i386: hvf: Don't duplicate register reset

i386: hvf: Don't duplicate register reset

hvf_reset_vcpu() duplicates actions performed by x86_cpu_reset(). The
difference is that hvf_reset_vcpu() stores initial values directly to
VMCS while x86_cpu_reset() stores it in CPUX86State and then
cpu_synchronize_all_post_init() or cpu_synchronize_all_post_reset()
flushes CPUX86State into VMCS. That makes hvf_reset_vcpu() a kind of
no-op.

Here's the trace of CPU state modifications during VM start:
  hvf_reset_vcpu (resets VMCS)
  cpu_synchronize_all_post_init (overwrites VMCS fields written by
                                 hvf_reset_vcpu())
  cpu_synchronize_all_states
  hvf_reset_vcpu (resets VMCS)
  cpu_synchronize_all_post_reset (overwrites VMCS fields written by
                                  hvf_reset_vcpu())

General purpose registers, system registers, segment descriptors, flags
and IP are set by hvf_put_segments() in post-init and post-reset,
therefore it's safe to remove them from hvf_reset_vcpu().

PDPTE initialization can be dropped because Intel SDM (26.3.1.6 Checks
on Guest Page-Directory-Pointer-Table Entries) doesn't require PDPTE to
be clear unless PAE is used: "A VM entry to a guest that does not use
PAE paging does not check the validity of any PDPTEs."
And if PAE is used, PDPTE's are initialized from CR3 in macvm_set_cr0().

Cc: Cameron Esfahani <dirty@apple.com>
Signed-off-by: Roman Bolshakov <r.bolshakov@yadro.com>
Message-Id: <20200630102824.77604-8-r.bolshakov@yadro.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>