On 13 Aug 2020, at 20:51, Mike Rapoport <rppt@xxxxxxxxxx> wrote:
>
> From: Jessica Clarke <jrtc27@xxxxxxxxxx>
>
> IA-64 is special and treats pgd_offset_k() differently to pgd_offset(),
> using different formulae to calculate the indices into the kernel and user
> PGDs. The index into the user PGDs takes into account the region number,
> but the index into the kernel (init_mm) PGD always assumes a predefined
> kernel region number. Commit 974b9b2c68 ("mm: consolidate pte_index() and
> pte_offset_*() definitions") made IA-64 use a generic pgd_offset_k() which
> incorrectly used pgd_index() for kernel page tables. As a result, the
> index into the kernel PGD was going out of bounds and the kernel hung
> during early boot.
>
> Allow overrides of pgd_offset_k() and override it on IA-64 with the old
> implementation that will correctly index the kernel PGD.
>
> Fixes: 974b9b2c68 ("mm: consolidate pte_index() and pte_offset_*() definitions")
> Reported-by: John Paul Adrian Glaubitz <glaubitz@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Jessica Clarke <jrtc27@xxxxxxxxxx>
> Tested-by: John Paul Adrian Glaubitz <glaubitz@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> ---
>
> Changes since v3:
> * Correct commit message as Jessica suggested
I also corrected the comment to:
/*
* In the kernel's mapped region we know everything is in region number 5, so
* as an optimisation its PGD already points to the area for that region.
* However, this also means that we cannot use pgd_index() and we must
* never add the region here.
*/
> Changes since v2:
> * Rephrase commit message and comment about pgd_offset_k()
>
> Changes since v1:
> * Fixed typo in commit message
> * Slightly reworded commit message to sound less weird
> * Included Adrian's Tested-by
>
>
> arch/ia64/include/asm/pgtable.h | 9 +++++++++
> include/linux/pgtable.h | 2 ++
> 2 files changed, 11 insertions(+)
>
> diff --git a/arch/ia64/include/asm/pgtable.h b/arch/ia64/include/asm/pgtable.h
> index 10850897a91c..6ef501cd0166 100644
> --- a/arch/ia64/include/asm/pgtable.h
> +++ b/arch/ia64/include/asm/pgtable.h
> @@ -366,6 +366,15 @@ pgd_index (unsigned long address)
> }
> #define pgd_index pgd_index
>
> +/*
> + * In the kernel's mapped region we know everything is in region number 5, so
> + * as an optimisation its PGD already points to the area for that region.
> + * However, this also means that we cannot use pgd_index() and we never
> + * should add the region here.
> + */
> +#define pgd_offset_k(addr) \
> + (init_mm.pgd + (((addr) >> PGDIR_SHIFT) & (PTRS_PER_PGD - 1)))
> +
> /* Look up a pgd entry in the gate area. On IA-64, the gate-area
> resides in the kernel-mapped segment, hence we use pgd_offset_k()
> here. */
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index a124c21e3204..e8cbc2e795d5 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -117,7 +117,9 @@ static inline pgd_t *pgd_offset_pgd(pgd_t *pgd, unsigned long address)
> * a shortcut which implies the use of the kernel's pgd, instead
> * of a process's
> */
> +#ifndef pgd_offset_k
> #define pgd_offset_k(address) pgd_offset(&init_mm, (address))
> +#endif
>
> /*
> * In many cases it is known that a virtual address is mapped at PMD or PTE
> --
> 2.26.2
>
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