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

[Juergen Gross <jgross@xxxxxxxx>]

On 10/29/2014 06:30 AM, Juergen Gross wrote:
> 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...
Wait, now I see my fault: by doing the remapping later I've skipped the
highmem check during adding the memory to the system. Okay, I'll update
the patch.


Juergen


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