[v2,0/3] Introduce CONFIG_MSHV_ROOT for root partition code

Message

Nuno Das Neves Feb. 20, 2025, 6:33 p.m. UTC

Running in the root partition is a unique and specialized case that
requires additional code. CONFIG_MSHV_ROOT allows Hyper-V guest kernels
to exclude this code, which is important since significant additional code
specific to the root partition is expected to be added over time.

To do this, change hv_root_partition to be a function which is stubbed out
to return false if CONFIG_MSHV_ROOT=n, and don't compile hv_proc.c at all,
stubbing out those functions with inline versions.

Store the partition type (guest or root) in an enum hv_current_partition_type,
which can be extended beyond just guest and root partition.

While at it, introduce hv_result_to_errno() to convert Hyper-V status codes
to regular linux errors. This is useful because the caller of a hypercall
helper function (such as those in hv_proc.c) usually can't and doesn't
interpret the Hyper-V status, so it is better to convert it to an error code
and reduce the possibility of misinterpreting it. This also alows the stubbed
versions of the hv_proc.c functions to just return a linux error code.

Signed-off-by: Nuno Das Neves <[e-mail]>
---
Changes in v2:
* Add patch to convert hypercall statuses to linux error codes [Easwar
  Hariharan]
* While at it, split the original patch into two logical pieces, one to change
  hv_root_partition into a function, and one to introduce MSHV_CONFIG_ROOT
* Improve the clarity of and add an error message to
  hv_identify_partition_type() [Easwar Hariharan] [Michael Kelley]
* Better explain *why* the patches are useful, in the commit messages [Michael
  Kelley]
* Add a Kconfig comment explaining why PAGE_SIZE_4KB is needed [Michael Kelley]
* Minor style and typo fixes

Nuno Das Neves (3):
  hyperv: Convert hypercall statuses to linux error codes
  hyperv: Change hv_root_partition into a function
  hyperv: Add CONFIG_MSHV_ROOT to gate root partition support

 arch/arm64/hyperv/mshyperv.c       |  2 +
 arch/x86/hyperv/hv_init.c          | 10 ++---
 arch/x86/kernel/cpu/mshyperv.c     | 24 +----------
 drivers/clocksource/hyperv_timer.c |  4 +-
 drivers/hv/Kconfig                 | 16 +++++++
 drivers/hv/Makefile                |  3 +-
 drivers/hv/hv.c                    | 10 ++---
 drivers/hv/hv_common.c             | 69 +++++++++++++++++++++++++++---
 drivers/hv/hv_proc.c               |  6 +--
 drivers/hv/vmbus_drv.c             |  2 +-
 drivers/iommu/hyperv-iommu.c       |  4 +-
 include/asm-generic/mshyperv.h     | 40 ++++++++++++++---
 12 files changed, 137 insertions(+), 53 deletions(-)