Re: [PATCH v2] x86/HVM: correct page dirty marking in hvm_map_guest_frame_rw()

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 22/09/15 13:53, Jan Beulich wrote:
> Rather than dirtying a page when establishing a (permanent) mapping,
> dirty it when the page gets unmapped, or - if still mapped - on the
> final iteration of a save operation (or in other cases where the guest
> is paused or already shut down). (Transient mappings continue to get
> dirtied upon getting mapped, to avoid the overhead of tracking.)
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> ---
> v2: Refine predicate for calling hvm_mapped_guest_frames_mark_dirty()
>      (now including all shut down domains as well as tool stack paused
>      ones).

I am still convinced that it is wrong for Xen to second-guess what libxc 
is actually doing.

libxc should explicitly ask for the permanent mappings (or not) via 
another bit in a shadow op.  Anything else risks not getting the bits 
set (so memory corruption), or having too many bits set in 
non-interested cases (unwanted overhead).

~Andrew