Re: [PATCH 2/3 V7] KVM, SEV: Add support for SEV-ES intra host migration

From: Sean Christopherson <seanjc@google.com>
To: Peter Gonda <pgonda@google.com>
Cc: kvm@vger.kernel.org, Marc Orr <marcorr@google.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	David Rientjes <rientjes@google.com>,
	"Dr . David Alan Gilbert" <dgilbert@redhat.com>,
	Brijesh Singh <brijesh.singh@amd.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/3 V7] KVM, SEV: Add support for SEV-ES intra host migration
Date: Fri, 10 Sep 2021 01:20:07 +0000	[thread overview]
Message-ID: <YTqyx0J0Ik7wqx/+@google.com> (raw)
In-Reply-To: <YTqr4nuXYVFz81kD@google.com>

On Fri, Sep 10, 2021, Sean Christopherson wrote:
> On Thu, Sep 02, 2021, Peter Gonda wrote:
> > diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> > index 8db666a362d4..fac21a82e4de 100644
> > --- a/arch/x86/kvm/svm/sev.c
> > +++ b/arch/x86/kvm/svm/sev.c
> > @@ -1545,6 +1545,59 @@ static void migrate_info_from(struct kvm_sev_info *dst,
> >  	list_replace_init(&src->regions_list, &dst->regions_list);
> >  }
> >  
> > +static int migrate_vmsa_from(struct kvm *dst, struct kvm *src)

Better to call this sev_es_migrate_from()...

> > +{
> > +	int i, num_vcpus;
> > +	struct kvm_vcpu *dst_vcpu, *src_vcpu;
> > +	struct vcpu_svm *dst_svm, *src_svm;
> > +

...because this should also clear kvm->es_active.  KVM_SEV_INIT isn't problematic
(as currently written) because the common sev_guest_init() explicitly writes es_active,
but I think a clever userspace could get an SEV ASID into an "ES" guest via
KVM_CAP_VM_COPY_ENC_CONTEXT_FROM, which requires its dst to be !SEV and thus
doesn't touch es_active.

Huh, that's a bug, svm_vm_copy_asid_from() should explicitly disallow copying the
ASID from an SEV-ES guest.  I'll send a patch for that.

Last thought, it's probably worth renaming migrate_info_from() to sev_migrate_from()
to pair with sev_es_migrate_from().