[RFC PATCH 0/4] KVM: arm64: vcpu sysreg accessor rework

[Marc Zyngier <maz@kernel.org>]

As a follow-up to this series[1] fixing bugs around the RESx
behaviours, here's another that tries to bring some additional sanity
to the way the RESx masks are applied.

Currently, we have *one* accessor (__vcpu_sys_reg()) that can either
be used as a rvalue or lvalue while that applies the RESx masks behind
the scenes.

However, when used as a lvalue, it does the wrong thing, as it only
sanitises the value we're about to overwrite. This is pointless work
and potentially hides bugs.

Instead, I propose that we move to a set of store-specific accessors
(for assignments and RMW) instead of the lvalue hack. This then allows
the legacy accessor to be converted to rvalue-only.

Note that these patches are on top of the NV series, so not suitable
for the current set of upstream. But assuming I'm getting positive
feedback, I'm happy to rebase that on something less bleeding edge.

Thanks,

	M.

[1] https://lore.kernel.org/r/20250112165029.1181056-1-maz@kernel.org

Marc Zyngier (4):
  KVM: arm64: Add assignment-specific sysreg accessor
  KVM: arm64: Add RMW specific sysreg accessor
  KVM: arm64: Don't use __vcpu_sys_reg() to get the address of a sysreg
  KVM: arm64: Make __vcpu_sys_reg() a pure rvalue operand

 arch/arm64/include/asm/kvm_host.h          | 31 ++++++++++--
 arch/arm64/kvm/arch_timer.c                | 20 ++++----
 arch/arm64/kvm/debug.c                     |  4 +-
 arch/arm64/kvm/fpsimd.c                    |  6 +--
 arch/arm64/kvm/hyp/exception.c             |  4 +-
 arch/arm64/kvm/hyp/include/hyp/switch.h    |  2 +-
 arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h |  6 +--
 arch/arm64/kvm/hyp/nvhe/hyp-main.c         |  4 +-
 arch/arm64/kvm/hyp/vhe/switch.c            |  4 +-
 arch/arm64/kvm/hyp/vhe/sysreg-sr.c         | 48 +++++++++---------
 arch/arm64/kvm/nested.c                    |  2 +-
 arch/arm64/kvm/pmu-emul.c                  | 20 ++++----
 arch/arm64/kvm/sys_regs.c                  | 58 +++++++++++-----------
 arch/arm64/kvm/sys_regs.h                  |  4 +-
 arch/arm64/kvm/vgic/vgic-v3-nested.c       | 10 ++--
 15 files changed, 123 insertions(+), 100 deletions(-)

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2.39.2