subject: Re: [PATCH v6 14/42] x86/sev: Register GHCB memory when SEV-SNP is
 active

On Wed, Nov 03, 2021 at 03:10:16PM -0500, Brijesh Singh wrote:
> Looking at the secondary CPU bring up path it seems that we will not be
> getting #VC until the early_setup_idt() is called. I am thinking to add
> function to register the GHCB from the early_setup_idt()
> 
> early_setup_idt()
> {
>   ...
>   if (IS_ENABLED(CONFIG_MEM_ENCRYPT))
>     sev_snp_register_ghcb()
>   ...
> }
> 
> The above will cover the APs

That will cover the APs during early boot as that is being called from
asm.

> and for BSP case I can call the same function just after the final IDT
> is loaded

Why after and not before?

> cpu_init_exception_handling()
> {
>    ...
>    ...
>    /* Finally load the IDT */
>    load_current_idt();
> 
>    if (IS_ENABLED(CONFIG_MEM_ENCRYPT))
>      sev_snp_register_ghcb()
> 
> }

That is also called on the APs - not only the BSP. trap_init() calls it
from start_kernel() which is the BSP and cpu_init_secondary() calls it
too, which is ofc the APs.

I guess that should be ok since you're calling the same function from
both but WTH do I know...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette