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    Subject[tip:x86/asm] x86: Lift restriction on the location of FIX_BTMAP_*
    Commit-ID:  499a5f1efa0b0ac56ec5d060412aed84ae68e63e
    Gitweb: http://git.kernel.org/tip/499a5f1efa0b0ac56ec5d060412aed84ae68e63e
    Author: Jan Beulich <JBeulich@novell.com>
    AuthorDate: Fri, 18 Dec 2009 16:05:51 +0000
    Committer: Ingo Molnar <mingo@elte.hu>
    CommitDate: Wed, 30 Dec 2009 11:57:30 +0100

    x86: Lift restriction on the location of FIX_BTMAP_*

    The early ioremap fixmap entries cover half (or for 32-bit
    non-PAE, a quarter) of a page table, yet they got
    uncondtitionally aligned so far to a 256-entry boundary. This is
    not necessary if the range of page table entries anyway falls
    into a single page table.

    This buys back, for (theoretically) 50% of all configurations
    (25% of all non-PAE ones), at least some of the lowmem
    necessarily lost with commit e621bd18958ef5dbace3129ebe17a0a475e127d9.

    Signed-off-by: Jan Beulich <jbeulich@novell.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    LKML-Reference: <4B2BB66F0200007800026AD6@vpn.id2.novell.com>
    Signed-off-by: Ingo Molnar <mingo@elte.hu>
    ---
    arch/x86/include/asm/fixmap.h | 16 +++++++++++-----
    arch/x86/mm/ioremap.c | 4 ++++
    2 files changed, 15 insertions(+), 5 deletions(-)

    diff --git a/arch/x86/include/asm/fixmap.h b/arch/x86/include/asm/fixmap.h
    index 14f9890..635f03b 100644
    --- a/arch/x86/include/asm/fixmap.h
    +++ b/arch/x86/include/asm/fixmap.h
    @@ -118,14 +118,20 @@ enum fixed_addresses {
    * 256 temporary boot-time mappings, used by early_ioremap(),
    * before ioremap() is functional.
    *
    - * We round it up to the next 256 pages boundary so that we
    - * can have a single pgd entry and a single pte table:
    + * If necessary we round it up to the next 256 pages boundary so
    + * that we can have a single pgd entry and a single pte table:
    */
    #define NR_FIX_BTMAPS 64
    #define FIX_BTMAPS_SLOTS 4
    - FIX_BTMAP_END = __end_of_permanent_fixed_addresses + 256 -
    - (__end_of_permanent_fixed_addresses & 255),
    - FIX_BTMAP_BEGIN = FIX_BTMAP_END + NR_FIX_BTMAPS*FIX_BTMAPS_SLOTS - 1,
    +#define TOTAL_FIX_BTMAPS (NR_FIX_BTMAPS * FIX_BTMAPS_SLOTS)
    + FIX_BTMAP_END =
    + (__end_of_permanent_fixed_addresses ^
    + (__end_of_permanent_fixed_addresses + TOTAL_FIX_BTMAPS - 1)) &
    + -PTRS_PER_PTE
    + ? __end_of_permanent_fixed_addresses + TOTAL_FIX_BTMAPS -
    + (__end_of_permanent_fixed_addresses & (TOTAL_FIX_BTMAPS - 1))
    + : __end_of_permanent_fixed_addresses,
    + FIX_BTMAP_BEGIN = FIX_BTMAP_END + TOTAL_FIX_BTMAPS - 1,
    #ifdef CONFIG_PROVIDE_OHCI1394_DMA_INIT
    FIX_OHCI1394_BASE,
    #endif
    diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
    index c246d25..03c75ff 100644
    --- a/arch/x86/mm/ioremap.c
    +++ b/arch/x86/mm/ioremap.c
    @@ -422,6 +422,10 @@ void __init early_ioremap_init(void)
    * The boot-ioremap range spans multiple pmds, for which
    * we are not prepared:
    */
    +#define __FIXADDR_TOP (-PAGE_SIZE)
    + BUILD_BUG_ON((__fix_to_virt(FIX_BTMAP_BEGIN) >> PMD_SHIFT)
    + != (__fix_to_virt(FIX_BTMAP_END) >> PMD_SHIFT));
    +#undef __FIXADDR_TOP
    if (pmd != early_ioremap_pmd(fix_to_virt(FIX_BTMAP_END))) {
    WARN_ON(1);
    printk(KERN_WARNING "pmd %p != %p\n",

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