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

["Mike Sun" <msun@xxxxxxxxxx>]

> IIRC, They should stay as PGT_writeable, with a type count of zero.

Thanks a bunch Tim.  In tracking down my overflow problem, it lead me
to find that that the "get_page_from_l1e()" function has this bit of
code that is causing my problem:

    /* 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));

Basically, I'm trying to make an HVM guest's pages writable again via
a hypercall from dom0, and so this piece of code messes up the type
count since I'm actually changing "proper" writeable mapping
refcounts.  For now, I'm just calling an extra
"get_page_and_type(page, d, PGT_writable_page)" manually, and I think
it solves this problem, but I'm getting a different kind of kernel
panic now where it complains about not being able to
"rm_write_access()" due to some special mappings.  Any ideas?

-- Mike

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