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    SubjectRe: 2.6.25-rc1 xen pvops regression
    Jody Belka wrote:
    > Hi all,
    > I thought I'd try out 2.6.25-rc1 as a xen 32-bit pae domU the other day.
    > Unfortunately, I didn't get very far very fast, as the domain just crashed
    > immediately upon booting, without any direct feedback (I did have messages
    > on the xen message buffer, which helped). This even with earlyprintk turned on.
    > After a long, arduous journey, I managed to track this down to the following:
    > ----------
    > commit 551889a6e2a24a9c06fd453ea03b57b7746ffdc0
    > x86: construct 32-bit boot time page tables in native format.
    > Specifically the boot time page tables in a CONFIG_X86_PAE=y enabled
    > kernel are in PAE format.
    > early_ioremap is updated to use the standard page table accessors.
    > Clear any mappings beyond max_low_pfn from the boot page tables in
    > native_pagetable_setup_start because the initial mappings can extend
    > beyond the range of physical memory and into the vmalloc area.
    > Derived from patches by Eric Biederman and H. Peter Anvin.
    > [ PAE swapper_pg_dir needs to be page-sized fix ]
    > ----------
    > However, to make life more interesting, just reverting this isn't quite
    > enough to get us to the promised land. If we try, we find that although
    > we do now start booting, we crash again a short way into the process.
    > In a different manner though. Specifically, in early_ioremap_clear.
    > Reverting the above commit /except/ for the changes to arch/x86/mm/ioremap.c
    > gets everything working again.
    > Well, except that we can't shutdown/reboot properly, but I've sent a patch
    > for that in another email.
    > I'm afraid i've no idea what needs to be done to get the change to work
    > with xen, but i'm willing to try out any patches people come up with.
    > Please cc me on any replies, as i'm not subscribed, thanks.


    Although I'm on vacation, I happened to download a recent copy of
    x86.git and found that it crashes early. Here's a couple of patches to
    apply; I don't know if they apply to current git, but I hope it helps.

    Subject: x86/early_ioremap: don't assume we're using swapper_pg_dir

    At the early stages of boot, before the kernel pagetable has been
    fully initialized, a Xen kernel will still be running off the
    Xen-provided pagetables rather than swapper_pg_dir[]. Therefore,
    readback cr3 to determine the base of the pagetable rather than
    assuming swapper_pg_dir[].

    Signed-off-by: Jeremy Fitzhardinge <>

    arch/x86/mm/ioremap.c | 4 +++-
    1 file changed, 3 insertions(+), 1 deletion(-)

    --- a/arch/x86/mm/ioremap.c
    +++ b/arch/x86/mm/ioremap.c
    @@ -265,7 +265,9 @@

    static inline pmd_t * __init early_ioremap_pmd(unsigned long addr)
    - pgd_t *pgd = &swapper_pg_dir[pgd_index(addr)];
    + /* Don't assume we're using swapper_pg_dir at this point */
    + pgd_t *base = __va(read_cr3());
    + pgd_t *pgd = &base[pgd_index(addr)];
    pud_t *pud = pud_offset(pgd, addr);
    pmd_t *pmd = pmd_offset(pud, addr);
    Subject: xen: unpin initial Xen pagetable once we're finished with it

    Unpin the Xen-provided pagetable once we've finished with it, so it
    doesn't cause stray references which cause later swapper_pg_dir
    pagetable updates to fail.

    Signed-off-by: Jeremy Fitzhardinge <>

    arch/x86/xen/enlighten.c | 4 ++++
    1 file changed, 4 insertions(+)

    --- a/arch/x86/xen/enlighten.c
    +++ b/arch/x86/xen/enlighten.c
    @@ -798,6 +798,10 @@
    * added to the table can be prepared properly for Xen.
    + /* Unpin initial Xen pagetable */
    + pin_pagetable_pfn(MMUEXT_UNPIN_TABLE,
    + PFN_DOWN(__pa(xen_start_info->pt_base)));

    static __init void xen_pagetable_setup_done(pgd_t *base)
     \ /
      Last update: 2008-02-13 13:03    [W:0.025 / U:14.012 seconds]
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