Re: [PATCH 03/37] KVM: arm64: Move HCR_INT_OVERRIDE to default HCR_EL2 guest flag

[Marc Zyngier <marc.zyngier@xxxxxxx>]

On 12/10/17 11:41, Christoffer Dall wrote:
> From: Shih-Wei Li <shihwei@xxxxxxxxxxxxxxx>
> 
> We always set the IMO and FMO bits in the HCR_EL2 when running the
> guest, regardless if we use the vgic or not.  By moving these flags to
> HCR_GUEST_FLAGS we can avoid one of the extra save/restore operations of
> HCR_EL2 in the world switch code, and we can also soon get rid of the
> other one.
> 
> Signed-off-by: Shih-Wei Li <shihwei@xxxxxxxxxxxxxxx>
> Signed-off-by: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
> ---
>  arch/arm64/include/asm/kvm_arm.h | 4 ++--
>  arch/arm64/kvm/hyp/switch.c      | 3 ---
>  2 files changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h
> index 61d694c..e67e279 100644
> --- a/arch/arm64/include/asm/kvm_arm.h
> +++ b/arch/arm64/include/asm/kvm_arm.h
> @@ -79,9 +79,9 @@
>   */
>  #define HCR_GUEST_FLAGS (HCR_TSC | HCR_TSW | HCR_TWE | HCR_TWI | HCR_VM | \
>  			 HCR_TVM | HCR_BSU_IS | HCR_FB | HCR_TAC | \
> -			 HCR_AMO | HCR_SWIO | HCR_TIDCP | HCR_RW)
> +			 HCR_AMO | HCR_SWIO | HCR_TIDCP | HCR_RW | \
> +			 HCR_FMO | HCR_IMO)
>  #define HCR_VIRT_EXCP_MASK (HCR_VSE | HCR_VI | HCR_VF)
> -#define HCR_INT_OVERRIDE   (HCR_FMO | HCR_IMO)
>  #define HCR_HOST_VHE_FLAGS (HCR_RW | HCR_TGE | HCR_E2H)
>  
>  /* TCR_EL2 Registers bits */
> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> index a50ddf3..bcf1a79 100644
> --- a/arch/arm64/kvm/hyp/switch.c
> +++ b/arch/arm64/kvm/hyp/switch.c
> @@ -164,8 +164,6 @@ static void __hyp_text __vgic_save_state(struct kvm_vcpu *vcpu)
>  		__vgic_v3_save_state(vcpu);
>  	else
>  		__vgic_v2_save_state(vcpu);
> -
> -	write_sysreg(read_sysreg(hcr_el2) & ~HCR_INT_OVERRIDE, hcr_el2);
>  }
>  
>  static void __hyp_text __vgic_restore_state(struct kvm_vcpu *vcpu)
> @@ -173,7 +171,6 @@ static void __hyp_text __vgic_restore_state(struct kvm_vcpu *vcpu)
>  	u64 val;
>  
>  	val = read_sysreg(hcr_el2);
> -	val |= 	HCR_INT_OVERRIDE;
>  	val |= vcpu->arch.irq_lines;
>  	write_sysreg(val, hcr_el2);
>  
> 

To expand on why this is actually safe: IMO/FMO control both taking the
interrupts to EL2 and remapping ICC_*_EL1 to ICV_*_EL1 executed at EL1.
As long as we ensure that these bits are clear when returning to the EL1
host, we're OK.

Reviewed-by: Marc Zyngier <marc.zyngier@xxxxxxx>

	M.
-- 
Jazz is not dead. It just smells funny...