[PATCH 21/25] KVM: arm64: Make TLBI OS/Range UNDEF if not advertised to the guest

[Joey Gouly]

Question,

On Mon, Jan 22, 2024 at 08:18:48PM +0000, Marc Zyngier wrote:
> Outer Shareable and Range TLBI instructions shouldn't be made available
> to the guest if they are not advertised. Use FGU to disable those,
> and set HCR_EL2.TLBIOS in the case the host doesn't have FGT.
> 
> Signed-off-by: Marc Zyngier <maz at kernel.org>
> ---
>  arch/arm64/kvm/sys_regs.c | 29 +++++++++++++++++++++++++++++
>  1 file changed, 29 insertions(+)
> 
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index a62efd8a2959..3c939ea4a28f 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -3949,6 +3949,9 @@ void kvm_init_sysreg(struct kvm_vcpu *vcpu)
>  
>  	mutex_lock(&kvm->arch.config_lock);
>  
> +	if (!kvm_has_feat(kvm, ID_AA64ISAR0_EL1, TLB, OS))
> +		vcpu->arch.hcr_el2 |= HCR_TTLBOS;
> +
>  	if (test_bit(KVM_ARCH_FLAG_FGU_INITIALIZED, &kvm->arch.flags))
>  		goto out;
>  
> @@ -3961,6 +3964,32 @@ void kvm_init_sysreg(struct kvm_vcpu *vcpu)
>  				       HFGxTR_EL2_nSMPRI_EL1_MASK	|
>  				       HFGxTR_EL2_nTPIDR2_EL0_MASK);
>  
> +	if (!kvm_has_feat(kvm, ID_AA64ISAR0_EL1, TLB, OS))
> +		kvm->arch.fgu[HFGITR_GROUP] |= (HFGITR_EL2_TLBIRVAALE1OS|
> +						HFGITR_EL2_TLBIRVALE1OS	|
> +						HFGITR_EL2_TLBIRVAAE1OS	|
> +						HFGITR_EL2_TLBIRVAE1OS	|
> +						HFGITR_EL2_TLBIVAALE1OS	|
> +						HFGITR_EL2_TLBIVALE1OS	|
> +						HFGITR_EL2_TLBIVAAE1OS	|
> +						HFGITR_EL2_TLBIASIDE1OS	|
> +						HFGITR_EL2_TLBIVAE1OS	|
> +						HFGITR_EL2_TLBIVMALLE1OS);
> +
> +	if (!kvm_has_feat(kvm, ID_AA64ISAR0_EL1, TLB, RANGE))
> +		kvm->arch.fgu[HFGITR_GROUP] |= (HFGITR_EL2_TLBIRVAALE1	|
> +						HFGITR_EL2_TLBIRVALE1	|
> +						HFGITR_EL2_TLBIRVAAE1	|
> +						HFGITR_EL2_TLBIRVAE1	|
> +						HFGITR_EL2_TLBIRVAALE1IS|
> +						HFGITR_EL2_TLBIRVALE1IS	|
> +						HFGITR_EL2_TLBIRVAAE1IS	|
> +						HFGITR_EL2_TLBIRVAE1IS	|
> +						HFGITR_EL2_TLBIRVAALE1OS|
> +						HFGITR_EL2_TLBIRVALE1OS	|
> +						HFGITR_EL2_TLBIRVAAE1OS	|
> +						HFGITR_EL2_TLBIRVAE1OS);
> +
>  	set_bit(KVM_ARCH_FLAG_FGU_INITIALIZED, &kvm->arch.flags);
>  out:
>  	mutex_unlock(&kvm->arch.config_lock);

I think I'm right in saying..

If the VM is running on a platform with ID_AA64ISAR0_EL1.TLB=0b010 (Outer
Shareable and TLB range maintenance instructions are implemented.) but without
support for FEAT_FGT, and the VMM sets the ID reg to ID_AA64ISAR0_EL1.TLB=0,
this change will trap the TLBI *OS instructions but not the following: 

    TLBI RVAAE1
    TLBI RVAAE1IS
    TLBI RVAALE1
    TLBI RVAALE1IS
    TLBI RVAE1
    TLBI RVAE1IS
    TLBI RVALE1
    TLBI RVALE1IS

These TLB range instructions only trap with HCR_EL2.TTLB, however that traps
all TLB instructions. You may have left this off intentionally, if so can you
add something to the commit message.

Thanks,
Joey