[PATCH v2 2/2] KVM: arm64: Move FGT value configuration to vCPU state

[Will Deacon]

On Thu, Mar 23, 2023 at 03:48:36PM +0000, Mark Brown wrote:
> Currently the only fine grained traps we use are the SME ones and we decide
> if we want to manage fine grained traps for the guest and which to
> enable based on the presence of that feature. In order to support SME,
> PIE and other features where we need fine grained traps we will need to
> select per guest which traps are enabled. Move to storing the traps to
> enable in the vCPU data, updating the registers if fine grained traps
> are supported and any are enabled. In order to ensure that the fine
> grained traps are restored along with other traps there is a bit of
> asymmetry with where the registers are restored on guest exit.
> 
> Currently we always set this register to 0 when running the guest so
> unconditionally use that value for guests, future patches will configure
> this.
> 
> No functional change, though we will do additional saves of the guest
> FGT register configurations and will save and restore even if the host
> and guest states are identical.
> 
> Signed-off-by: Mark Brown <broonie at kernel.org>
> ---
>  arch/arm64/include/asm/kvm_emulate.h       | 16 ++++++++++++++
>  arch/arm64/include/asm/kvm_host.h          |  2 ++
>  arch/arm64/kvm/arm.c                       |  1 +
>  arch/arm64/kvm/hyp/include/hyp/switch.h    | 35 ++++++++++++++++--------------
>  arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h |  9 ++++++++
>  5 files changed, 47 insertions(+), 16 deletions(-)

[...]

> diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h
> index 07d37ff88a3f..bf0183a3a82d 100644
> --- a/arch/arm64/kvm/hyp/include/hyp/switch.h
> +++ b/arch/arm64/kvm/hyp/include/hyp/switch.h
> @@ -88,33 +88,36 @@ static inline void __activate_traps_common(struct kvm_vcpu *vcpu)
>  	vcpu->arch.mdcr_el2_host = read_sysreg(mdcr_el2);
>  	write_sysreg(vcpu->arch.mdcr_el2, mdcr_el2);
>  
> -	if (cpus_have_final_cap(ARM64_SME)) {
> -		sysreg_clear_set_s(SYS_HFGRTR_EL2,
> -				   HFGxTR_EL2_nSMPRI_EL1_MASK |
> -				   HFGxTR_EL2_nTPIDR2_EL0_MASK,
> -				   0);
> -		sysreg_clear_set_s(SYS_HFGWTR_EL2,
> -				   HFGxTR_EL2_nSMPRI_EL1_MASK |
> -				   HFGxTR_EL2_nTPIDR2_EL0_MASK,
> -				   0);
> +	if (cpus_have_final_cap(ARM64_HAS_FGT)) {
> +		write_sysreg_s(__vcpu_sys_reg(vcpu, HFGRTR_EL2),
> +			       SYS_HFGRTR_EL2);
> +
> +		write_sysreg_s(__vcpu_sys_reg(vcpu, HFGWTR_EL2),
> +			       SYS_HFGWTR_EL2);
>  	}
>  }
>  
>  static inline void __deactivate_traps_common(struct kvm_vcpu *vcpu)
>  {
> +	struct kvm_cpu_context *host_ctxt;
> +
>  	write_sysreg(vcpu->arch.mdcr_el2_host, mdcr_el2);
>  
>  	write_sysreg(0, hstr_el2);
>  	if (kvm_arm_support_pmu_v3())
>  		write_sysreg(0, pmuserenr_el0);
>  
> -	if (cpus_have_final_cap(ARM64_SME)) {
> -		sysreg_clear_set_s(SYS_HFGRTR_EL2, 0,
> -				   HFGxTR_EL2_nSMPRI_EL1_MASK |
> -				   HFGxTR_EL2_nTPIDR2_EL0_MASK);
> -		sysreg_clear_set_s(SYS_HFGWTR_EL2, 0,
> -				   HFGxTR_EL2_nSMPRI_EL1_MASK |
> -				   HFGxTR_EL2_nTPIDR2_EL0_MASK);
> +	/*
> +	 * Restore the host FGT configuration here since it's managing
> +	 * traps.
> +	 */
> +	if (cpus_have_final_cap(ARM64_HAS_FGT)) {
> +		host_ctxt = &this_cpu_ptr(&kvm_host_data)->host_ctxt;
> +
> +		write_sysreg_s(__vcpu_sys_reg(vcpu, HFGRTR_EL2),
> +			       SYS_HFGRTR_EL2);
> +		write_sysreg_s(__vcpu_sys_reg(vcpu, HFGWTR_EL2),
> +			       SYS_HFGWTR_EL2);

I don't understand this hunk. Where is `host_ctxt` being used?

Will