[PATCH v3 10/17] riscv: pgtable: move pagetable_dtor() to __tlb_remove_table()

Qi Zheng
2024-12-23T09:45:11Z

Move pagetable_dtor() to __tlb_remove_table(), 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.

Page tables shouldn't have swap cache, so use pagetable_free() instead of
free_page_and_swap_cache() to free page table pages.

By the way, move the comment above __tlb_remove_table() to
riscv_tlb_remove_ptdesc(), it will be more appropriate.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: linux-riscv@lists.infradead.org
---
arch/riscv/include/asm/pgalloc.h | 38 ++++++++++++++------------------
arch/riscv/include/asm/tlb.h | 14 ++++--------
2 files changed, 21 insertions(+), 31 deletions(-)

diff --git a/arch/riscv/include/asm/pgalloc.h b/arch/riscv/include/asm/pgalloc.h
index b6793c5c99296..c8907b8317115 100644
--- a/arch/riscv/include/asm/pgalloc.h
+++ b/arch/riscv/include/asm/pgalloc.h
@@ -15,12 +15,22 @@
#define __HAVE_ARCH_PUD_FREE
#include <asm-generic/pgalloc.h>

+/*
+ * While riscv platforms with riscv_ipi_for_rfence as true require an IPI to
+ * perform TLB shootdown, some platforms with riscv_ipi_for_rfence as false use
+ * SBI to perform TLB shootdown. To keep software pagetable walkers safe in this
+ * case we switch to RCU based table free (MMU_GATHER_RCU_TABLE_FREE). See the
+ * comment below 'ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE' in include/asm-generic/tlb.h
+ * for more details.
+ */
static inline void riscv_tlb_remove_ptdesc(struct mmu_gather *tlb, void *pt)
{
- if (riscv_use_sbi_for_rfence())
+ if (riscv_use_sbi_for_rfence()) {
tlb_remove_ptdesc(tlb, pt);
- else
+ } else {
+ pagetable_dtor(pt);
tlb_remove_page_ptdesc(tlb, pt);
+ }
}

static inline void pmd_populate_kernel(struct mm_struct *mm,
@@ -97,23 +107,15 @@ static inline void pud_free(struct mm_struct *mm, pud_t *pud)
static inline void __pud_free_tlb(struct mmu_gather *tlb, pud_t *pud,
unsigned long addr)
{
- if (pgtable_l4_enabled) {
- struct ptdesc *ptdesc = virt_to_ptdesc(pud);
-
- pagetable_dtor(ptdesc);
- riscv_tlb_remove_ptdesc(tlb, ptdesc);
- }
+ if (pgtable_l4_enabled)
+ riscv_tlb_remove_ptdesc(tlb, virt_to_ptdesc(pud));
}

static inline void __p4d_free_tlb(struct mmu_gather *tlb, p4d_t *p4d,
unsigned long addr)
{
- if (pgtable_l5_enabled) {
- struct ptdesc *ptdesc = virt_to_ptdesc(p4d);
-
- pagetable_dtor(ptdesc);
+ if (pgtable_l5_enabled)
riscv_tlb_remove_ptdesc(tlb, virt_to_ptdesc(p4d));
- }
}
#endif /* __PAGETABLE_PMD_FOLDED */

@@ -142,10 +144,7 @@ static inline pgd_t *pgd_alloc(struct mm_struct *mm)
static inline void __pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmd,
unsigned long addr)
{
- struct ptdesc *ptdesc = virt_to_ptdesc(pmd);
-
- pagetable_dtor(ptdesc);
- riscv_tlb_remove_ptdesc(tlb, ptdesc);
+ riscv_tlb_remove_ptdesc(tlb, virt_to_ptdesc(pmd));
}

#endif /* __PAGETABLE_PMD_FOLDED */
@@ -153,10 +152,7 @@ static inline void __pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmd,
static inline void __pte_free_tlb(struct mmu_gather *tlb, pgtable_t pte,
unsigned long addr)
{
- struct ptdesc *ptdesc = page_ptdesc(pte);
-
- pagetable_dtor(ptdesc);
- riscv_tlb_remove_ptdesc(tlb, ptdesc);
+ riscv_tlb_remove_ptdesc(tlb, page_ptdesc(pte));
}
#endif /* CONFIG_MMU */

diff --git a/arch/riscv/include/asm/tlb.h b/arch/riscv/include/asm/tlb.h
index 1f6c38420d8e0..ded8724b3c4f7 100644
--- a/arch/riscv/include/asm/tlb.h
+++ b/arch/riscv/include/asm/tlb.h
@@ -11,19 +11,13 @@ struct mmu_gather;
static void tlb_flush(struct mmu_gather *tlb);

#ifdef CONFIG_MMU
-#include <linux/swap.h>

-/*
- * While riscv platforms with riscv_ipi_for_rfence as true require an IPI to
- * perform TLB shootdown, some platforms with riscv_ipi_for_rfence as false use
- * SBI to perform TLB shootdown. To keep software pagetable walkers safe in this
- * case we switch to RCU based table free (MMU_GATHER_RCU_TABLE_FREE). See the
- * comment below 'ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE' in include/asm-generic/tlb.h
- * for more details.
- */
static inline void __tlb_remove_table(void *table)
{
- free_page_and_swap_cache(table);
+ struct ptdesc *ptdesc = (struct ptdesc *)table;
+
+ pagetable_dtor(ptdesc);
+ pagetable_free(ptdesc);
}

#endif /* CONFIG_MMU */
--
2.20.1