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Date: Tue, 12 Nov 2019 22:32:33 -0800
From: Ram Pai <linuxram@us.ibm.com>
To: Paul Mackerras <paulus@ozlabs.org>
Subject: Re: [PATCH v10 7/8] KVM: PPC: Implement H_SVM_INIT_ABORT hcall
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Reply-To: Ram Pai <linuxram@us.ibm.com>
Cc: Sukadev Bhattiprolu <sukadev@linux.ibm.com>, cclaudio@linux.ibm.com,
 kvm-ppc@vger.kernel.org, Bharata B Rao <bharata@linux.ibm.com>,
 linux-mm@kvack.org, jglisse@redhat.com, Ram Pai <linuxram@linux.ibm.com>,
 aneesh.kumar@linux.vnet.ibm.com, paulus@au1.ibm.com,
 sukadev@linux.vnet.ibm.com, linuxppc-dev@lists.ozlabs.org, hch@lst.de
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On Wed, Nov 13, 2019 at 11:14:27AM +1100, Paul Mackerras wrote:
> On Tue, Nov 12, 2019 at 06:45:55AM -0800, Ram Pai wrote:
> > On Tue, Nov 12, 2019 at 10:32:04PM +1100, Paul Mackerras wrote:
> > > On Mon, Nov 11, 2019 at 11:52:15PM -0800, Ram Pai wrote:
> > > > There is subtle problem removing that code from the assembly.
> > > > 
> > > > If the H_SVM_INIT_ABORT hcall returns to the ultravisor without clearing
> > > > kvm->arch.secure_guest, the hypervisor will continue to think that the
> > > > VM is a secure VM.   However the primary reason the H_SVM_INIT_ABORT
> > > > hcall was invoked, was to inform the Hypervisor that it should no longer
> > > > consider the VM as a Secure VM. So there is a inconsistency there.
> > > 
> > > Most of the checks that look at whether a VM is a secure VM use code
> > > like "if (kvm->arch.secure_guest & KVMPPC_SECURE_INIT_DONE)".  Now
> > > since KVMPPC_SECURE_INIT_ABORT is 4, an if statement such as that will
> > > take the false branch once we have set kvm->arch.secure_guest to
> > > KVMPPC_SECURE_INIT_ABORT in kvmppc_h_svm_init_abort.  So in fact in
> > > most places we will treat the VM as a normal VM from then on.  If
> > > there are any places where we still need to treat the VM as a secure
> > > VM while we are processing the abort we can easily do that too.
> > 
> > Is the suggestion --  KVMPPC_SECURE_INIT_ABORT should never return back
> > to the Ultravisor?   Because removing that assembly code will NOT lead the
> 
> No.  The suggestion is that vcpu->arch.secure_guest stays set to
> KVMPPC_SECURE_INIT_ABORT until userspace calls KVM_PPC_SVM_OFF.

In the fast_guest_return path, if it finds 
(kvm->arch.secure_guest & KVMPPC_SECURE_INIT_ABORT) is true, should it return to
UV or not?

Ideally it should return back to the ultravisor the first time
KVMPPC_SECURE_INIT_ABORT is set, and not than onwards.

RP