[PATCH v4 0/9] KVM: arm64: Add support for FEAT_IDST

[Marc Zyngier <maz@kernel.org>]

FEAT_IDST appeared in ARMv8.4, and allows ID registers to be trapped
if they are not implemented. This only concerns 3 registers (GMID_EL1,
CCSIDR2_EL1 and SMIDR_EL1), which are part of features that may not be
exposed to the guest even if present on the host.

For these registers, the HW should report them with EC=0x18, even if
the feature isn't implemented.

Add support for this feature by handling these registers in a specific
way and implementing GMID_EL1 support in the process. A very basic
selftest checks that these registers behave as expected.

* From v3: [3]

  - Added ID_AA64MMFR2_EL1.IDS == EL3 (Ben)

  - Introduced in_feat_id_space() helper (Yao)

  - Collected RBs, with thanks

* From v2: [2]

  - Repainted ID_AA64MMFR2_EL1.IDS description (Oliver)

  - Made the IDST handling more generic in the core KVM code, which
    resulted in the series being restructured a bit

  - Added handling to pKVM (in a slightly different way, as pKVM
    insist on seeing a full enumeration of the trapped registers)

  - Some cleanups

  - Collected RBs, with thanks

* From v1: [1]

  - Fixed commit message in patch #4 (Ben)

  - Collected RB, with thanks (Joey)

[1] https://lore.kernel.org/r/20251120133202.2037803-1-maz@kernel.org
[2] https://lore.kernel.org/r/20251126155951.1146317-1-maz@kernel.org
[3] https://lore.kernel.org/r/20251204094806.3846619-1-maz@kernel.org

Marc Zyngier (9):
  arm64: Repaint ID_AA64MMFR2_EL1.IDS description
  KVM: arm64: Add trap routing for GMID_EL1
  KVM: arm64: Add a generic synchronous exception injection primitive
  KVM: arm64: Handle FEAT_IDST for sysregs without specific handlers
  KVM: arm64: Handle CSSIDR2_EL1 and SMIDR_EL1 in a generic way
  KVM: arm64: Force trap of GMID_EL1 when the guest doesn't have MTE
  KVM: arm64: pkvm: Add a generic synchronous exception injection
    primitive
  KVM: arm64: pkvm: Report optional ID register traps with a 0x18
    syndrome
  KVM: arm64: selftests: Add a test for FEAT_IDST

 arch/arm64/include/asm/kvm_emulate.h          |   1 +
 arch/arm64/kvm/emulate-nested.c               |  21 ++++
 arch/arm64/kvm/hyp/nvhe/sys_regs.c            |  39 ++++--
 arch/arm64/kvm/inject_fault.c                 |  10 +-
 arch/arm64/kvm/sys_regs.c                     |   4 +-
 arch/arm64/kvm/sys_regs.h                     |  10 ++
 arch/arm64/tools/sysreg                       |   7 +-
 tools/testing/selftests/kvm/Makefile.kvm      |   1 +
 .../testing/selftests/kvm/arm64/idreg-idst.c  | 117 ++++++++++++++++++
 9 files changed, 194 insertions(+), 16 deletions(-)
 create mode 100644 tools/testing/selftests/kvm/arm64/idreg-idst.c

-- 
2.47.3