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

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Message-Id: <f6a71da6-6363-8cba-8215-78b23a046443@linux.ibm.com>
Date:   Fri, 20 Mar 2020 15:36:05 +0100
From:   Laurent Dufour <ldufour@...ux.ibm.com>
To:     bharata@...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

Le 20/03/2020 à 12:24, Bharata B Rao a écrit :
> 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?

I checked that and didn't find any issue there.

My only concern was that block:
	kvm_for_each_vcpu(i, vcpu, kvm) {
		spin_lock(&vcpu->arch.vpa_update_lock);
		unpin_vpa_reset(kvm, &vcpu->arch.dtl);
		unpin_vpa_reset(kvm, &vcpu->arch.slb_shadow);
		unpin_vpa_reset(kvm, &vcpu->arch.vpa);
		spin_unlock(&vcpu->arch.vpa_update_lock);
	}

But that seems to be safe.

However I'm not a familiar with the KVM's code, do you think an additional 
KVMPPC_SECURE_INIT_* value needed here?

Thanks,
Laurent.