The get_vtl(void) function
* has got one bug when the code started using a wrong pointer type after
refactoring, and also
* the both function in question don't adhere to the requirements of
the Hypervisor Top-Level Funactional Specification[1, 2] as the code overlaps
the input and output areas for a hypercall.
The first issue leads to a wrong 100% reproducible computation due to reading
a byte worth of data at a wrong offset. That in turn leads to using a nonsensical
value ("fortunately", could catch it easily!) for the current VTL when initiating
VMBus communications. As a repercussion from that, the system wouldn't boot. The
fix is straightforward: use the correct pointer type.
The second issue doesn't seem to lead to any reproducible breakage just yet. It is
fixed with using the output hypercall pages allocated per-CPU, and that isn't the
only or the most obvious choice so let me elaborate why that fix appears to be the
best one in my opinion out of the options I could conceive of.
The approach chosen for fixing the second issue makes two things shine through:
* these functions just get a vCPU register, no special treatment needs to be
involved,
* VTLs and dom0 can and should share code as both exist to provide services to
a guest(s), be that from within the partition or from outside of it.
The projected benefits include replacing the functions in question with a future
`hv_get_vp_registers` one shared between dom0 and VTLs to allow for a better test
coverage.
I have validated the fixes by booting the fixed kernel in VTL2 up using OpenVMM and
OpenHCL[3, 4].
[1] https://learn.microsoft.com/en-us/virtualization/hyper-v-on-windows/tlfs/hypercall-interface
[2] https://github.com/MicrosoftDocs/Virtualization-Documentation/tree/main/tlfs
[3] https://openvmm.dev/guide/user_guide/openhcl.html
[4] https://github.com/microsoft/OpenVMM
[v5]
- In the first patch, removed some arch-specific #ifdef guards to fix the
arm64 build and stick to the direction chosen for the Hyper-V header files.
I could not remove all of them as some interrupt state structures
are defined differently for x64 and arm64 and are found in the same
enclosing `union hv_register_value`.
No changes to other patches (approved in v4).
[v4]: https://lore.kernel.org/lkml/20241227183155.122827-1-romank@xxxxxxxxxxxxxxxxxxx/
- Wrapped DECLARE_FLEX_ARRAY into a struct and added one more
member as the documentation requires,
- Removed superfluous type coercion,
- Fixed tags,
- Rebased onto the latest hyperv-next branch.
[v3]: https://lore.kernel.org/lkml/20241226213110.899497-1-romank@xxxxxxxxxxxxxxxxxxx/
- Added a fix for hv_vtl_apicid_to_vp_id(),
- Split out the patch for enabling the hypercall output page,
- Updated the title of the patch series,
[v2]: https://lore.kernel.org/lkml/20241226203050.800524-1-romank@xxxxxxxxxxxxxxxxxxx/
- Used the suggestions to define an additional structure to improve code readability,
- Split out the patch with that definition.
[v1]: https://lore.kernel.org/lkml/20241218205421.319969-1-romank@xxxxxxxxxxxxxxxxxxx/
Roman Kisel (5):
hyperv: Define struct hv_output_get_vp_registers
hyperv: Fix pointer type in get_vtl(void)
hyperv: Enable the hypercall output page for the VTL mode
hyperv: Do not overlap the hvcall IO areas in get_vtl()
hyperv: Do not overlap the hvcall IO areas in hv_vtl_apicid_to_vp_id()
arch/x86/hyperv/hv_init.c | 6 ++---
arch/x86/hyperv/hv_vtl.c | 2 +-
drivers/hv/hv_common.c | 6 ++---
include/hyperv/hvgdk_mini.h | 49 +++++++++++++++++++++++++++++++++++++
4 files changed, 56 insertions(+), 7 deletions(-)
base-commit: 26e1b813fcd02984b1cac5f3decdf4b0bb56fe02
--
2.34.1
