This series introduces initial support for the SCTLR2_ELx registers in Linux.
The feature is optional starting from ARMv8.8/ARMv9.3,
and becomes mandatory from ARMv8.9/ARMv9.4.

Currently, Linux has no strict need to modify SCTLR2_ELx—
at least assuming that firmware initializes
these registers to reasonable defaults.

However, several upcoming architectural features will require configuring
control bits in these registers.
Notable examples include FEAT_PAuth_LR and FEAT_CPA2.

This series is based on v6.16 and probably KVM-safe but
Not tested yet:
  - nVHE boot.

Yeoreum Yun (11):
  arm64/sysreg: add system registers SCTLR2_EL2
  arm64: make SCTLR2_EL1 accessible
  arm64: initialise SCTLR2_ELx register at boot time
  arm64: cpufeature: add FEAT_SCTLR2 feature
  arm64: save/restore SCTLR2_EL1 when cpu_suspend()/resume()
  arm64: init SCTLR2_EL1 at cpu_soft_restart()
  arm64: make the per-task SCTLR2_EL1
  KVM: arm64: initialise SCTLR2_EL1 at __kvm_host_psci_cpu_entry()
  KVM: arm64: support SCTLR2_EL1 for guest
  KVM: arm64: nv: support SCTLR2_ELx on nv
  KVM: arm64: expose FEAT_SCTLR2 feature to guest

 arch/arm64/include/asm/el2_setup.h         | 14 +++++++++++-
 arch/arm64/include/asm/kvm_host.h          |  7 ++++++
 arch/arm64/include/asm/processor.h         |  5 +++++
 arch/arm64/include/asm/suspend.h           |  2 +-
 arch/arm64/include/asm/sysreg.h            | 22 ++++++++++++++++++
 arch/arm64/include/asm/vncr_mapping.h      |  1 +
 arch/arm64/kernel/cpu-reset.S              |  6 +++++
 arch/arm64/kernel/cpufeature.c             |  8 +++++++
 arch/arm64/kernel/head.S                   |  5 ++++-
 arch/arm64/kernel/process.c                |  9 ++++++++
 arch/arm64/kvm/emulate-nested.c            |  2 ++
 arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h | 16 +++++++++++++
 arch/arm64/kvm/hyp/nvhe/psci-relay.c       |  3 +++
 arch/arm64/kvm/hyp/vhe/sysreg-sr.c         |  6 +++++
 arch/arm64/kvm/nested.c                    | 13 +++++++++++
 arch/arm64/kvm/sys_regs.c                  | 25 +++++++++++++++++++--
 arch/arm64/mm/proc.S                       | 26 +++++++++++++++-------
 arch/arm64/tools/cpucaps                   |  1 +
 arch/arm64/tools/sysreg                    | 17 ++++++++++++++
 19 files changed, 175 insertions(+), 13 deletions(-)


base-commit: 038d61fd642278bab63ee8ef722c50d10ab01e8f
--
LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}

On Mon, 04 Aug 2025 13:17:13 +0100,
Yeoreum Yun <yeoreum.yun@arm.com> wrote:
> 
> This series introduces initial support for the SCTLR2_ELx registers in Linux.
> The feature is optional starting from ARMv8.8/ARMv9.3,
> and becomes mandatory from ARMv8.9/ARMv9.4.
> 
> Currently, Linux has no strict need to modify SCTLR2_ELx—
> at least assuming that firmware initializes
> these registers to reasonable defaults.
> 
> However, several upcoming architectural features will require configuring
> control bits in these registers.
> Notable examples include FEAT_PAuth_LR and FEAT_CPA2.
> 
> This series is based on v6.16 and probably KVM-safe but
> Not tested yet:
>   - nVHE boot.

"Probably" and "Not tested yet" are not exactly what we are looking
for when looking at a series that adds support for a new architectural
feature.

Also, a lot of the KVM patches are redundant now that we do have
FEAT_SCTLR2 support in KVM (see what has been merged for 6.17). You
probably want to rebase on -rc1 once it is released, which should cut
the series by half.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

Hi

> Yeoreum Yun <yeoreum.yun@arm.com> wrote:
> >
> > This series introduces initial support for the SCTLR2_ELx registers in Linux.
> > The feature is optional starting from ARMv8.8/ARMv9.3,
> > and becomes mandatory from ARMv8.9/ARMv9.4.
> >
> > Currently, Linux has no strict need to modify SCTLR2_ELx—
> > at least assuming that firmware initializes
> > these registers to reasonable defaults.
> >
> > However, several upcoming architectural features will require configuring
> > control bits in these registers.
> > Notable examples include FEAT_PAuth_LR and FEAT_CPA2.
> >
> > This series is based on v6.16 and probably KVM-safe but
> > Not tested yet:
> >   - nVHE boot.

Okay.

>
> "Probably" and "Not tested yet" are not exactly what we are looking
> for when looking at a series that adds support for a new architectural
> feature.
>
> Also, a lot of the KVM patches are redundant now that we do have
> FEAT_SCTLR2 support in KVM (see what has been merged for 6.17). You
> probably want to rebase on -rc1 once it is released, which should cut
> the series by half.
>

I didn't know that and I'll rebase on 6.17-rc1.

Thanks.

--
Sincerely,
Yeoreum Yun