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:   Wed, 16 Jun 2021 09:36:19 -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,
        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 6/16/2021 8:10 AM, Brijesh Singh wrote:
> 
> On 6/16/21 8:02 AM, Borislav Petkov wrote:
>> On Wed, Jun 16, 2021 at 07:49:25AM -0500, Brijesh Singh wrote:
>>> If you still think ...
>> I think you should answer my question first:
>>
>>> Imagine you're a guest owner and you haven't written the SNP code and
>>> you don't know how it works.
>>>
>>> You start a guest in the public cloud and it fails because the
>>> hypervisor violates the GHCB protocol and all that guest prints before
>>> it dies is
>>>
>>> "general request termination"
>>>
>>> How are you - the guest owner - going to find out what exactly happened?
>>>
>>> Call support?
>> And let me paraphrase it again: if the error condition with which the
>> guest terminates is not uniquely identifiable but simply a "general
>> request", how are such conditions going to be debugged?
> > I thought I said it somewhere in our previous conversation, I would look
> at the KVM trace log, each vmgexit entry and exit are logged. The log
> contains full GHCB MSR value, and in it you can see both the request and
> response code and decode the failure reason.
> 

I now realized that in this case we may not have the trace's. It's
a production environment and my development machine :(. I will go ahead and
add the error message when guest sees an invalid response code before
terminating it. Will do the similar error message in the decompression
path.

-Brijesh