linux-kernel - Re: [PATCH v8 36/40] x86/sev: Provide support for SNP guest request NAEs

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Date:   Sat, 29 Jan 2022 13:02:18 +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 v8 36/40] x86/sev: Provide support for SNP guest request
 NAEs

On Sat, Jan 29, 2022 at 05:49:06AM -0600, Brijesh Singh wrote:
> The hypervisor must validate that the guest has supplied enough pages to
> hold the certificates that will be returned before performing the SNP
> guest request. If there are not enough guest pages to hold the
> certificate table and certificate data, the hypervisor will return the
> required number of pages needed to hold the certificate table and
> certificate data in the RBX register and set the SW_EXITINFO2 field to
> 0x0000000100000000.

Then you could call that one:

#define SNP_GUEST_REQ_ERR_NUM_PAGES       BIT_ULL(32)

or so, to mean what exactly that error is. Because when you read the
code, it is more "self-descriptive" this way:

	...
	ghcb->save.sw_exit_info_2 == SNP_GUEST_REQ_ERR_NUM_PAGES)
		input->data_npages = ghcb_get_rbx(ghcb);

> It does not spell it as invalid length. However, for *similar* failure,
> the SEV-SNP spec spells out it as INVALID_LENGTH, so, I choose macro
> name as INVALID_LENGTH.

You can simply define a separate one here called ...INVALID_LENGTH.

Thx.

-- 
Regards/Gruss,
    Boris.

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