From:   "Michael Kelley (LINUX)" <mikelley@microsoft.com>
To:     Borislav Petkov <bp@alien8.de>
CC:     Sean Christopherson <seanjc@google.com>,
        Dave Hansen <dave.hansen@intel.com>,
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        "tony.luck@intel.com" <tony.luck@intel.com>,
        "x86@kernel.org" <x86@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
        "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
        "iommu@lists.linux.dev" <iommu@lists.linux.dev>
Subject: RE: [PATCH v5 06/14] x86/ioremap: Support hypervisor specified range
 to map as encrypted
Thread-Topic: [PATCH v5 06/14] x86/ioremap: Support hypervisor specified range
 to map as encrypted
Thread-Index: AQHZJs7d1RPl+inmE0Kn2DbFJZ3EJa6nyiwAgAAUafCAB237AIAL8mwQgAhWY4CAAeE2AIABk95AgAGmoACAAAYigIAAAicAgAAHCQCAAAYXAIAADqWAgAAB8ICAAAP2cIAAK2uAgAjCToCAACg1IIAAE3gAgAC0MPA=
Date:   Fri, 17 Feb 2023 06:16:56 +0000
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From: Borislav Petkov <bp@alien8.de> Sent: Thursday, February 16, 2023 9:07=
 AM
>=20
> ... here.
>=20
> We need a single way to test for this guest type and stick with it.
>=20
> I'd like for all guest types we support to be queried in a plain and
> simple way.
>=20
> Not:
>=20
> * CC_ATTR_GUEST_MEM_ENCRYPT
>=20
> * x86_platform.hyper.is_private_mmio(addr)
>=20
> * CC_ATTR_PARAVISOR
>=20
> to mean three different aspects of SEV-SNP guests using vTOM on Hyper-V.
>=20
> This is going to be a major mess which we won't support.
>=20

OK, I'm trying to figure out where to go next.  I've been following the pat=
tern
set by the SEV/SEV-ES/SEV-SNP and TDX platforms in the cc_platform_has()
function.   Each platform returns "true" for multiple CC_ATTR_* values,
and those CC_ATTR_* values are tested in multiple places throughout
kernel code.  Some CC_ATTR_* values are shared by multiple platforms
(like CC_ATTR_GUEST_MEM_ENCRYPT) and some are unique to a particular
platform (like CC_ATTR_HOTPLUG_DISABLED).  For the CC_ATTR_* values
that are shared, the logic of which platforms they apply to occurs once in
cc_platform_has() rather than scattered and duplicated throughout the
kernel, which makes sense.  Any given platform is not represented by a
single CC_ATTR_* value, but by multiple ones.  Each CC_ATTR_* value=20
essentially represents a chunk of kernel functionality that one or more
platforms need, and the platform indicates its need by cc_platform_has()
returning "true" for that value.

So I've been trying to apply the same pattern to the SNP vTOM sub-case
of SEV-SNP.   Is that consistent with your thinking, or is the whole
cc_platform_has() approach problematic, including for the existing
SEV flavors and for TDX?

Michael