Re: [Xen-devel] [PATCH 1/2] Xen: Delay remapping memory of pv-domain

[Juergen Gross <jgross@xxxxxxxx>]

On 10/28/2014 06:34 PM, David Vrabel wrote:
> Can these patches be split up?  They're hard to review as-is.  e.g., the
> changes to page allocation look they could be split out.
>
> On 27/10/14 14:52, Juergen Gross wrote:
> > Early in the boot process the memory layout of a pv-domain is changed
> > to match the E820 map (either the host one for Dom0 or the Xen one)
> > regarding placement of RAM and PCI holes. This requires removing memory
> > pages initially located at positions not suitable for RAM and adding
> > them later at higher addresses where no restrictions apply.
> How does this impact Matt Rushton's recent change to ensure the
> relocated frames are contiguous?
It is simplifying it. :-)

The relocated frames are in the same sequence as before, just at
another location. As the remapping is done later, I don't have to be
careful not to cross a p2m leaf page boundary (allocating a new leaf
page is no problem now).

> The change was "xen/setup: Remap Xen Identity Mapped RAM" (4fbb67e3c87).
>
> > +       /* Update kernel mapping */
> > +       if (HYPERVISOR_update_va_mapping((unsigned long)__va(pfn << PAGE_SHIFT),
> > +                                        mfn_pte(mfn, PAGE_KERNEL), 0)) {
> > +               WARN(1, "Failed to update kernel mapping for mfn=%ld pfn=%ld\n",
> > +                     mfn, pfn);
> > +               return 0;
> I think you need to check if this is a PFN for a high page before
> updating the mapping.
Really? I'm not aware of having removed such a check. If it is really
necessary it must have been missing before...


Juergen

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