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    Subject[PATCH 16/16] xen/i386: make sure initial VGA/ISA mappings are not overridden
    Date
    From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

    arch/x86/mm/init_32.c overrides the ISA/VGA mappings with direct mappings
    which do not have _PAGE_IOMAP set, thereby making the ISA space inaccessible.

    This patch adds to the existing hack to make sure the pre-constructed
    ISA mappings are not incorrectly overwritten.

    Thanks to Gerd Hoffman for pointing this out.

    [ Impact: Makes 32-bit dom0 VGA work properly. ]

    Diagnosed-by: Gerd Hoffmann <kraxel@redhat.com>
    Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
    ---
    arch/x86/xen/mmu.c | 11 +++++++++--
    1 files changed, 9 insertions(+), 2 deletions(-)

    diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
    index 85d9d18..331e52d 100644
    --- a/arch/x86/xen/mmu.c
    +++ b/arch/x86/xen/mmu.c
    @@ -1502,10 +1502,17 @@ static void *xen_kmap_atomic_pte(struct page *page, enum km_type type)
    #ifdef CONFIG_X86_32
    static __init pte_t mask_rw_pte(pte_t *ptep, pte_t pte)
    {
    - /* If there's an existing pte, then don't allow _PAGE_RW to be set */
    - if (pte_val_ma(*ptep) & _PAGE_PRESENT)
    + pte_t oldpte = *ptep;
    +
    + if (pte_flags(oldpte) & _PAGE_PRESENT) {
    + /* Don't allow existing IO mappings to be overridden */
    + if (pte_flags(oldpte) & _PAGE_IOMAP)
    + pte = oldpte;
    +
    + /* Don't allow _PAGE_RW to be set on existing pte */
    pte = __pte_ma(((pte_val_ma(*ptep) & _PAGE_RW) | ~_PAGE_RW) &
    pte_val_ma(pte));
    + }

    return pte;
    }
    --
    1.6.0.6


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