[PATCH][4.17?] VMX: correct error handling in vmx_create_vmcs()

[Jan Beulich]

With the addition of vmx_add_msr() calls to construct_vmcs() there are
now cases where simply freeing the VMCS isn't enough: The MSR bitmap
page as well as one of the MSR area ones (if it's the 2nd vmx_add_msr()
which fails) may also need freeing. Switch to using vmx_destroy_vmcs()
instead.

Fixes: 3bd36952dab6 ("x86/spec-ctrl: Introduce an option to control L1D_FLUSH 
for HVM HAP guests")
Fixes: 53a570b28569 ("x86/spec-ctrl: Support IBPB-on-entry")
Reported-by: Andrew Cooper <andrew.coop...@citrix.com>
Signed-off-by: Jan Beulich <jbeul...@suse.com>
---
With both referenced commits having been for XSAs, we may want to
consider backporting this also to security-only stable trees. Otoh it's
"just" an error path ...

--- a/xen/arch/x86/hvm/vmx/vmcs.c
+++ b/xen/arch/x86/hvm/vmx/vmcs.c
@@ -1821,7 +1821,7 @@ int vmx_create_vmcs(struct vcpu *v)
 
     if ( (rc = construct_vmcs(v)) != 0 )
     {
-        vmx_free_vmcs(vmx->vmcs_pa);
+        vmx_destroy_vmcs(v);
         return rc;
     }