Re: [PATCH v10 6/7] x86/kvm/hyper-v: Add support for synthetic debugger via hypercalls

[Vitaly Kuznetsov <vkuznets@redhat.com>]

Jon Doron <arilou@gmail.com> writes:

> There is another mode for the synthetic debugger which uses hypercalls
> to send/recv network data instead of the MSR interface.
>
> This interface is much slower and less recommended since you might get
> a lot of VMExits while KDVM polling for new packets to recv, rather
> than simply checking the pending page to see if there is data avialble
> and then request.
>
> Signed-off-by: Jon Doron <arilou@gmail.com>
> ---
>  arch/x86/kvm/hyperv.c | 28 ++++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
>
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index 59c6eadb7eca..45ff3098e079 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -1832,6 +1832,34 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
>  		}
>  		ret = kvm_hv_send_ipi(vcpu, ingpa, outgpa, true, false);
>  		break;
> +	case HVCALL_POST_DEBUG_DATA:
> +	case HVCALL_RETRIEVE_DEBUG_DATA:
> +		if (unlikely(fast)) {
> +			ret = HV_STATUS_INVALID_PARAMETER;
> +			break;
> +		}
> +		fallthrough;
> +	case HVCALL_RESET_DEBUG_SESSION: {
> +		struct kvm_hv_syndbg *syndbg = vcpu_to_hv_syndbg(vcpu);
> +
> +		if (!syndbg->active) {
> +			ret = HV_STATUS_INVALID_HYPERCALL_CODE;
> +			break;
> +		}
> +
> +		if (!(syndbg->options & HV_X64_SYNDBG_OPTION_USE_HCALLS)) {
> +			ret = HV_STATUS_OPERATION_DENIED;
> +			break;
> +		}
> +		vcpu->run->exit_reason = KVM_EXIT_HYPERV;
> +		vcpu->run->hyperv.type = KVM_EXIT_HYPERV_HCALL;
> +		vcpu->run->hyperv.u.hcall.input = param;
> +		vcpu->run->hyperv.u.hcall.params[0] = ingpa;
> +		vcpu->run->hyperv.u.hcall.params[1] = outgpa;
> +		vcpu->arch.complete_userspace_io =
> +				kvm_hv_hypercall_complete_userspace;

We may want to split this into a helper in the future (as
HVCALL_POST_MESSAGE handling is not any different - basically, we just
pass the full hypercall input to the userspace, regardless of what the
hypercall was).

> +		return 0;
> +	}
>  	default:
>  		ret = HV_STATUS_INVALID_HYPERCALL_CODE;
>  		break;

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>

-- 
Vitaly