linux-kernel - Re: [PATCH 2/2] KVM: PPC: Book3S HV: H_SVM_INIT_START must call UV

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Date:   Mon, 23 Mar 2020 11:09:33 -0300
From:   Fabiano Rosas <farosas@...ux.ibm.com>
To:     Laurent Dufour <ldufour@...ux.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        kvm-ppc@...r.kernel.org
Cc:     Bharata B Rao <bharata@...ux.ibm.com>,
        Paul Mackerras <paulus@...abs.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH 2/2] KVM: PPC: Book3S HV: H_SVM_INIT_START must call UV_RETURN

Laurent Dufour <ldufour@...ux.ibm.com> writes:

> When the call to UV_REGISTER_MEM_SLOT is failing, for instance because
> there is not enough free secured memory, the Hypervisor (HV) has to call
> UV_RETURN to report the error to the Ultravisor (UV). Then the UV will call
> H_SVM_INIT_ABORT to abort the securing phase and go back to the calling VM.
>
> If the kvm->arch.secure_guest is not set, in the return path rfid is called
> but there is no valid context to get back to the SVM since the Hcall has
> been routed by the Ultravisor.
>
> Move the setting of kvm->arch.secure_guest earlier in
> kvmppc_h_svm_init_start() so in the return path, UV_RETURN will be called
> instead of rfid.
>
> Cc: Bharata B Rao <bharata@...ux.ibm.com>
> Cc: Paul Mackerras <paulus@...abs.org>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Signed-off-by: Laurent Dufour <ldufour@...ux.ibm.com>
> ---

I tested this along with the code that rejects the secure transition
when it is not enabled in KVM.

I have also forced a KVM_PPC_SVM_OFF (via system_reset) right after
setting kvm->arch.secure_guest and nothing bad happened.

Tested-by: Fabiano Rosas <farosas@...ux.ibm.com>


>  arch/powerpc/kvm/book3s_hv_uvmem.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c
> index 79b1202b1c62..68dff151315c 100644
> --- a/arch/powerpc/kvm/book3s_hv_uvmem.c
> +++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
> @@ -209,6 +209,8 @@ unsigned long kvmppc_h_svm_init_start(struct kvm *kvm)
>  	int ret = H_SUCCESS;
>  	int srcu_idx;
>
> +	kvm->arch.secure_guest = KVMPPC_SECURE_INIT_START;
> +
>  	if (!kvmppc_uvmem_bitmap)
>  		return H_UNSUPPORTED;
>
> @@ -233,7 +235,6 @@ unsigned long kvmppc_h_svm_init_start(struct kvm *kvm)
>  			goto out;
>  		}
>  	}
> -	kvm->arch.secure_guest |= KVMPPC_SECURE_INIT_START;
>  out:
>  	srcu_read_unlock(&kvm->srcu, srcu_idx);
>  	return ret;