From:   "Michael Kelley (LINUX)" <mikelley@microsoft.com>
To:     Borislav Petkov <bp@alien8.de>,
        Sean Christopherson <seanjc@google.com>
CC:     Dave Hansen <dave.hansen@intel.com>,
        "hpa@zytor.com" <hpa@zytor.com>, KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        "wei.liu@kernel.org" <wei.liu@kernel.org>,
        Dexuan Cui <decui@microsoft.com>,
        "luto@kernel.org" <luto@kernel.org>,
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        "lpieralisi@kernel.org" <lpieralisi@kernel.org>,
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        Tianyu Lan <Tianyu.Lan@microsoft.com>,
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        "jane.chu@oracle.com" <jane.chu@oracle.com>,
        "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+inmE0Kn2DbFJZ3EJa6nyiwAgAAUafCAB237AIAL8mwQgAhWY4CAAeE2AIABk95AgAGmoACAAAYigIAAAicAgAAHCQCAAAYXAIAADqWAgAAB8ICAAAP2cIAAK2uAgAjCToCAACg1IA==
Date:   Thu, 16 Feb 2023 16:16:16 +0000
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From: Borislav Petkov <bp@alien8.de> Sent: Thursday, February 16, 2023 5:33=
 AM
>=20
> On Fri, Feb 10, 2023 at 11:47:27PM +0000, Sean Christopherson wrote:
> > I agree with Boris' comment that a one-off "other encrypted range" is a=
 hack, but
> > that's just an API problem.  The kernel already has hypervisor specific=
 hooks (and
> > for SEV-ES even), why not expand that?  That way figuring out which dev=
ices are
> > private is wholly contained in Hyper-V code, at least until there's a g=
eneric
> > solution for enumerating private devices, though that seems unlikely to=
 happen
> > and will be a happy problem to solve if it does come about.
>=20
> I feel ya and this all makes sense and your proposals look clean enough
> to me but we still need some way of determining whether this is a vTOM
> on hyperv=20

Historically, callbacks like Sean proposed default to NULL and do nothing
unless they are explicitly set.  The Hyper-V vTOM code would set the callba=
ck.
Is that not sufficient?  Or in the two places where the callback would
be made, do you want to bracket with a test for being in a Hyper-V vTOM
VM?  If so, then we're back to needing something like CC_ATTR_PARAVISOR
on which to gate the callbacks.

Or do you mean something else entirely?

Michael

> because there's the next crapola with
>=20
> https://lore.kernel.org/all/20230209072220.6836-4-jgross@suse.com/
>=20
> because apparently hyperv does PAT but disables MTRRs for such vTOM
> SEV-SNP guests and ... madness.
>=20
> But that's not the only example - Xen has been doing this thing too.
>=20
> And J=FCrgen has been trying to address this in a clean way but it is
> a pain.
>=20
> What I don't want to have is a gazillion ways to check what needs to
> happen for which guest type. Because people who change the kernel to run
> on baremetal, will break them. And I can't blame them. We try to support
> all kinds of guests in the x86 code but this support should be plain and
> simple.
>=20