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[Xen-devel] Re: Making pages writable again in paging_log_dirty mode

  • To: xen-devel@xxxxxxxxxxxxxxxxxxx
  • From: "Mike Sun" <msun@xxxxxxxxxx>
  • Date: Fri, 19 Dec 2008 16:08:01 -0500
  • Delivery-date: Fri, 19 Dec 2008 13:08:30 -0800
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  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>

> Unfortunately, I get errors about page_type_count
> overflows and other kinds of type errors.

I forgot to mention that I'm ending up here:

int get_page_type(struct page_info *page, unsigned long type)
        nx = x + 1;
        if ( unlikely((nx & PGT_count_mask) == 0) )
            MEM_LOG("Type count overflow on pfn %lx", page_to_mfn(page));
            return 0;

Not sure how I'm ending up with a -1 type count.  I noticed this code
in "get_page_from_l1e()":

/* Foreign mappings into guests in shadow external mode don't
     * contribute to writeable mapping refcounts.  (This allows the
     * qemu-dm helper process in dom0 to map the domain's memory without
     * messing up the count of "real" writable mappings.) */
    okay = (((l1f & _PAGE_RW) &&
             !(unlikely(paging_mode_external(d) && (d != curr->domain))))
            ? get_page_and_type(page, d, PGT_writable_page)
            : get_page(page, d));

I believe since I'm trying to make writable pages of an HVM guest
domain from dom0 in log_dirty_mode, I'm going to end up just doing the
get_page() instead of the get_page_and_type().  Is this my problem?


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