Re: [Qemu-devel] [QEMU PATCH v4 0/10]: target/i386: kvm: Add support for save and restore of nested state

[Paolo Bonzini <pbonzini@redhat.com>]

On 19/06/19 18:21, Liran Alon wrote:
> Hi,
> 
> This series aims to add support for QEMU to be able to migrate VMs that
> are running nested hypervisors. In order to do so, it utilizes the new
> IOCTLs introduced in KVM commit 8fcc4b5923af ("kvm: nVMX: Introduce
> KVM_CAP_NESTED_STATE") which was created for this purpose.

Applied with just three minor changes that should be uncontroversial:

> 6rd patch updates linux-headers to have updated struct kvm_nested_state.
> The updated struct now have explicit fields for the data portion.

Changed patch title to "linux-headers: sync with latest KVM headers from
Linux 5.2"

> 7rd patch add vmstate support for saving/restoring kernel integer types (e.g. __u16).
> 
> 8th patch adds support for saving and restoring nested state in order to migrate
> guests which run a nested hypervisor.

diff --git a/target/i386/kvm.c b/target/i386/kvm.c
index e924663f32..f3cf6e1b27 100644
--- a/target/i386/kvm.c
+++ b/target/i386/kvm.c
@@ -1671,10 +1671,10 @@ int kvm_arch_init_vcpu(CPUState *cs)
             struct kvm_vmx_nested_state_hdr *vmx_hdr =
                 &env->nested_state->hdr.vmx;

+            env->nested_state->format = KVM_STATE_NESTED_FORMAT_VMX;
             vmx_hdr->vmxon_pa = -1ull;
             vmx_hdr->vmcs12_pa = -1ull;
         }
-
     }

     cpu->kvm_msr_buf = g_malloc0(MSR_BUF_SIZE);

which is a no-op since KVM_STATE_NESTED_FORMAT_VMX is zero, but it's tidy.

> 9th patch add support for KVM_CAP_EXCEPTION_PAYLOAD. This new KVM capability
> allows userspace to properly distingiush between pending and injecting exceptions.
> 
> 10th patch changes the nested virtualization migration blocker to only
> be added when kernel lack support for one of the capabilities required
> for correct nested migration. i.e. Either KVM_CAP_NESTED_STATE or
> KVM_CAP_EXCEPTION_PAYLOAD.

Had to disable this for SVM unfortunately.