[PATCH v4 0/8] TDX host: metadata reading tweaks, bug fix and info dump

Kai Huang
2024-09-24T11:29:09Z

TL;DR:

This series does necessary tweaks to TDX host "global metadata" reading
code to fix some immediate issues in the TDX module initialization code,
with intention to also provide a flexible code base to support sharing
global metadata to KVM (and other kernel components) for future needs.

This series, and additional patches to initialize TDX when loading KVM
module and read essential metadata fields for KVM TDX can be found at
[1].

Hi Dave (and maintainers),

This series targets x86 tip. Also add Dan, KVM maintainers and KVM list
so people can also review and comment.

This is a pre-work of the "quite near future" KVM TDX support (see the
kvm-coco-queue branch [2], which already includes all the patches in the
v2 of this series). I appreciate if you can review, comment and take
this series if the patches look good to you.

v3 -> v4:
- Change to add a build_sysmd_read(_size) macro to build one primitive
for each metadata field element size, similar to build_mmio_read()
macro -- Dan.

https://lore.kernel.org/kvm/66db75497a213_22a2294b@dwillia2-xfh.jf.intel.com.notmuch/

- Replace TD_SYSINFO_MAP() with READ_SYS_INFO() and #undef it after
use -- Adrian, Dan.

https://lore.kernel.org/kvm/66db7469dbfdd_22a2294c0@dwillia2-xfh.jf.intel.com.notmuch/

- Use permalink in the changelog -- Dan.
- Other comments from Dan, Adrian and Nikolay. Please see individual
patches.
- Collect tags from Dan, Adrian, Nikolay (Thanks!).

v3: https://lore.kernel.org/kvm/5235e05e-1d73-4f70-9b5d-b8648b1f4524@intel.com/T/

v2 -> v3 (address comments from Dan):
- Replace the first couple of "metadata reading tweaks" patches with
two new patches using a different approach (removin the 'struct
field_mapping' and reimplement the TD_SYSINFO_MAP()):

https://lore.kernel.org/kvm/a107b067-861d-43f4-86b5-29271cb93dad@intel.com/T/#m7cfb3c146214d94b24e978eeb8708d92c0b14ac6
https://lore.kernel.org/kvm/a107b067-861d-43f4-86b5-29271cb93dad@intel.com/T/#mbe65f0903ff7835bc418a907f0d02d7a9e0b78be
https://lore.kernel.org/kvm/a107b067-861d-43f4-86b5-29271cb93dad@intel.com/T/#m80cde5e6504b3af74d933ea0cbfc3ca9d24697d3

- Split out the renaming of 'struct tdx_tdmr_sysinfo' as a separate
patch and place it at the beginning of this series.

https://lore.kernel.org/kvm/cover.1721186590.git.kai.huang@intel.com/T/#m8fec7c429242d640cf5e756eb68e3b822e6dff8b

- Refine this cover letter ("More info" section)

https://lore.kernel.org/kvm/cover.1721186590.git.kai.huang@intel.com/T/#m11868c9f486dcc4cfbbb690c7c18dfa4570e433f

- Address other comments. See changelog of individual patches.

v2: https://lore.kernel.org/kvm/cover.1721186590.git.kai.huang@intel.com/T/

v1 -> v2:
- Fix comments from Chao and Nikolay.
- A new patch to refine an out-dated comment by Nikolay.
- Collect tags from Nikolay (thanks!).

v1: https://lore.kernel.org/linux-kernel/cover.1718538552.git.kai.huang@intel.com/T/

=== More info ===

TDX module provides a set of "global metadata fields" for software to
query. They report things like TDX module version, supported features
fields required for creating TDX guests and so on.

Today the TDX host code already reads "TD Memory Region" (TDMR) related
metadata fields for module initialization. There are immediate needs
that require TDX host code to read more metadata fields:

- Dump basic TDX module info [3];
- Reject module with no NO_RBP_MOD feature support [4];
- Read CMR info to fix a module initialization failure bug [5].

Also, the "quite near future" KVM TDX support requires to read more
global metadata fields. In the longer term, the TDX Connect [6] (which
supports assigning trusted IO devices to TDX guest) may also require
other kernel components (e.g., pci/vt-d) to access more metadata.

To meet all of those, the idea is the TDX host core-kernel to provide a
centralized, canonical, and read-only structure to contain all global
metadata that comes out of TDX module for all kernel components to use.

An alternative way is to expose metadata reading API(s) for in-kernel
TDX users to use, but the reasons of choosing to provide a centural
structure are, quoted from Dan:

The idea that x86 gets to review growth to this structure over time is
an asset for maintainability and oversight of what is happening in the
downstream consumers like KVM and TSM (for TDX Connect).

A dynamic retrieval API removes that natural auditing of data structure
patches from tip.git.

Yes, it requires more touches than letting use cases consume new
metadata fields at will, but that's net positive for maintainence of
the kernel and the feedback loop to the TDX module.

This series starts to track all global metadata fields into a single
'struct tdx_sys_info', and reads more metadata fields to that structure
to address the immediate needs as mentioned above.

More fields will be added to support KVM TDX. For the initial support
all metadata fields are populated in this single structure and shared to
KVM via a 'const pointer' to that structure (see last patches in [1]).

[1] https://github.com/intel/tdx/commits/kvm-tdxinit-host-metadata-v4/
[2] https://git.kernel.org/pub/scm/virt/kvm/kvm.git/log/?h=kvm-coco-queue
[3] https://lore.kernel.org/lkml/4b3adb59-50ea-419e-ad02-e19e8ca20dee@intel.com/
[4] https://lore.kernel.org/lkml/fc0e8ab7-86d4-4428-be31-82e1ece6dd21@intel.com/
[5] https://github.com/canonical/tdx/issues/135#issuecomment-2151570238
[6] https://cdrdv2.intel.com/v1/dl/getContent/773614

Kai Huang (8):
x86/virt/tdx: Rename 'struct tdx_tdmr_sysinfo' to reflect the spec
better
x86/virt/tdx: Rework TD_SYSINFO_MAP to support build-time verification
x86/virt/tdx: Prepare to support reading other global metadata fields
x86/virt/tdx: Refine a comment to reflect the latest TDX spec
x86/virt/tdx: Start to track all global metadata in one structure
x86/virt/tdx: Print TDX module version
x86/virt/tdx: Require the module to assert it has the NO_RBP_MOD
mitigation
x86/virt/tdx: Reduce TDMR's reserved areas by using CMRs to find
memory holes

arch/x86/virt/vmx/tdx/tdx.c | 282 +++++++++++++++++++++++++++---------
arch/x86/virt/vmx/tdx/tdx.h | 85 ++++++++++-
2 files changed, 294 insertions(+), 73 deletions(-)

base-commit: a6f489fee2633f8595934a850981bd4284abdbba
--
2.46.0