On 2025/1/6 18:34, Alexander Gordeev wrote:
On Mon, Dec 30, 2024 at 05:07:42PM +0800, Qi Zheng wrote:
The pagetable_p*_dtor() are exactly the same except for the handling of
ptlock. If we make ptlock_free() handle the case where ptdesc->ptl is
NULL and remove VM_BUG_ON_PAGE() from pmd_ptlock_free(), we can unify
pagetable_p*_dtor() into one function. Let's introduce pagetable_dtor()
to do this.
Later, pagetable_dtor() will be moved to tlb_remove_ptdesc(), so that
ptlock and page table pages can be freed together (regardless of whether
RCU is used). This prevents the use-after-free problem where the ptlock
is freed immediately but the page table pages is freed later via RCU.
Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
Originally-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
...
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 5d82f42ddd5cc..cad11fa10c192 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2992,6 +2992,15 @@ static inline bool ptlock_init(struct ptdesc *ptdesc) { return true; }
static inline void ptlock_free(struct ptdesc *ptdesc) {}
#endif /* defined(CONFIG_SPLIT_PTE_PTLOCKS) */
+static inline void pagetable_dtor(struct ptdesc *ptdesc)
+{
+ struct folio *folio = ptdesc_folio(ptdesc);
+
+ ptlock_free(ptdesc);
+ __folio_clear_pgtable(folio);
+ lruvec_stat_sub_folio(folio, NR_PAGETABLE);
+}
+
If I am not mistaken, it is just pagetable_pte_dtor() rename.
What is the point in moving the code around?
No, this is to unify pagetable_p*_dtor() into pagetable_dtor(), so
that we can move pagetable_dtor() to __tlb_remove_table(), and then
ptlock and PTE page can be freed together through RCU, which is
also the main purpose of this patch series.
Thanks!
static inline bool pagetable_pte_ctor(struct ptdesc *ptdesc)
{
struct folio *folio = ptdesc_folio(ptdesc);
@@ -3003,15 +3012,6 @@ static inline bool pagetable_pte_ctor(struct ptdesc *ptdesc)
return true;
}
-static inline void pagetable_pte_dtor(struct ptdesc *ptdesc)
-{
- struct folio *folio = ptdesc_folio(ptdesc);
-
- ptlock_free(ptdesc);
- __folio_clear_pgtable(folio);
- lruvec_stat_sub_folio(folio, NR_PAGETABLE);
-}
-
pte_t *___pte_offset_map(pmd_t *pmd, unsigned long addr, pmd_t *pmdvalp);
static inline pte_t *__pte_offset_map(pmd_t *pmd, unsigned long addr,
pmd_t *pmdvalp)
