[PATCH v4 27/28] KVM: arm64: Move HCRX_EL2 switch to load/put on VHE systems

[Jing Zhang]

Hi Marc,

On Tue, Aug 15, 2023 at 11:47 AM Marc Zyngier <maz at kernel.org> wrote:
>
> Although the nVHE behaviour requires HCRX_EL2 to be switched
> on each switch between host and guest, there is nothing in
> this register that would affect a VHE host.
>
> It is thus possible to save/restore this register on load/put
> on VHE systems, avoiding unnecessary sysreg access on the hot
> path. Additionally, it avoids unnecessary traps when running
> with NV.
>
> To achieve this, simply move the read/writes to the *_common()
> helpers, which are called on load/put on VHE, and more eagerly
> on nVHE.
>
> Reviewed-by: Eric Auger <eric.auger at redhat.com>
> Signed-off-by: Marc Zyngier <maz at kernel.org>
> ---
>  arch/arm64/kvm/hyp/include/hyp/switch.h | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h
> index a4750070563f..060c5a0409e5 100644
> --- a/arch/arm64/kvm/hyp/include/hyp/switch.h
> +++ b/arch/arm64/kvm/hyp/include/hyp/switch.h
> @@ -197,6 +197,9 @@ 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_HAS_HCX))
> +               write_sysreg_s(HCRX_GUEST_FLAGS, SYS_HCRX_EL2);
> +
>         __activate_traps_hfgxtr(vcpu);
>  }
>
> @@ -213,6 +216,9 @@ static inline void __deactivate_traps_common(struct kvm_vcpu *vcpu)
>                 vcpu_clear_flag(vcpu, PMUSERENR_ON_CPU);
>         }
>
> +       if (cpus_have_final_cap(ARM64_HAS_HCX))
> +               write_sysreg_s(HCRX_HOST_FLAGS, SYS_HCRX_EL2);
> +
>         __deactivate_traps_hfgxtr(vcpu);
>  }
>
> @@ -227,9 +233,6 @@ static inline void ___activate_traps(struct kvm_vcpu *vcpu)
>
>         if (cpus_have_final_cap(ARM64_HAS_RAS_EXTN) && (hcr & HCR_VSE))
>                 write_sysreg_s(vcpu->arch.vsesr_el2, SYS_VSESR_EL2);
> -
> -       if (cpus_have_final_cap(ARM64_HAS_HCX))
> -               write_sysreg_s(HCRX_GUEST_FLAGS, SYS_HCRX_EL2);
>  }
>
>  static inline void ___deactivate_traps(struct kvm_vcpu *vcpu)
> @@ -244,9 +247,6 @@ static inline void ___deactivate_traps(struct kvm_vcpu *vcpu)
>                 vcpu->arch.hcr_el2 &= ~HCR_VSE;
>                 vcpu->arch.hcr_el2 |= read_sysreg(hcr_el2) & HCR_VSE;
>         }
> -
> -       if (cpus_have_final_cap(ARM64_HAS_HCX))
> -               write_sysreg_s(HCRX_HOST_FLAGS, SYS_HCRX_EL2);
>  }
>
>  static inline bool __populate_fault_info(struct kvm_vcpu *vcpu)
> --
> 2.34.1
>

Reviewed-by: Jing Zhang <jingzhangos at google.com>

Jing