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Date:   Wed, 29 Mar 2017 17:21:13 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Borislav Petkov <bp@...e.de>, Brijesh Singh <brijesh.singh@....com>
Cc:     simon.guinot@...uanux.org, linux-efi@...r.kernel.org,
        kvm@...r.kernel.org, rkrcmar@...hat.com, matt@...eblueprint.co.uk,
        linux-pci@...r.kernel.org, linus.walleij@...aro.org,
        gary.hook@....com, linux-mm@...ck.org,
        paul.gortmaker@...driver.com, hpa@...or.com, cl@...ux.com,
        dan.j.williams@...el.com, aarcange@...hat.com,
        sfr@...b.auug.org.au, andriy.shevchenko@...ux.intel.com,
        herbert@...dor.apana.org.au, bhe@...hat.com, xemul@...allels.com,
        joro@...tes.org, x86@...nel.org, peterz@...radead.org,
        piotr.luc@...el.com, mingo@...hat.com, msalter@...hat.com,
        ross.zwisler@...ux.intel.com, dyoung@...hat.com,
        thomas.lendacky@....com, jroedel@...e.de, keescook@...omium.org,
        arnd@...db.de, toshi.kani@....com, mathieu.desnoyers@...icios.com,
        luto@...nel.org, devel@...uxdriverproject.org, bhelgaas@...gle.com,
        tglx@...utronix.de, mchehab@...nel.org, iamjoonsoo.kim@....com,
        labbott@...oraproject.org, tony.luck@...el.com,
        alexandre.bounine@....com, kuleshovmail@...il.com,
        linux-kernel@...r.kernel.org, mcgrof@...nel.org, mst@...hat.com,
        linux-crypto@...r.kernel.org, tj@...nel.org,
        akpm@...ux-foundation.org, davem@...emloft.net
Subject: Re: [RFC PATCH v2 16/32] x86: kvm: Provide support to create Guest
 and HV shared per-CPU variables



On 28/03/2017 20:39, Borislav Petkov wrote:
>> 2) Since the encryption attributes works on PAGE_SIZE hence add some extra
>> padding to 'struct kvm-steal-time' to make it PAGE_SIZE and then at runtime
>> clear the encryption attribute of the full PAGE. The downside of this was
>> now we need to modify structure which may break the compatibility.
> From SEV-ES whitepaper:
> 
> "To facilitate this communication, the SEV-ES architecture defines
> a Guest Hypervisor Communication Block (GHCB). The GHCB resides in
> page of shared memory so it is accessible to both the guest VM and the
> hypervisor."
> 
> So this is kinda begging to be implemented with a shared page between
> guest and host. And then put steal-time, ... etc in there too. Provided
> there's enough room in the single page for the GHCB *and* our stuff.

The GHCB would have to be allocated much earlier, possibly even by
firmware depending on how things will be designed.  I think it's
premature to consider SEV-ES requirements.

Paolo

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