[PATCH v2 00/20] KVM: arm64: Generalise RESx handling

[Fuad Tabba]

Hi Marc,

For the series:
Tested-by: Fuad Tabba <tabba at google.com>

Thanks!
/fuad

On Mon, 2 Feb 2026 at 18:43, Marc Zyngier <maz at kernel.org> wrote:
>
> Having spent some time dealing with some dark corners of the
> architecture, I have realised that our RESx handling is a bit patchy.
> Specially when it comes to RES1 bits, which are not clearly defined in
> config.c, and rely on band-aids such as FIXED_VALUE.
>
> This series takes the excuse of adding SCTLR_EL2 sanitisation to bite
> the bullet and pursue several goals:
>
> - clearly define bits that are RES1 when a feature is absent
>
> - have a unified data structure to manage both RES0 and RES1 bits
>
> - deal with the annoying complexity of some features being
>   conditioned on E2H==1
>
> - allow a single bit to take different RESx values depending on the
>   value of E2H
>
> This allows quite a bit of cleanup, including the total removal of the
> FIXED_VALUE horror, which was always a bizarre construct. We also get
> a new debugfs file to introspect the RESx settings for a given guest.
>
> Overall, this lowers the complexity of expressing the configuration
> constraints, for very little code (most of the extra lines are
> introduced by the debugfs stuff, and SCTLR_EL2 being added to the
> sysreg file).
>
> Patches on top of my kvm-arm64/vtcr branch (which is currently
> simmering in -next).
>
> * From v1 [1]
>
>   - Simplified RES0 handling by dropping the RES0_WHEN_E2Hx macros
>
>   - Cleaned up the kvm_{g,s}et_sysreg_resx() helpers
>
>   - Simplified dynamic RESx handling
>
>   - New improved debugfs handling, thanks to Fuad!
>
>   - Various clean-ups and spelling fixes
>
>   - Collected RBs (thanks Fuad and Joey!)
>
> [1] https://lore.kernel.org/all/20260126121655.1641736-1-maz@kernel.org
> Marc Zyngier (20):
>   arm64: Convert SCTLR_EL2 to sysreg infrastructure
>   KVM: arm64: Remove duplicate configuration for SCTLR_EL1.{EE,E0E}
>   KVM: arm64: Introduce standalone FGU computing primitive
>   KVM: arm64: Introduce data structure tracking both RES0 and RES1 bits
>   KVM: arm64: Extend unified RESx handling to runtime sanitisation
>   KVM: arm64: Inherit RESx bits from FGT register descriptors
>   KVM: arm64: Allow RES1 bits to be inferred from configuration
>   KVM: arm64: Correctly handle SCTLR_EL1 RES1 bits for unsupported
>     features
>   KVM: arm64: Convert HCR_EL2.RW to AS_RES1
>   KVM: arm64: Simplify FIXED_VALUE handling
>   KVM: arm64: Add REQUIRES_E2H1 constraint as configuration flags
>   KVM: arm64: Add RES1_WHEN_E2Hx constraints as configuration flags
>   KVM: arm64: Move RESx into individual register descriptors
>   KVM: arm64: Simplify handling of HCR_EL2.E2H RESx
>   KVM: arm64: Get rid of FIXED_VALUE altogether
>   KVM: arm64: Simplify handling of full register invalid constraint
>   KVM: arm64: Remove all traces of FEAT_TME
>   KVM: arm64: Remove all traces of HCR_EL2.MIOCNCE
>   KVM: arm64: Add sanitisation to SCTLR_EL2
>   KVM: arm64: Add debugfs file dumping computed RESx values
>
>  arch/arm64/include/asm/kvm_host.h             |  38 +-
>  arch/arm64/include/asm/sysreg.h               |   7 -
>  arch/arm64/kvm/config.c                       | 427 ++++++++++--------
>  arch/arm64/kvm/emulate-nested.c               |  10 +-
>  arch/arm64/kvm/nested.c                       | 151 +++----
>  arch/arm64/kvm/sys_regs.c                     |  68 +++
>  arch/arm64/tools/sysreg                       |  82 +++-
>  tools/arch/arm64/include/asm/sysreg.h         |   6 -
>  tools/perf/Documentation/perf-arm-spe.txt     |   1 -
>  .../testing/selftests/kvm/arm64/set_id_regs.c |   1 -
>  10 files changed, 478 insertions(+), 313 deletions(-)
>
> --
> 2.47.3
>