Re: [Qemu-devel] [PATCH v4 0/6] save/restore on Xen

[Stefano Stabellini]

On Mon, 23 Jan 2012, Jan Kiszka wrote:
> >> Or what is the ordering
> >> of init, RAM restore, and initial device reset now?
> > 
> > RAM restore (done by Xen)
> > 
> > physmap rebuild (done by xen_hvm_init in qemu)
> > pc_init()
> > qemu_system_reset()
> > load_vmstate()
> 
> Hmm, are you sure that this is the only case where a device init or
> reset handler writes to already restored guest memory? Preloading the
> RAM this way is a non-standard scenario for QEMU, thus conceptually
> fragile. Does restoring happen before QEMU is even started, or can this
> point be controlled from QEMU?

Consider that this only happens with non-MMIO device memory, in practice
only videoram.
Vmware VGA does not memset the videoram in the reset handler, while QXL
already has the following:

    /* pre loadvm reset must not touch QXLRam.  This lives in
     * device memory, is migrated together with RAM and thus
     * already loaded at this point */
    if (!loadvm) {
        qxl_reset_state(d);
    }