KVM: nVMX: Allocate shadow vmcs

Allocate a shadow vmcs used by the processor to shadow part of the fields
stored in the software defined VMCS12 (let L1 access fields without causing
exits). Note we keep a shadow vmcs only for the current vmcs12.  Once a vmcs12
becomes non-current, its shadow vmcs is released.

Signed-off-by: Abel Gordon <abelg@il.ibm.com>
Reviewed-by: Orit Wasserman <owasserm@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 1cdfb5d7580a..7b27af9a14d8 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -355,6 +355,7 @@ struct nested_vmx {
         /* The host-usable pointer to the above */
         struct page *current_vmcs12_page;
         struct vmcs12 *current_vmcs12;
+        struct vmcs *current_shadow_vmcs;
 
         /* vmcs02_list cache of VMCSs recently used to run L2 guests */
         struct list_head vmcs02_pool;
@@ -5527,6 +5528,7 @@ static int handle_vmon(struct kvm_vcpu *vcpu)
 {
         struct kvm_segment cs;
         struct vcpu_vmx *vmx = to_vmx(vcpu);
+        struct vmcs *shadow_vmcs;
 
         /* The Intel VMX Instruction Reference lists a bunch of bits that
          * are prerequisite to running VMXON, most notably cr4.VMXE must be
@@ -5555,6 +5557,16 @@ static int handle_vmon(struct kvm_vcpu *vcpu)
                 skip_emulated_instruction(vcpu);
                 return 1;
         }
+        if (enable_shadow_vmcs) {
+                shadow_vmcs = alloc_vmcs();
+                if (!shadow_vmcs)
+                        return -ENOMEM;
+                /* mark vmcs as shadow */
+                shadow_vmcs->revision_id |= (1u << 31);
+                /* init shadow vmcs */
+                vmcs_clear(shadow_vmcs);
+                vmx->nested.current_shadow_vmcs = shadow_vmcs;
+        }
 
         INIT_LIST_HEAD(&(vmx->nested.vmcs02_pool));
         vmx->nested.vmcs02_num = 0;