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    Subject[tip:x86/mm2] x86, 64bit: #PF handler set page to cover only 2M per #PF
    Commit-ID:  6b9c75aca6cba4d99a6e8d8274b1788d4d4b50d9
    Gitweb: http://git.kernel.org/tip/6b9c75aca6cba4d99a6e8d8274b1788d4d4b50d9
    Author: Yinghai Lu <yinghai@kernel.org>
    AuthorDate: Thu, 24 Jan 2013 12:19:53 -0800
    Committer: H. Peter Anvin <hpa@linux.intel.com>
    CommitDate: Tue, 29 Jan 2013 15:20:13 -0800

    x86, 64bit: #PF handler set page to cover only 2M per #PF

    We only map a single 2 MiB page per #PF, even though we should be able
    to do this a full gigabyte at a time with no additional memory cost.
    This is a workaround for a broken AMD reference BIOS (and its
    derivatives in shipping system) which maps a large chunk of memory as
    WB in the MTRR system but will #MC if the processor wanders off and
    tries to prefetch that memory, which can happen any time the memory is
    mapped in the TLB.

    Signed-off-by: Yinghai Lu <yinghai@kernel.org>
    Link: http://lkml.kernel.org/r/1359058816-7615-13-git-send-email-yinghai@kernel.org
    Cc: Alexander Duyck <alexander.h.duyck@intel.com>
    [ hpa: rewrote the patch description ]
    Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
    ---
    arch/x86/kernel/head64.c | 42 +++++++++++++++++++++++++-----------------
    1 file changed, 25 insertions(+), 17 deletions(-)

    diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
    index f57df05..816fc85 100644
    --- a/arch/x86/kernel/head64.c
    +++ b/arch/x86/kernel/head64.c
    @@ -53,15 +53,15 @@ int __init early_make_pgtable(unsigned long address)
    unsigned long physaddr = address - __PAGE_OFFSET;
    unsigned long i;
    pgdval_t pgd, *pgd_p;
    - pudval_t *pud_p;
    + pudval_t pud, *pud_p;
    pmdval_t pmd, *pmd_p;

    /* Invalid address or early pgt is done ? */
    if (physaddr >= MAXMEM || read_cr3() != __pa(early_level4_pgt))
    return -1;

    - i = (address >> PGDIR_SHIFT) & (PTRS_PER_PGD - 1);
    - pgd_p = &early_level4_pgt[i].pgd;
    +again:
    + pgd_p = &early_level4_pgt[pgd_index(address)].pgd;
    pgd = *pgd_p;

    /*
    @@ -69,29 +69,37 @@ int __init early_make_pgtable(unsigned long address)
    * critical -- __PAGE_OFFSET would point us back into the dynamic
    * range and we might end up looping forever...
    */
    - if (pgd && next_early_pgt < EARLY_DYNAMIC_PAGE_TABLES) {
    + if (pgd)
    pud_p = (pudval_t *)((pgd & PTE_PFN_MASK) + __START_KERNEL_map - phys_base);
    - } else {
    - if (next_early_pgt >= EARLY_DYNAMIC_PAGE_TABLES-1)
    + else {
    + if (next_early_pgt >= EARLY_DYNAMIC_PAGE_TABLES) {
    reset_early_page_tables();
    + goto again;
    + }

    pud_p = (pudval_t *)early_dynamic_pgts[next_early_pgt++];
    for (i = 0; i < PTRS_PER_PUD; i++)
    pud_p[i] = 0;
    -
    *pgd_p = (pgdval_t)pud_p - __START_KERNEL_map + phys_base + _KERNPG_TABLE;
    }
    - i = (address >> PUD_SHIFT) & (PTRS_PER_PUD - 1);
    - pud_p += i;
    -
    - pmd_p = (pmdval_t *)early_dynamic_pgts[next_early_pgt++];
    - pmd = (physaddr & PUD_MASK) + (__PAGE_KERNEL_LARGE & ~_PAGE_GLOBAL);
    - for (i = 0; i < PTRS_PER_PMD; i++) {
    - pmd_p[i] = pmd;
    - pmd += PMD_SIZE;
    - }
    + pud_p += pud_index(address);
    + pud = *pud_p;

    - *pud_p = (pudval_t)pmd_p - __START_KERNEL_map + phys_base + _KERNPG_TABLE;
    + if (pud)
    + pmd_p = (pmdval_t *)((pud & PTE_PFN_MASK) + __START_KERNEL_map - phys_base);
    + else {
    + if (next_early_pgt >= EARLY_DYNAMIC_PAGE_TABLES) {
    + reset_early_page_tables();
    + goto again;
    + }
    +
    + pmd_p = (pmdval_t *)early_dynamic_pgts[next_early_pgt++];
    + for (i = 0; i < PTRS_PER_PMD; i++)
    + pmd_p[i] = 0;
    + *pud_p = (pudval_t)pmd_p - __START_KERNEL_map + phys_base + _KERNPG_TABLE;
    + }
    + pmd = (physaddr & PMD_MASK) + (__PAGE_KERNEL_LARGE & ~_PAGE_GLOBAL);
    + pmd_p[pmd_index(address)] = pmd;

    return 0;
    }

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