[v3] initialize SCTRL2_ELx

[PATCH v3 0/5] initialize SCTRL2_ELx

Posted by Yeoreum Yun 1 month, 3 weeks ago

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.

Patch History
==============
from v2 to v3:
  - rewrite commit messages.
  - fix missing SCTLR2_EL2 synchonization at boot.
  - https://lore.kernel.org/all/20250811163340.1561893-1-yeoreum.yun@arm.com/

from v1 to v2:
  - rebase to v6.17-rc1
  - https://lore.kernel.org/all/20250804121724.3681531-1-yeoreum.yun@arm.com/

Yeoreum Yun (5):
  arm64: make SCTLR2_EL1 accessible
  arm64: initialise SCTLR2_ELx register at boot time
  arm64: save/restore SCTLR2_EL1 when cpu_suspend()/resume()
  arm64: initialise SCTLR2_EL1 at cpu_soft_restart()
  arm64: make the per-task SCTLR2_EL1

 arch/arm64/include/asm/assembler.h   | 22 ++++++++++++++++++++++
 arch/arm64/include/asm/el2_setup.h   | 14 +++++++++++++-
 arch/arm64/include/asm/processor.h   |  5 +++++
 arch/arm64/include/asm/suspend.h     |  2 +-
 arch/arm64/include/asm/sysreg.h      |  5 +++++
 arch/arm64/kernel/cpu-reset.S        |  6 ++++++
 arch/arm64/kernel/head.S             |  5 +++++
 arch/arm64/kernel/hyp-stub.S         | 10 ++++++++++
 arch/arm64/kernel/process.c          |  9 +++++++++
 arch/arm64/kvm/hyp/nvhe/psci-relay.c |  3 +++
 arch/arm64/mm/proc.S                 | 26 ++++++++++++++++++--------
 11 files changed, 97 insertions(+), 10 deletions(-)


base-commit: 8f5ae30d69d7543eee0d70083daf4de8fe15d585
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LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}

Re: [PATCH v3 0/5] initialize SCTRL2_ELx

Posted by Dave Martin 1 month, 2 weeks ago

Hi,

On Wed, Aug 13, 2025 at 01:01:13PM +0100, Yeoreum Yun 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 looks OK overall to me, apart from some confusion between
SCTLR_ELx and SCTLR2_ELx in patch 2 (see my comments there).

This code will need to be tested somehow.  Do you have any thoughts on
this?  Hacking the bootwrapper, KVM and/or kvmtool may provide a way of
checking what happens when the kernel is entered with "wrong" initial
values in relevant bits (HRCX_EL2.SCTLR2En, SCTLR2_EL{1,2}).

Regarding the patch history:

> Patch History
> ==============
> from v2 to v3:
>   - rewrite commit messages.
>   - fix missing SCTLR2_EL2 synchonization at boot.
>   - https://lore.kernel.org/all/20250811163340.1561893-1-yeoreum.yun@arm.com/
> 
> from v1 to v2:
>   - rebase to v6.17-rc1
>   - https://lore.kernel.org/all/20250804121724.3681531-1-yeoreum.yun@arm.com/

Going forwards, can you try to make sure that significant changes to
the series are all mentioned here?

I didn't have time to look at v2, and in the meantime half of the
series disappeared and a chunk of code was moved from one patch to
another.  I saves reviewers some time and effort if they do not have to
dig through previous review conversations in order to understand what
changed between versions of a series.

(No need to mention every trivial change, though.)

Cheers
---Dave