On Fri, Sep 15, 2023 at 10:59:21AM +0000, Matteo Rizzo wrote:
> From: Jann Horn <jannh@xxxxxxxxxx>
>
> This is refactoring in preparation for adding two different
> implementations (for SLAB_VIRTUAL enabled and disabled).
>
> virt_to_folio(x) expands to _compound_head(virt_to_page(x)) and
> virt_to_head_page(x) also expands to _compound_head(virt_to_page(x))
>
> so PageSlab(virt_to_head_page(res)) should be equivalent to
> is_slab_addr(res).
Perhaps add a note that redundant calls to virt_to_folio() will be
removed in following patches?
>
> Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
> Co-developed-by: Matteo Rizzo <matteorizzo@xxxxxxxxxx>
> Signed-off-by: Matteo Rizzo <matteorizzo@xxxxxxxxxx>
> ---
> include/linux/slab.h | 1 +
> kernel/resource.c | 2 +-
> mm/slab.h | 9 +++++++++
> mm/slab_common.c | 5 ++---
> mm/slub.c | 6 +++---
> 5 files changed, 16 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index 8228d1276a2f..a2d82010d269 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -793,4 +793,5 @@ int slab_dead_cpu(unsigned int cpu);
> #define slab_dead_cpu NULL
> #endif
>
> +#define is_slab_addr(addr) folio_test_slab(virt_to_folio(addr))
> #endif /* _LINUX_SLAB_H */
> diff --git a/kernel/resource.c b/kernel/resource.c
> index b1763b2fd7ef..c829e5f97292 100644
> --- a/kernel/resource.c
> +++ b/kernel/resource.c
> @@ -158,7 +158,7 @@ static void free_resource(struct resource *res)
> * buddy and trying to be smart and reusing them eventually in
> * alloc_resource() overcomplicates resource handling.
> */
> - if (res && PageSlab(virt_to_head_page(res)))
> + if (res && is_slab_addr(res))
> kfree(res);
> }
>
> diff --git a/mm/slab.h b/mm/slab.h
> index 799a315695c6..25e41dd6087e 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -169,6 +169,15 @@ static_assert(IS_ALIGNED(offsetof(struct slab, freelist), sizeof(freelist_aba_t)
> */
> #define slab_page(s) folio_page(slab_folio(s), 0)
>
> +/**
> + * is_slab_page - Checks if a page is really a slab page
> + * @s: The slab
> + *
> + * Checks if s points to a slab page.
> + *
> + * Return: true if s points to a slab and false otherwise.
> + */
> +#define is_slab_page(s) folio_test_slab(slab_folio(s))
> /*
> * If network-based swap is enabled, sl*b must keep track of whether pages
> * were allocated from pfmemalloc reserves.
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index e99e821065c3..79102d24f099 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -1063,7 +1063,7 @@ void kfree(const void *object)
> return;
>
> folio = virt_to_folio(object);
> - if (unlikely(!folio_test_slab(folio))) {
> + if (unlikely(!is_slab_addr(object))) {
> free_large_kmalloc(folio, (void *)object);
> return;
> }
> @@ -1094,8 +1094,7 @@ size_t __ksize(const void *object)
> return 0;
>
> folio = virt_to_folio(object);
> -
> - if (unlikely(!folio_test_slab(folio))) {
> + if (unlikely(!is_slab_addr(object))) {
> if (WARN_ON(folio_size(folio) <= KMALLOC_MAX_CACHE_SIZE))
> return 0;
> if (WARN_ON(object != folio_address(folio)))
In the above 2 hunks we're doing virt_to_folio() twice, but I see in
patch 4 that these go away.
> diff --git a/mm/slub.c b/mm/slub.c
> index a7dae207c2d2..b69916ab7aa8 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1259,7 +1259,7 @@ static int check_slab(struct kmem_cache *s, struct slab *slab)
> {
> int maxobj;
>
> - if (!folio_test_slab(slab_folio(slab))) {
> + if (!is_slab_page(slab)) {
> slab_err(s, slab, "Not a valid slab page");
> return 0;
> }
> @@ -1454,7 +1454,7 @@ static noinline bool alloc_debug_processing(struct kmem_cache *s,
> return true;
>
> bad:
> - if (folio_test_slab(slab_folio(slab))) {
> + if (is_slab_page(slab)) {
> /*
> * If this is a slab page then lets do the best we can
> * to avoid issues in the future. Marking all objects
> @@ -1484,7 +1484,7 @@ static inline int free_consistency_checks(struct kmem_cache *s,
> return 0;
>
> if (unlikely(s != slab->slab_cache)) {
> - if (!folio_test_slab(slab_folio(slab))) {
> + if (!is_slab_page(slab)) {
> slab_err(s, slab, "Attempt to free object(0x%p) outside of slab",
> object);
> } else if (!slab->slab_cache) {
> --
> 2.42.0.459.ge4e396fd5e-goog
This all looks nice and mechanical. :P
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
--
Kees Cook
