[PATCH v2 08/15] riscv: pgtable: move pagetable_dtor() to __tlb_remove_table()

[Qi Zheng]

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@xxxxxxxxxxxxx>
Suggested-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: linux-riscv@xxxxxxxxxxxxxxxxxxx
---
 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 09c2eff571a49..fc50d14010246 100644
--- a/arch/riscv/include/asm/pgalloc.h
+++ b/arch/riscv/include/asm/pgalloc.h
@@ -18,12 +18,22 @@
 #define __HAVE_ARCH_P4D_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,
@@ -109,12 +119,8 @@ 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));
 }
 
 #define p4d_alloc_one p4d_alloc_one
@@ -136,12 +142,8 @@ static inline void p4d_free(struct mm_struct *mm, p4d_t *p4d)
 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 */
 
@@ -170,10 +172,7 @@ 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 */
@@ -181,10 +180,7 @@ 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