[PATCH v2 00/14] KVM: arm64: NV userspace ABI

[Joey Gouly]

On Thu, Feb 20, 2025 at 01:48:53PM +0000, Marc Zyngier wrote:
> Since the previous incarnation of the ABI was proved to be subtly
> wrong, I have reworked it to be more in line with the current way KVM
> operates.
> 
> No more late NV-specific adjustment nor writable ID_AA64MMFR0_EL1.VH.
> The NV configuration is now entirely selected from the vcpu flags.
> I've preserved the KVM_ARM_VCPU_EL2 flag which enables NV with VHE,
> and added KVM_ARM_VCPU_EL2_E2H0 which alters the NV behaviour to only
> allow nVHE guests without recursive NV support.
> 
> This series is actually very little new code. The bulk of it is
> converting the feature downgrade to be per-idreg, essentially going
> back to the state before 44241f34fac96 ("KVM: arm64: nv: Use accessors
> for modifying ID registers"), only slightly modernised. This then
> becomes part of the reset value computing.
> 
> The rest is simply what you'd expect in terms of being able to write
> the ID_AA64MMFR4_EL1.NV_frac field, making the correct bits RES0 when
> needed, probing for capabilities and handling the init flags.
> 
> Patches on top of -rc3, with the integration branch at the usual
> location.
> 
> * From v1 [1]
> 
>   - Fixed mishandling of ID_UNALLOCATED(), resulting in extra
>     consolidation and simplify the macro maze a bit
> 
>   - Picked up Oliver's RBs (thanks!)
> 
>   - Rebased on top of -rc3
> 
> [1] https://lore.kernel.org/r/20250215173816.3767330-1-maz@kernel.org
> 
> Marc Zyngier (14):
>   arm64: cpufeature: Handle NV_frac as a synonym of NV2
>   KVM: arm64: Hide ID_AA64MMFR2_EL1.NV from guest and userspace
>   KVM: arm64: Mark HCR.EL2.E2H RES0 when ID_AA64MMFR1_EL1.VH is zero
>   KVM: arm64: Mark HCR.EL2.{NV*,AT} RES0 when ID_AA64MMFR4_EL1.NV_frac
>     is 0
>   KVM: arm64: Advertise NV2 in the boot messages
>   KVM: arm64: Consolidate idreg callbacks
>   KVM: arm64: Make ID_REG_LIMIT_FIELD_ENUM() more widely available
>   KVM: arm64: Enforce NV limits on a per-idregs basis
>   KVM: arm64: Move NV-specific capping to idreg sanitisation
>   KVM: arm64: Allow userspace to limit NV support to nVHE
>   KVM: arm64: Make ID_AA64MMFR4_EL1.NV_frac writable
>   KVM: arm64: Advertise FEAT_ECV when possible
>   KVM: arm64: Allow userspace to request KVM_ARM_VCPU_EL2*
>   KVM: arm64: Document NV caps and vcpu flags
> 
>  Documentation/virt/kvm/api.rst      |  14 +-
>  arch/arm64/include/asm/kvm_host.h   |   2 +-
>  arch/arm64/include/asm/kvm_nested.h |   1 +
>  arch/arm64/include/uapi/asm/kvm.h   |   1 +
>  arch/arm64/kernel/cpufeature.c      |  15 +-
>  arch/arm64/kvm/arm.c                |  11 +-
>  arch/arm64/kvm/nested.c             | 285 +++++++++++++++-------------
>  arch/arm64/kvm/sys_regs.c           |  44 ++---
>  arch/arm64/kvm/sys_regs.h           |  10 +
>  include/uapi/linux/kvm.h            |   2 +
>  10 files changed, 217 insertions(+), 168 deletions(-)
> 

Reviewed-by: Joey Gouly <joey.gouly at arm.com>