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    SubjectRe: [PATCH v2 04/13] arm64: decouple early fixmap init from linear mapping
    Hi Ard!

    On 30/12/15 15:26, Ard Biesheuvel wrote:
    > Since the early fixmap page tables are populated using pages that are
    > part of the static footprint of the kernel, they are covered by the
    > initial kernel mapping, and we can refer to them without using __va/__pa
    > translations, which are tied to the linear mapping.
    >
    > Instead, let's introduce __phys_to_kimg, which will be tied to the kernel
    > virtual mapping, regardless of whether or not it intersects with the linear
    > mapping. This will allow us to move the kernel out of the linear mapping in
    > a subsequent patch.
    >

    I gave your arm64-kaslr-v2 branch a go on juno r1, currently with
    ARM64_RELOCATABLE_KERNEL=n, to find it didn't boot.

    git bisect pointed to this patch. From the debugger it looks like
    rubbish is ending up the page tables after early_fixmap_init(), printing
    bits of bm_pmd and friends shows these aren't zeroed.

    I think this is because the section(".pgdir") is dragging these outside
    the __bss_start/__bss_stop range that is zeroed in head.S:__mmap_switched().

    The following inelegant patch fixes this problem for me:
    ----------------------------%<----------------------------
    diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
    index a78fc5a882da..15fc9712ddc1 100644
    --- a/arch/arm64/mm/mmu.c
    +++ b/arch/arm64/mm/mmu.c
    @@ -559,6 +559,7 @@ void __init early_fixmap_init(void)
    if (pgd_none(*pgd)) {
    static pud_t bm_pud[PTRS_PER_PUD] __pgdir;

    + memset(bm_pud, 0, sizeof(bm_pud));
    pgd_populate(&init_mm, pgd, bm_pud);
    memblock_reserve(__pa(bm_pud), sizeof(bm_pud));
    }
    @@ -570,6 +571,7 @@ void __init early_fixmap_init(void)
    if (pud_none(*pud)) {
    static pmd_t bm_pmd[PTRS_PER_PMD] __pgdir;

    + memset(bm_pmd, 0, sizeof(bm_pmd));
    pud_populate(&init_mm, pud, bm_pmd);
    memblock_reserve(__pa(bm_pmd), sizeof(bm_pmd));
    }
    @@ -580,6 +582,7 @@ void __init early_fixmap_init(void)
    if (pmd_none(*pmd)) {
    static pte_t bm_pte[PTRS_PER_PTE] __pgdir;

    + memset(bm_pte, 0, sizeof(bm_pte));
    pmd_populate_kernel(&init_mm, pmd, bm_pte);
    memblock_reserve(__pa(bm_pte), sizeof(bm_pte));
    }
    ----------------------------%<----------------------------
    I'm sure there is a better way!


    Thanks,

    James



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