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    Subject[tip:x86/mm] x86/mm: Initialize 'pgdir_shift' and 'ptrs_per_p4d' at boot-time
    Commit-ID:  b16e770bfa5344f1cd4f7b4ecd7bbae25001e120
    Gitweb: https://git.kernel.org/tip/b16e770bfa5344f1cd4f7b4ecd7bbae25001e120
    Author: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    AuthorDate: Wed, 14 Feb 2018 21:25:35 +0300
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Fri, 16 Feb 2018 10:48:47 +0100

    x86/mm: Initialize 'pgdir_shift' and 'ptrs_per_p4d' at boot-time

    Switching between paging modes requires the folding of the p4d page table level
    when we only have 4 paging levels, which means we need to adjust 'pgdir_shift'
    and 'ptrs_per_p4d' during early boot according to paging mode.

    Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Arjan van de Ven <arjan@linux.intel.com>
    Cc: Borislav Petkov <bp@suse.de>
    Cc: Dan Williams <dan.j.williams@intel.com>
    Cc: Dave Hansen <dave.hansen@linux.intel.com>
    Cc: David Woodhouse <dwmw2@infradead.org>
    Cc: Josh Poimboeuf <jpoimboe@redhat.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: linux-mm@kvack.org
    Link: http://lkml.kernel.org/r/20180214182542.69302-3-kirill.shutemov@linux.intel.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    arch/x86/boot/compressed/kaslr.c | 6 ++++--
    arch/x86/kernel/head64.c | 6 ++++--
    2 files changed, 8 insertions(+), 4 deletions(-)

    diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
    index d02a838..66e42a0 100644
    --- a/arch/x86/boot/compressed/kaslr.c
    +++ b/arch/x86/boot/compressed/kaslr.c
    @@ -48,8 +48,8 @@

    #ifdef CONFIG_X86_5LEVEL
    unsigned int pgtable_l5_enabled __ro_after_init;
    -unsigned int pgdir_shift __ro_after_init = 48;
    -unsigned int ptrs_per_p4d __ro_after_init = 512;
    +unsigned int pgdir_shift __ro_after_init = 39;
    +unsigned int ptrs_per_p4d __ro_after_init = 1;
    #endif

    extern unsigned long get_cmd_line_ptr(void);
    @@ -732,6 +732,8 @@ void choose_random_location(unsigned long input,
    #ifdef CONFIG_X86_5LEVEL
    if (__read_cr4() & X86_CR4_LA57) {
    pgtable_l5_enabled = 1;
    + pgdir_shift = 48;
    + ptrs_per_p4d = 512;
    }
    #endif

    diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
    index ffb31c5..8a0a485 100644
    --- a/arch/x86/kernel/head64.c
    +++ b/arch/x86/kernel/head64.c
    @@ -42,9 +42,9 @@ pmdval_t early_pmd_flags = __PAGE_KERNEL_LARGE & ~(_PAGE_GLOBAL | _PAGE_NX);
    #ifdef CONFIG_X86_5LEVEL
    unsigned int pgtable_l5_enabled __ro_after_init;
    EXPORT_SYMBOL(pgtable_l5_enabled);
    -unsigned int pgdir_shift __ro_after_init = 48;
    +unsigned int pgdir_shift __ro_after_init = 39;
    EXPORT_SYMBOL(pgdir_shift);
    -unsigned int ptrs_per_p4d __ro_after_init = 512;
    +unsigned int ptrs_per_p4d __ro_after_init = 1;
    EXPORT_SYMBOL(ptrs_per_p4d);
    #endif

    @@ -79,6 +79,8 @@ static void __head check_la57_support(unsigned long physaddr)
    return;

    *fixup_int(&pgtable_l5_enabled, physaddr) = 1;
    + *fixup_int(&pgdir_shift, physaddr) = 48;
    + *fixup_int(&ptrs_per_p4d, physaddr) = 512;
    }
    #else
    static void __head check_la57_support(unsigned long physaddr) {}
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