[PATCH v2 0/4] KVM: arm64: vcpu sysreg accessor rework

[Marc Zyngier <maz@kernel.org>]

This series tries to bring some sanity to the way the RESx masks
are applied when accessing the in-memory view of the guest's
system registers.

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. This works fine when used as a rvalue.

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.

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

Given the level of churn this introduces, I'd like this to land very
early in the cycle. Either before 6.16-rc2, or early in 6.17.

* From v1 [1]

  - rebased to kvmarm-fixes-6.16-1

[1] https://lore.kernel.org/all/20250113183524.1378778-1-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                | 18 +++----
 arch/arm64/kvm/debug.c                     |  4 +-
 arch/arm64/kvm/fpsimd.c                    |  4 +-
 arch/arm64/kvm/hyp/exception.c             |  4 +-
 arch/arm64/kvm/hyp/include/hyp/switch.h    |  4 +-
 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                  | 24 ++++-----
 arch/arm64/kvm/sys_regs.c                  | 60 +++++++++++-----------
 arch/arm64/kvm/sys_regs.h                  |  4 +-
 arch/arm64/kvm/vgic/vgic-v3-nested.c       | 10 ++--
 15 files changed, 125 insertions(+), 102 deletions(-)

-- 
2.39.2