Re: [PATCH 1/5] KVM: arm64: Correctly honor the presence of FEAT_TCRX

Joey Gouly
2024-06-25T14:37:40Z

On Tue, Jun 25, 2024 at 02:00:37PM +0100, Marc Zyngier wrote:
> We currently blindly enable TCR2_EL1 use in a guest, irrespective
> of the feature set. This is obviously wrong, and we should actually
> honor the guest configuration and handle the possible trap resulting
> from the guest being buggy.
>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
> arch/arm64/include/asm/kvm_arm.h | 2 +-
> arch/arm64/kvm/sys_regs.c | 9 +++++++++
> 2 files changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h
> index b2adc2c6c82a5..e6682a3ace5af 100644
> --- a/arch/arm64/include/asm/kvm_arm.h
> +++ b/arch/arm64/include/asm/kvm_arm.h
> @@ -102,7 +102,7 @@
> #define HCR_HOST_NVHE_PROTECTED_FLAGS (HCR_HOST_NVHE_FLAGS | HCR_TSC)
> #define HCR_HOST_VHE_FLAGS (HCR_RW | HCR_TGE | HCR_E2H)
>
> -#define HCRX_GUEST_FLAGS (HCRX_EL2_SMPME | HCRX_EL2_TCR2En)
> +#define HCRX_GUEST_FLAGS (HCRX_EL2_SMPME)
> #define HCRX_HOST_FLAGS (HCRX_EL2_MSCEn | HCRX_EL2_TCR2En | HCRX_EL2_EnFPM)
>
> /* TCR_EL2 Registers bits */
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 22b45a15d0688..71996d36f3751 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -383,6 +383,12 @@ static bool access_vm_reg(struct kvm_vcpu *vcpu,
> bool was_enabled = vcpu_has_cache_enabled(vcpu);
> u64 val, mask, shift;
>
> + if (reg_to_encoding(r) == SYS_TCR2_EL1 &&
> + !kvm_has_feat(vcpu->kvm, ID_AA64MMFR3_EL1, TCRX, IMP)) {
> + kvm_inject_undefined(vcpu);
> + return false;
> + }
> +

If we need to start doing this with more vm(sa) registers, it might make sense
to think of a way to do this without putting a big if/else in here. For now
this is seems fine.

> BUG_ON(!p->is_write);
>
> get_access_mask(r, &mask, &shift);
> @@ -4060,6 +4066,9 @@ void kvm_init_sysreg(struct kvm_vcpu *vcpu)
>
> if (kvm_has_feat(kvm, ID_AA64ISAR2_EL1, MOPS, IMP))
> vcpu->arch.hcrx_el2 |= (HCRX_EL2_MSCEn | HCRX_EL2_MCE2);
> +
> + if (kvm_has_feat(kvm, ID_AA64MMFR3_EL1, TCRX, IMP))
> + vcpu->arch.hcrx_el2 |= HCRX_EL2_TCR2En;
> }
>
> if (test_bit(KVM_ARCH_FLAG_FGU_INITIALIZED, &kvm->arch.flags))

Reviewed-by: Joey Gouly <joey.gouly@arm.com>