Re: [PATCH v2 13/22] alpha: add ARCH_SUPPORTS_PAGE_TABLE_CHECK support

[Magnus Lindholm]

Hi Matt,

On Sat, Sep 5, 2026 at 9:29 PM Matt Turner <mattst88@xxxxxxxxx> wrote:
>
> Add the page table check helpers needed for CONFIG_PAGE_TABLE_CHECK
> and select ARCH_SUPPORTS_PAGE_TABLE_CHECK in Kconfig.
>
> Alpha does not support huge pages, so pmd_user_accessible_page() and
> pud_user_accessible_page() always return false. pte_user_accessible_page()
> checks for present PTEs with user read access (_PAGE_URE).
>
> Assisted-by: Claude:claude-opus-4-6
> Signed-off-by: Matt Turner <mattst88@xxxxxxxxx>
>
> Update the helpers to the three-argument pxx_user_accessible_page(mm,
> addr, pxx) signature introduced by commit cf8771ca4cdb ("mm/page_table_check:
> Pass mm_struct to pxx_user_accessible_page()"), matching the other
> architectures.
> ---
>  arch/alpha/Kconfig               |  1 +
>  arch/alpha/include/asm/pgtable.h | 19 +++++++++++++++++++
>  2 files changed, 20 insertions(+)
>
> diff --git a/arch/alpha/Kconfig b/arch/alpha/Kconfig
> index 1d28fa8d3b66..da4ec8399517 100644
> --- a/arch/alpha/Kconfig
> +++ b/arch/alpha/Kconfig
> @@ -19,6 +19,7 @@ config ALPHA
>         select ARCH_NO_SG_CHAIN
>         select ARCH_SUPPORTS_ATOMIC_RMW
>         select ARCH_SUPPORTS_INT128 if CC_HAS_INT128
> +       select ARCH_SUPPORTS_PAGE_TABLE_CHECK
>         select ARCH_USE_CMPXCHG_LOCKREF
>         select FORCE_PCI
>         select PCI_DOMAINS if PCI
> diff --git a/arch/alpha/include/asm/pgtable.h b/arch/alpha/include/asm/pgtable.h
> index bdff33b505bc..6ebdd90f3035 100644
> --- a/arch/alpha/include/asm/pgtable.h
> +++ b/arch/alpha/include/asm/pgtable.h
> @@ -232,6 +232,25 @@ extern inline void pud_clear(pud_t * pudp) { pud_val(*pudp) = 0; }
>  extern inline int pte_write(pte_t pte)         { return !(pte_val(pte) & _PAGE_FOW); }
>  extern inline int pte_dirty(pte_t pte)         { return pte_val(pte) & _PAGE_DIRTY; }
>  extern inline int pte_young(pte_t pte)         { return pte_val(pte) & _PAGE_ACCESSED; }
> +extern inline int pte_user(pte_t pte)          { return pte_val(pte) & _PAGE_URE; }
> +
> +static inline bool pte_user_accessible_page(struct mm_struct *mm,
> +                                            unsigned long addr, pte_t pte)
> +{
> +       return pte_present(pte) && pte_user(pte);
> +}
> +
> +static inline bool pmd_user_accessible_page(struct mm_struct *mm,
> +                                            unsigned long addr, pmd_t pmd)
> +{
> +       return false;
> +}
> +
> +static inline bool pud_user_accessible_page(struct mm_struct *mm,
> +                                            unsigned long addr, pud_t pud)
> +{
> +       return false;
> +}
>
>  extern inline pte_t pte_wrprotect(pte_t pte)   { pte_val(pte) |= _PAGE_FOW; return pte; }
>  extern inline pte_t pte_mkclean(pte_t pte)     { pte_val(pte) &= ~(__DIRTY_BITS); return pte; }
>
Hi Matt,

I tested this on a two-CPU UP2000 with PAGE_TABLE_CHECK enabled and
enforced. A userspace test exercised anonymous, private file-backed,
and shared mappings, together with fork/COW, mprotect(), madvise(),
PTE teardown, and refault.

Single-process and concurrent CPU-pinned runs completed successfully,
with no page-table-check warnings, BUGs, or oopses.

Tested-by: Magnus Lindholm <linmag7@xxxxxxxxx>
Reviewed-by: Magnus Lindholm <linmag7@xxxxxxxxx>

Regards,
Magnus