On Thu, May 18, 2023 at 12:07:26PM +0100, Ryan Roberts wrote:
> There are many call sites that directly dereference a pte_t pointer.
> This makes it very difficult to properly encapsulate a page table in the
> arch code without having to allocate shadow page tables. ptep_deref()
> aims to solve this by replacing all direct dereferences with a call to
> this function.
>
> The default implementation continues to just dereference the pointer
> (*ptep), so generated code should be exactly the same. However, it is
> possible for the architecture to override the default with their own
> implementation, that can (e.g.) hide certain bits from the core code, or
> determine young/dirty status by mixing in state from another source.
>
> While ptep_get() and ptep_get_lockless() already exist, these are
> implemented as atomic accesses (e.g. READ_ONCE() in the default case).
> So rather than using ptep_get() and risking performance regressions,
> introduce an new variant.
>
> Call sites will be converted to use the accessor in future commits.
>
> Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx>
> ---
> include/linux/pgtable.h | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index c5a51481bbb9..1161beab2492 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -204,6 +204,13 @@ static inline int pudp_set_access_flags(struct vm_area_struct *vma,
> #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
> #endif
>
> +#ifndef ptep_deref
> +static inline pte_t ptep_deref(pte_t *ptep)
> +{
> + return *(pte_t *)ptep;
Why do you need the casting here?
> +}
> +#endif
> +
> #ifndef __HAVE_ARCH_PTEP_TEST_AND_CLEAR_YOUNG
> static inline int ptep_test_and_clear_young(struct vm_area_struct *vma,
> unsigned long address,
> --
> 2.25.1
>
>
--
Sincerely yours,
Mike.
