KVM: arm64: Add support for FEAT

From:		Marc Zyngier <maz-AT-kernel.org>
To:		kvmarm-AT-lists.linux.dev, kvm-AT-vger.kernel.org, linux-arm-kernel-AT-lists.infradead.org
Subject:		[PATCH 0/5] KVM: arm64: Add support for FEAT_IDST
Date:		Thu, 20 Nov 2025 13:31:57 +0000
Message-ID:		<20251120133202.2037803-1-maz@kernel.org>
Cc:		Joey Gouly <joey.gouly-AT-arm.com>, Suzuki K Poulose <suzuki.poulose-AT-arm.com>, Oliver Upton <oupton-AT-kernel.org>, Zenghui Yu <yuzenghui-AT-huawei.com>
Archive-link:		Article

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.

Marc Zyngier (5):
  KVM: arm64: Add routing/handling for GMID_EL1
  KVM: arm64: Force trap of GMID_EL1 when the guest doesn't have MTE
  KVM: arm64: Add a generic synchronous exception injection primitive
  KVM: arm64: 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               |   8 ++
 arch/arm64/kvm/inject_fault.c                 |  10 +-
 arch/arm64/kvm/sys_regs.c                     |  17 ++-
 tools/testing/selftests/kvm/Makefile.kvm      |   1 +
 .../testing/selftests/kvm/arm64/idreg-idst.c  | 117 ++++++++++++++++++
 6 files changed, 149 insertions(+), 5 deletions(-)
 create mode 100644 tools/testing/selftests/kvm/arm64/idreg-idst.c

-- 
2.47.3

KVM: arm64: Add support for FEAT_IDST