i386/sev: Set CPU state to protected once SNP guest payload is finalized

i386/sev: Set CPU state to protected once SNP guest payload is finalized

Once KVM_SNP_LAUNCH_FINISH is called the vCPU state is copied into the
vCPU's VMSA page and measured/encrypted. Any attempt to read/write CPU
state afterward will only be acting on the initial data and so are
effectively no-ops.

Set the vCPU state to protected at this point so that QEMU don't
continue trying to re-sync vCPU data during guest runtime.

Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Pankaj Gupta <pankaj.gupta@amd.com>
Message-ID: <20240530111643.1091816-18-pankaj.gupta@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>