From patchwork series 523109

https://patchwork.ozlabs.org//project/linuxppc-dev/list/?series=523109

Author: Fox Snowpatch

Documentation/mm/process_addrs.rst

@@ -537,6 +537,12 @@ We establish basic locking rules when interacting with page tables:
 * When changing a page table entry the page table lock for that page table
   **must** be held, except if you can safely assume nobody can access the page
   tables concurrently (such as on invocation of :c:func:`!free_pgtables`).
+* Page tables may be *walked* under RCU alone, as page tables are freed only
+  after an RCU grace period has elapsed. However, any entry found must be
+  revalidated after the page table lock is taken (such as the
+  :c:func:`!pmd_same` recheck performed by :c:func:`!pte_offset_map_lock`)
+  before it is acted upon. Changing an entry requires the page table
+  lock and one of the locks that excludes teardown (mmap or VMA lock).
 * Reads from and writes to page table entries must be *appropriately*
   atomic. See the section on atomicity below for details.
 * Populating previously empty entries requires that the mmap or VMA locks are

arch/Kconfig

@@ -526,13 +526,6 @@ config HAVE_ARCH_JUMP_LABEL
 config HAVE_ARCH_JUMP_LABEL_RELATIVE
 	bool
 
-config MMU_GATHER_TABLE_FREE
-	bool
-
-config MMU_GATHER_RCU_TABLE_FREE
-	bool
-	select MMU_GATHER_TABLE_FREE
-
 config MMU_GATHER_PAGE_SIZE
 	bool
 
@@ -548,7 +541,6 @@ config MMU_GATHER_MERGE_VMAS
 
 config MMU_GATHER_NO_GATHER
 	bool
-	depends on MMU_GATHER_TABLE_FREE
 
 config ARCH_WANT_IRQS_OFF_ACTIVATE_MM
 	bool

arch/alpha/Kconfig

@@ -42,7 +42,6 @@ config ALPHA
 	select ARCH_STACKWALK
 	select CPU_NO_EFFICIENT_FFS if !ALPHA_EV67
 	select MMU_GATHER_NO_RANGE
-	select MMU_GATHER_RCU_TABLE_FREE
 	select SPARSEMEM_EXTREME if SPARSEMEM
 	select ZONE_DMA
 	select TRACE_IRQFLAGS_SUPPORT

arch/arc/include/asm/pgalloc.h

@@ -72,7 +72,7 @@ static inline void p4d_populate(struct mm_struct *mm, p4d_t *p4dp, pud_t *pudp)
 	set_p4d(p4dp, __p4d((unsigned long)pudp));
 }
 
-#define __pud_free_tlb(tlb, pmd, addr)  pud_free((tlb)->mm, pmd)
+#define __pud_free_tlb(tlb, pmd, addr)  tlb_remove_ptdesc((tlb), virt_to_ptdesc(pmd))
 
 #endif
 
@@ -83,10 +83,10 @@ static inline void pud_populate(struct mm_struct *mm, pud_t *pudp, pmd_t *pmdp)
 	set_pud(pudp, __pud((unsigned long)pmdp));
 }
 
-#define __pmd_free_tlb(tlb, pmd, addr)  pmd_free((tlb)->mm, pmd)
+#define __pmd_free_tlb(tlb, pmd, addr)  tlb_remove_ptdesc((tlb), virt_to_ptdesc(pmd))
 
 #endif
 
-#define __pte_free_tlb(tlb, pte, addr)  pte_free((tlb)->mm, pte)
+#define __pte_free_tlb(tlb, pte, addr)  tlb_remove_ptdesc((tlb), page_ptdesc(pte))
 
 #endif /* _ASM_ARC_PGALLOC_H */

arch/arm/Kconfig

@@ -135,7 +135,6 @@ config ARM
 	select HAVE_PERF_REGS
 	select HAVE_PERF_USER_STACK_DUMP
 	select HAVE_POSIX_CPU_TIMERS_TASK_WORK
-	select MMU_GATHER_RCU_TABLE_FREE if SMP && ARM_LPAE
 	select HAVE_REGS_AND_STACK_ACCESS_API
 	select HAVE_RSEQ
 	select HAVE_RUST if CPU_LITTLE_ENDIAN && CPU_32v7 && !KASAN

arch/arm64/Kconfig

@@ -222,7 +222,6 @@ config ARM64
 	select HAVE_RELIABLE_STACKTRACE
 	select HAVE_POSIX_CPU_TIMERS_TASK_WORK
 	select HAVE_FUNCTION_ARG_ACCESS_API
-	select MMU_GATHER_RCU_TABLE_FREE
 	select HAVE_RSEQ
 	select HAVE_RUST if RUSTC_SUPPORTS_ARM64
 	select HAVE_STACKPROTECTOR

arch/loongarch/Kconfig

@@ -189,7 +189,6 @@ config LOONGARCH
 	select IRQ_LOONGARCH_CPU
 	select LOCK_MM_AND_FIND_VMA
 	select MMU_GATHER_MERGE_VMAS if MMU
-	select MMU_GATHER_RCU_TABLE_FREE
 	select MODULES_USE_ELF_RELA if MODULES
 	select NEED_PER_CPU_EMBED_FIRST_CHUNK
 	select NEED_PER_CPU_PAGE_FIRST_CHUNK

arch/m68k/Kconfig

@@ -29,6 +29,7 @@ config M68K
 	select HAVE_ARCH_LIBGCC_H
 	select HAVE_ARCH_SECCOMP
 	select HAVE_ARCH_SECCOMP_FILTER
+	select HAVE_ARCH_TLB_REMOVE_TABLE if MMU_MOTOROLA
 	select HAVE_ASM_MODVERSIONS
 	select HAVE_DEBUG_BUGVERBOSE
 	select HAVE_EFFICIENT_UNALIGNED_ACCESS if !CPU_HAS_NO_UNALIGNED

arch/m68k/include/asm/mcf_pgalloc.h

@@ -39,10 +39,7 @@ extern inline pmd_t *pmd_alloc_kernel(pgd_t *pgd, unsigned long address)
 static inline void __pte_free_tlb(struct mmu_gather *tlb, pgtable_t pgtable,
 				  unsigned long address)
 {
-	struct ptdesc *ptdesc = virt_to_ptdesc(pgtable);
-
-	pagetable_dtor(ptdesc);
-	pagetable_free(ptdesc);
+	tlb_remove_ptdesc(tlb, virt_to_ptdesc(pgtable));
 }
 
 static inline pgtable_t pte_alloc_one(struct mm_struct *mm)

arch/m68k/include/asm/motorola_pgalloc.h

@@ -17,6 +17,7 @@ enum m68k_table_types {
 extern void init_pointer_table(void *table, int type);
 extern void *get_pointer_table(struct mm_struct *mm, int type);
 extern int free_pointer_table(void *table, int type);
+extern void __tlb_remove_table(void *table);
 
 /*
  * Allocate and free page tables. The xxx_kernel() versions are
@@ -47,7 +48,7 @@ static inline void pte_free(struct mm_struct *mm, pgtable_t pgtable)
 static inline void __pte_free_tlb(struct mmu_gather *tlb, pgtable_t pgtable,
 				  unsigned long address)
 {
-	free_pointer_table(pgtable, TABLE_PTE);
+	tlb_remove_table(tlb, (void *)((unsigned long)pgtable | TABLE_PTE));
 }
 
 
@@ -61,10 +62,10 @@ static inline int pmd_free(struct mm_struct *mm, pmd_t *pmd)
 	return free_pointer_table(pmd, TABLE_PMD);
 }
 
-static inline int __pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmd,
-				 unsigned long address)
+static inline void __pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmd,
+				  unsigned long address)
 {
-	return free_pointer_table(pmd, TABLE_PMD);
+	tlb_remove_table(tlb, (void *)((unsigned long)pmd | TABLE_PMD));
 }