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    SubjectRe: [PATCH 6/7] x86, mm: setup page table from top-down
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    On Wed, Oct 10, 2012 at 9:38 AM, Stefano Stabellini
    <stefano.stabellini@eu.citrix.com> wrote:
    >> - if (pfn >= pgt_buf_top)
    >> - panic("alloc_low_page: ran out of memory");
    >> + if ((pgt_buf_end + 1) >= pgt_buf_top) {
    >> + unsigned long ret;
    >> + if (min_pfn_mapped >= max_pfn_mapped)
    >> + panic("alloc_low_page: ran out of memory");
    >> + ret = memblock_find_in_range(min_pfn_mapped << PAGE_SHIFT,
    >> + max_pfn_mapped << PAGE_SHIFT,
    >> + PAGE_SIZE, PAGE_SIZE);
    >> + if (!ret)
    >> + panic("alloc_low_page: can not alloc memory");
    >> + memblock_reserve(ret, PAGE_SIZE);
    >> + pfn = ret >> PAGE_SHIFT;
    >
    > This cannot be right: you are allocating another page to be used as
    > pagetable page, outside the range pgt_buf_start-pgt_buf_top.
    >
    > When that page is going to be hooked into the live pagetable, the kernel
    > is going to panic on Xen because the page wasn't marked RO.
    >
    > If you want to do that you need to tell the Xen subsystem of the new
    > page. pagetable_reserve is not the right call, we need a new one (see
    > past emails).

    ok, will change that interface and call in from alloc_low_page.

    how about the pages from BRK, do we need to call xen hooks to mark it as RO?


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