linux-kernel - Re: [PATCH Part1 RFC v3 11/22] x86/sev: Add helper for validating pages in early enc attribute changes

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Date:   Mon, 14 Jun 2021 21:03:03 +0200
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,
        linux-crypto@...r.kernel.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>,
        Wanpeng Li <wanpengli@...cent.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>, tony.luck@...el.com,
        npmccallum@...hat.com
Subject: Re: [PATCH Part1 RFC v3 11/22] x86/sev: Add helper for validating
 pages in early enc attribute changes

On Mon, Jun 14, 2021 at 07:45:11AM -0500, Brijesh Singh wrote:
> IMO, there is no need to add a warning. This case should happen if its
> either a hypervisor bug or hypervisor does not follow the GHCB
> specification. I followed the SEV-ES vmgexit handling  and it does not
> warn if the hypervisor returns a wrong response code. We simply
> terminate the guest.

This brings my regular user-friendliness question: will the guest user
know what happened or will the guest simply disappear/freeze without any
hint as to what has happened so that a post-mortem analysis would turn
out hard to decipher?

> I did thought about reusing the VMGEXIT defined macro
> SNP_PAGE_STATE_{PRIVATE, SHARED} but I was not sure if you will be okay
> with that.

Yeah, I think that makes stuff simpler. Unless there's something
speaking against it which we both are not thinking of right now.

> Additionally now both the function name and macro name will
> include the "SNP". The call will look like this:
> 
> snp_prep_memory(paddr, SNP_PAGE_STATE_PRIVATE)

Yap, looks ok to me.

Thx.

-- 
Regards/Gruss,
    Boris.

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