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Re: [Xen-devel] [PATCH v1 2/8]: PVH mmu changes

On Mon, 24 Sep 2012 12:55:31 +0100
Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx> wrote:

> There are few code style issues on this patch, I suggest you run it
> through scripts/checkpatch.pl, it should be able to catch all these
> errors.

All patches were run thru checkpatch.pl already. So not sure what you
are referring to.

> > +   struct pvh_remap_data *remapp = data;
> > +   struct xen_pvh_pfn_info *pvhp = remapp->pvhinfop;
> > +   unsigned long pfn =
> > page_to_pfn(pvhp->pi_paga[pvhp->pi_next_todo++]);
> > +   pte_t pteval = pte_mkspecial(pfn_pte(pfn, remapp->prot));
> > +
> > +   if ((rc=pvh_add_to_xen_p2m(pfn, remapp->fgmfn,
> > remapp->domid)))
> > +           return rc;
> > +   native_set_pte(ptep, pteval);
> Do we actually need the pte to be "special"?
> I would think that being in the guest p2m, it is actually quite a
> normal page.

Hmm... well, doesn't like removing "special":

BUG: Bad page map in process xl  pte:800000027b57b467 pmd:2b408d067
page:ffffea0008afb2e8 count:1 mapcount:-1 mapping:          (null) index:0x0
page flags: 0x40000000000414(referenced|dirty|reserved)
addr:00007fb4345b0000 vm_flags:000a44fb anon_vma:          (null) 
mapping:ffff88003911a3d0 index:4
vma->vm_ops->fault: privcmd_fault+0x0/0x40
vma->vm_file->f_op->mmap: privcmd_mmap+0x0/0x30
Pid: 2737, comm: xl Tainted: G    B        3.6.0-rc6-merge+ #17
Call Trace:
 [<ffffffff8113dabc>] print_bad_pte+0x1dc/0x250
 [<ffffffff8113e57e>] zap_pte_range+0x45e/0x4c0
 [<ffffffff8113f30e>] unmap_page_range+0x1ae/0x310
 [<ffffffff8113f4d1>] unmap_single_vma+0x61/0xe0
 [<ffffffff8113f5a4>] unmap_vmas+0x54/0xa0
 [<ffffffff8114514b>] unmap_region+0xab/0x120
 [<ffffffff81313263>] ? privcmd_ioctl+0x93/0x100
 [<ffffffff8114733d>] do_munmap+0x25d/0x380

This from:
                        if (unlikely(page_mapcount(page) < 0))
                                print_bad_pte(vma, addr, ptent, page);

So, the mapcount must be not be getting set in "normal" case properly it
appears. Marking it special causes it so skip few things. Debugging...


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