On 04/05/18 17:05, Dave Martin wrote:
> The entire tail of fixup_guest_exit() is contained in if statements
> of the form if (x && *exit_code == ARM_EXCEPTION_TRAP). As a result,
> we can check just once and bail out of the function early, allowing
> the remaining if conditions to be simplified.
>
> The only awkward case is where *exit_code is changed to
> ARM_EXCEPTION_EL1_SERROR in the case of an illegal GICv2 CPU
> interface access: in that case, the GICv3 trap handling code is
> skipped using a goto. This avoids pointlessly evaluating the
> static branch check for the GICv3 case, even though we can't have
> vgic_v2_cpuif_trap and vgic_v3_cpuif_trap true simultaneously
> unless we have a GICv3 and GICv2 on the host: that sounds stupid,
> but I haven't satisfied myself that it can't happen.
Indeed, this cannot happen, unless we decided to trap access to the
memory-mapped interface of a GICv3 implementation. We don't do that.
But I guess the goto also serves a visual clue that the two cases are
mutually exclusives. Small nit below though:
>
> No functional change.
>
> Signed-off-by: Dave Martin <Dave.Martin@xxxxxxx>
> ---
> arch/arm64/kvm/hyp/switch.c | 11 +++++++----
> 1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> index 39e9166..be09c52 100644
> --- a/arch/arm64/kvm/hyp/switch.c
> +++ b/arch/arm64/kvm/hyp/switch.c
> @@ -385,11 +385,13 @@ static bool __hyp_text fixup_guest_exit(struct kvm_vcpu *vcpu, u64 *exit_code)
> * same PC once the SError has been injected, and replay the
> * trapping instruction.
> */
> - if (*exit_code == ARM_EXCEPTION_TRAP && !__populate_fault_info(vcpu))
> + if (*exit_code != ARM_EXCEPTION_TRAP)
> + goto exit;
> +
> + if (!__populate_fault_info(vcpu))
> return true;
>
> - if (static_branch_unlikely(&vgic_v2_cpuif_trap) &&
> - *exit_code == ARM_EXCEPTION_TRAP) {
> + if (static_branch_unlikely(&vgic_v2_cpuif_trap)) {
> bool valid;
>
> valid = kvm_vcpu_trap_get_class(vcpu) == ESR_ELx_EC_DABT_LOW &&
> @@ -414,12 +416,12 @@ static bool __hyp_text fixup_guest_exit(struct kvm_vcpu *vcpu, u64 *exit_code)
> if (!__skip_instr(vcpu))
> *vcpu_cpsr(vcpu) &= ~DBG_SPSR_SS;
> *exit_code = ARM_EXCEPTION_EL1_SERROR;
> + goto exit;
This goto...
> }
... should be placed here. If this was a data abort, it cannot be a
system register trap, and the below conditions cannot possibly apply.
> }
> }
>
> if (static_branch_unlikely(&vgic_v3_cpuif_trap) &&
> - *exit_code == ARM_EXCEPTION_TRAP &&
> (kvm_vcpu_trap_get_class(vcpu) == ESR_ELx_EC_SYS64 ||
> kvm_vcpu_trap_get_class(vcpu) == ESR_ELx_EC_CP15_32)) {
> int ret = __vgic_v3_perform_cpuif_access(vcpu);
> @@ -428,6 +430,7 @@ static bool __hyp_text fixup_guest_exit(struct kvm_vcpu *vcpu, u64 *exit_code)
> return true;
> }
>
> +exit:
> /* Return to the host kernel and handle the exit */
> return false;
> }
>
Thanks,
M.
--
Jazz is not dead. It just smells funny...
_______________________________________________
kvmarm mailing list
kvmarm@xxxxxxxxxxxxxxxxxxxxx
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
