Re: [PATCH v3 0/3] KVM: arm64: ID register finalisation fixes

[Lorenzo Stoakes (ARM)]

On Tue, Sep 01, 2026 at 07:18:47PM +0100, Mark Brown wrote:
> While looking at some feature enablement I noticed that there are some
> scenarios where we can end up with an inconsistently configured vCPU due
> to finalizing configuration based on ID registers before we have blocked
> writes to the ID registers. This series aims to clean up these issues.
>
> Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>

Ran the 3/3 test locally and confirmed the test fails without 2/3, passes
with it.

Also got our AI overloads to test 1/3 locally by flipping
ID_AA64PFR0_EL1.GIC after vGIC creation:

Before:
	GIC field after vGIC create: 1
	GIC field after userspace write: 0
	GIC field after first run:     1
	HFGRTR_EL2 written 0000008000000000 read back 0000000000000000
	RESULT: FAIL - ICC_IGRPENn_EL1 forced RES0 (NV masks computed with GIC=0)

After:
	GIC field after vGIC create: 1
	GIC field after userspace write: 0
	GIC field after first run:     1
	HFGRTR_EL2 written 0000008000000000 read back 0000008000000000
	RESULT: PASS - ICC_IGRPENn_EL1 writable (NV masks match GIC=IMP)

So for the whole series:

Tested-by: Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx>

> ---
> Changes in v3:
> - Rebase onto v7.3-rc1.
> - Explain why KVM_ARCH_FLAG_ID_REGS_INITIALIZED is not reused.
> - Pull in Fuad's test cases.
> - Link to v2: https://patch.msgid.link/20260803-kvm-arm64-idreg-final-v2-0-d7d7e4efc640@xxxxxxxxxx
>
> Changes in v2:
> - Also replace the kvm_vm_has_ran_once() usage in kvm_set_vm_id_rg() and
>   kvm_vm_finalize_sys_regs() with kvm_id_regs_final().
> - Link to v1: https://patch.msgid.link/20260731-kvm-arm64-idreg-final-v1-0-3de2a5616dc6@xxxxxxxxxx
>
> ---
> Fuad Tabba (1):
>       KVM: arm64: selftests: Check ID regs are immutable after a failed run
>
> Mark Brown (2):
>       KVM: arm64: Finalize guest-wide sysregs prior to per-vCPU sysregs
>       KVM: arm64: Block ID register changes after we rely on the values
>
>  arch/arm64/include/asm/kvm_host.h               |   8 ++
>  arch/arm64/kvm/arm.c                            |   2 +-
>  arch/arm64/kvm/sys_regs.c                       |  57 ++++++++-----
>  arch/arm64/kvm/sys_regs.h                       |   2 +-
>  arch/arm64/kvm/vgic/vgic-init.c                 |   6 +-
>  tools/testing/selftests/kvm/arm64/set_id_regs.c | 106 +++++++++++++++++++++++-
>  6 files changed, 153 insertions(+), 28 deletions(-)
> ---
> base-commit: cee9395acd8043be0644b25c34bfa86623f2b935
> change-id: 20260729-kvm-arm64-idreg-final-77cbc46b558a
>
> Best regards,
> --
> Mark Brown <broonie@xxxxxxxxxx>
>
>

--
Cheers, Lorenzo