linux-kernel - Re: [RFC PATCH v1 09/28] x86/efi: Access EFI data as encrypted when SEV is active

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Date:   Thu, 22 Sep 2016 22:10:40 +0200
From:   Borislav Petkov <bp@...e.de>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Brijesh Singh <brijesh.singh@....com>,
        simon.guinot@...uanux.org, linux-efi@...r.kernel.org,
        kvm@...r.kernel.org, rkrcmar@...hat.com, matt@...eblueprint.co.uk,
        linus.walleij@...aro.org, linux-mm@...ck.org,
        paul.gortmaker@...driver.com, hpa@...or.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, mingo@...hat.com,
        msalter@...hat.com, ross.zwisler@...ux.intel.com,
        dyoung@...hat.com, jroedel@...e.de, keescook@...omium.org,
        toshi.kani@....com, mathieu.desnoyers@...icios.com,
        devel@...uxdriverproject.org, 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,
        linux-crypto@...r.kernel.org, akpm@...ux-foundation.org,
        davem@...emloft.net
Subject: Re: [RFC PATCH v1 09/28] x86/efi: Access EFI data as encrypted when
 SEV is active

On Thu, Sep 22, 2016 at 02:49:22PM -0500, Tom Lendacky wrote:
> > I thought that reduction is the reservation of bits for the SME mask.
> > 
> > What other reduction is there?
> 
> There is a reduction in physical address space for the SME mask and the
> bits used to aid in identifying the ASID associated with the memory
> request. This allows for the memory controller to determine the key to
> be used for the encryption operation (host/hypervisor key vs. an SEV
> guest key).

Ok, I think I see what you mean: you call SME mask the bit in CPUID
Fn8000_001F[EBX][5:0], i.e., the C-bit, i.e. sme_me_mask. And the other
reduction is the key ASID, i.e., CPUID Fn8000_001F[EBX][11:6], i.e.
sme_me_loss.

I think we're on the same page - I was simply calling everything SME
mask because both are together in the PTE:

"Additionally, in some implementations, the physical address size of the
processor may be reduced when memory encryption features are enabled,
for example from 48 to 43 bits."

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--