linux-kernel - Re: [PATCH] KVM: PPC: Book3S HV: relax check on H_SVM_INIT

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Message-ID: <22bc6a9f-e7fd-eb24-3441-444216a38e60@linux.ibm.com>
Date:   Wed, 20 May 2020 19:35:24 +0200
From:   Laurent Dufour <ldufour@...ux.ibm.com>
To:     Greg Kurz <groug@...d.org>
Cc:     kvm-ppc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, paulus@...ba.org, mpe@...erman.id.au,
        sukadev@...ux.ibm.com, linuxram@...ibm.com
Subject: Re: [PATCH] KVM: PPC: Book3S HV: relax check on H_SVM_INIT_ABORT

Le 20/05/2020 à 19:32, Greg Kurz a écrit :
> On Wed, 20 May 2020 18:51:10 +0200
> Laurent Dufour <ldufour@...ux.ibm.com> wrote:
> 
>> The commit 8c47b6ff29e3 ("KVM: PPC: Book3S HV: Check caller of H_SVM_*
>> Hcalls") added checks of secure bit of SRR1 to filter out the Hcall
>> reserved to the Ultravisor.
>>
>> However, the Hcall H_SVM_INIT_ABORT is made by the Ultravisor passing the
>> context of the VM calling UV_ESM. This allows the Hypervisor to return to
>> the guest without going through the Ultravisor. Thus the Secure bit of SRR1
>> is not set in that particular case.
>>
>> In the case a regular VM is calling H_SVM_INIT_ABORT, this hcall will be
>> filtered out in kvmppc_h_svm_init_abort() because kvm->arch.secure_guest is
>> not set in that case.
>>
> 
> Why not checking vcpu->kvm->arch.secure_guest then ?

I don't think that's the right place.
> 
>> Fixes: 8c47b6ff29e3 ("KVM: PPC: Book3S HV: Check caller of H_SVM_* Hcalls")
>> Signed-off-by: Laurent Dufour <ldufour@...ux.ibm.com>
>> ---
>>   arch/powerpc/kvm/book3s_hv.c | 4 +---
>>   1 file changed, 1 insertion(+), 3 deletions(-)
>>
>> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
>> index 93493f0cbfe8..eb1f96cb7b72 100644
>> --- a/arch/powerpc/kvm/book3s_hv.c
>> +++ b/arch/powerpc/kvm/book3s_hv.c
>> @@ -1099,9 +1099,7 @@ int kvmppc_pseries_do_hcall(struct kvm_vcpu *vcpu)
>>   			ret = kvmppc_h_svm_init_done(vcpu->kvm);
>>   		break;
>>   	case H_SVM_INIT_ABORT:
>> -		ret = H_UNSUPPORTED;
>> -		if (kvmppc_get_srr1(vcpu) & MSR_S)
>> -			ret = kvmppc_h_svm_init_abort(vcpu->kvm);
> 
> or at least put a comment to explain why H_SVM_INIT_ABORT
> doesn't have the same sanity check as the other SVM hcalls.

I agree that might help. I'll send a v2 with a comment there.

> 
>> +		ret = kvmppc_h_svm_init_abort(vcpu->kvm);
>>   		break;
>>   
>>   	default:
>