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SubjectRe: [PATCH] x86/mm: Expand static page table for fixmap space
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On 17/09/18 09:34, Feng Tang wrote:
> We met a kernel panic when enabling earlycon, which is due to
> the fixmap address of earlycon is not statically setup.
>
> Currently the static fixmap setup in head_64.S only covers 2M
> virtual address space, while it acutually could be in 4M space
> with different kernel configurations.
>
> So increase the static space to 4M for now by defining FIXMAP_PMD_NUM
> to 2, and add a build time check for future possible overflow so that
> the macro could be increased accordingly.
>
> Suggested-by: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Feng Tang <feng.tang@intel.com>
> ---
> arch/x86/include/asm/fixmap.h | 3 +++
> arch/x86/include/asm/pgtable_64.h | 3 ++-
> arch/x86/kernel/head_64.S | 16 ++++++++++++----
> arch/x86/mm/pgtable.c | 10 ++++++++++
> arch/x86/xen/mmu_pv.c | 4 +++-
> 5 files changed, 30 insertions(+), 6 deletions(-)
>

...

> diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c
> index 2fe5c9b..19077f9 100644
> --- a/arch/x86/xen/mmu_pv.c
> +++ b/arch/x86/xen/mmu_pv.c
> @@ -1952,7 +1952,9 @@ void __init xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn)
> set_page_prot(level2_ident_pgt, PAGE_KERNEL_RO);
> set_page_prot(level2_kernel_pgt, PAGE_KERNEL_RO);
> set_page_prot(level2_fixmap_pgt, PAGE_KERNEL_RO);
> - set_page_prot(level1_fixmap_pgt, PAGE_KERNEL_RO);
> +
> + for (i = 0; i < FIXMAP_PMD_NUM; i++)
> + set_page_prot(level1_fixmap_pgt + i * 512, PAGE_KERNEL_RO);

Please use PTRS_PER_PTE instead of the literal 512.

Some lines further up level1_fixmap_pgt is mentioned in a comment.
Please update that, too:

- /* L3_k[511][506] -> level1_fixmap_pgt */
+ /* L3_k[511][506, ...] -> level1_fixmap_pgt */


Juergen

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