KVM: Validate hva in kvm_gpc_activate_hva() to fix __kvm_gpc_refresh() WARN

Check that the virtual address is "ok" when activating a gfn_to_pfn_cache
with a host VA to ensure that KVM never attempts to use a bad address.

This fixes a bug where KVM fails to check the incoming address when
handling KVM_XEN_VCPU_ATTR_TYPE_VCPU_INFO_HVA in kvm_xen_vcpu_set_attr().

Reported-by:  <syzbot+fd555292a1da3180fc82@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=fd555292a1da3180fc82


Tested-by:  <syzbot+fd555292a1da3180fc82@syzkaller.appspotmail.com>
Signed-off-by: Pei Li <peili.dev@gmail.com>
Reviewed-by: Paul Durrant <paul@xen.org>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Link: https://lore.kernel.org/r/20240627-bug5-v2-1-2c63f7ee6739@gmail.com


[sean: rewrite changelog with --verbose]
Signed-off-by: Sean Christopherson <seanjc@google.com>