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SubjectRe: [PATCH 2/2] KVM: PPC: Book3S HV: H_SVM_INIT_START must call UV_RETURN
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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@linux.ibm.com>
>> Cc: Paul Mackerras <paulus@ozlabs.org>
>> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
>> Cc: Michael Ellerman <mpe@ellerman.id.au>
>> Signed-off-by: Laurent Dufour <ldufour@linux.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.




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