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

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Date:   Fri, 20 Mar 2020 16:54:03 +0530
From:   Bharata B Rao <bharata@...ux.ibm.com>
To:     Laurent Dufour <ldufour@...ux.ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        kvm-ppc@...r.kernel.org, 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

On Fri, Mar 20, 2020 at 11:26:43AM +0100, Laurent Dufour wrote:
> 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>
> ---
>  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;

There is an assumption that memory slots would have been registered with UV
if KVMPPC_SECURE_INIT_START has been done. KVM_PPC_SVM_OFF ioctl will skip
unregistration and other steps during reboot if KVMPPC_SECURE_INIT_START
hasn't been done.

Have you checked if that path isn't affected by this change?

Regards,
Bharata.