[PATCH 09/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for m68k-motorola
From: Lorenzo Stoakes (ARM)
Date: Tue Sep 01 2026 - 07:11:37 EST
sun3 and coldfire are already supported, however motorola requires a little
more care.
Here, custom table removal logic is required, so
CONFIG_HAVE_ARCH_TLB_REMOVE_TABLE is enabled for m68k-motorola.
Firstly as part of this change, the page table level must be communicated
to the underlying __tlb_remove_table() implementation.
Take advantage of the fact that page tables are aligned by more than enough
to permit setting TABLE_PTE or TABLE_PMD in the low bits of the pointer,
and store this there.
Then update __pte_free_tlb() and __pmd_free_tlb() to pass this through,
then have __tlb_remove_table() decode this and pass it to
free_pointer_table().
The page table freeing is performed via call_rcu(), so free_pointer_table()
now will be invoked from softirq context, and as such may be re-entrant.
Introduce an irq save/restore spinlock to handle this, and hold it over the
time a given ptable entry is being referenced in both get_pointer_table()
and free_pointer_table().
In order to make things a little easier in this respect, separate out the
logic for adding a new ptable entry into add_pointer_table() and only hold
the lock during ptable entry insertion in this case.
Note that original list_add_tail(new, dp) added new prior to dp, which is
ptable_list[type].next, i.e. after ptable_list[type].
The equivalent therefore is list_add(new, &ptable_list[type]), which adds
new after ptable_list[type], only without needing to make reference to dp.
Note that, as m68k-motorola specifies CONFIG_HAVE_ARCH_TLB_REMOVE_TABLE, it
does not enable CONFIG_PT_RECLAIM. This isn't meaningfully impactful.
With this applied, all of m68k implements CONFIG_MMU_GATHER_RCU_TABLE_FREE.
This forms part of an overall effort to switch every architecture to this
mode.
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx>
---
arch/m68k/Kconfig | 3 +-
arch/m68k/include/asm/motorola_pgalloc.h | 9 ++-
arch/m68k/mm/motorola.c | 121 ++++++++++++++++++++-----------
3 files changed, 86 insertions(+), 47 deletions(-)
diff --git a/arch/m68k/Kconfig b/arch/m68k/Kconfig
index 6b8ec67c86fd..fa5d39549da9 100644
--- a/arch/m68k/Kconfig
+++ b/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
@@ -36,7 +37,7 @@ config M68K
select HAVE_MOD_ARCH_SPECIFIC
select HAVE_UID16
select MMU_GATHER_NO_RANGE if MMU
- select MMU_GATHER_RCU_TABLE_FREE if MMU && (SUN3 || COLDFIRE)
+ select MMU_GATHER_RCU_TABLE_FREE if MMU
select MODULES_USE_ELF_REL
select MODULES_USE_ELF_RELA
select NO_DMA if !MMU && !COLDFIRE
diff --git a/arch/m68k/include/asm/motorola_pgalloc.h b/arch/m68k/include/asm/motorola_pgalloc.h
index 1091fb0affbe..dcde40e8b5c6 100644
--- a/arch/m68k/include/asm/motorola_pgalloc.h
+++ b/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));
}
diff --git a/arch/m68k/mm/motorola.c b/arch/m68k/mm/motorola.c
index b30aa69a73a6..ffc80483440b 100644
--- a/arch/m68k/mm/motorola.c
+++ b/arch/m68k/mm/motorola.c
@@ -20,6 +20,7 @@
#include <linux/init.h>
#include <linux/memblock.h>
#include <linux/gfp.h>
+#include <linux/cleanup.h>
#include <asm/setup.h>
#include <linux/uaccess.h>
@@ -103,6 +104,8 @@ static struct list_head ptable_list[3] = {
LIST_HEAD_INIT(ptable_list[2]),
};
+static DEFINE_SPINLOCK(ptable_lock);
+
#define PD_PTABLE(ptdesc) ((ptable_desc *)&(virt_to_ptdesc((void *)(ptdesc))->pt_list))
#define PD_PTDESC(ptable) (list_entry(ptable, struct ptdesc, pt_list))
#define PD_MARKBITS(dp) (*(unsigned int *)&PD_PTDESC(dp)->pt_index)
@@ -139,52 +142,66 @@ void __init init_pointer_table(void *table, int type)
return;
}
-void *get_pointer_table(struct mm_struct *mm, int type)
+/*
+ * For a pointer table for a user process address space, a
+ * table is taken from a ptdesc allocated for the purpose. Each
+ * ptdesc can hold 8 pointer tables. The ptdesc is remapped in
+ * virtual address space to be noncacheable.
+ */
+static void *add_pointer_table(struct mm_struct *mm, int type)
{
- ptable_desc *dp = ptable_list[type].next;
- unsigned int mask = list_empty(&ptable_list[type]) ? 0 : PD_MARKBITS(dp);
- unsigned int tmp, off;
+ struct ptdesc *ptdesc;
+ ptable_desc *new;
+ void *pt_addr;
- /*
- * For a pointer table for a user process address space, a
- * table is taken from a ptdesc allocated for the purpose. Each
- * ptdesc can hold 8 pointer tables. The ptdesc is remapped in
- * virtual address space to be noncacheable.
- */
- if (mask == 0) {
- struct ptdesc *ptdesc;
- ptable_desc *new;
- void *pt_addr;
-
- ptdesc = pagetable_alloc(GFP_KERNEL | __GFP_ZERO, 0);
- if (!ptdesc)
- return NULL;
-
- pt_addr = ptdesc_address(ptdesc);
-
- switch (type) {
- case TABLE_PTE:
- /*
- * m68k doesn't have SPLIT_PTE_PTLOCKS for not having
- * SMP.
- */
- pagetable_pte_ctor(mm, ptdesc);
- break;
- case TABLE_PMD:
- pagetable_pmd_ctor(mm, ptdesc);
- break;
- case TABLE_PGD:
- pagetable_pgd_ctor(ptdesc);
- break;
- }
+ ptdesc = pagetable_alloc(GFP_KERNEL | __GFP_ZERO, 0);
+ if (!ptdesc)
+ return NULL;
+
+ pt_addr = ptdesc_address(ptdesc);
+
+ switch (type) {
+ case TABLE_PTE:
+ /*
+ * m68k doesn't have SPLIT_PTE_PTLOCKS for not having
+ * SMP.
+ */
+ pagetable_pte_ctor(mm, ptdesc);
+ break;
+ case TABLE_PMD:
+ pagetable_pmd_ctor(mm, ptdesc);
+ break;
+ case TABLE_PGD:
+ pagetable_pgd_ctor(ptdesc);
+ break;
+ }
+
+ mmu_page_ctor(pt_addr);
+
+ new = PD_PTABLE(pt_addr);
- mmu_page_ctor(pt_addr);
+ PD_MARKBITS(new) = ptable_mask(type) - 1;
+ scoped_guard(spinlock_irqsave, &ptable_lock)
+ list_add(new, &ptable_list[type]);
- new = PD_PTABLE(pt_addr);
- PD_MARKBITS(new) = ptable_mask(type) - 1;
- list_add_tail(new, dp);
+ return (pmd_t *)pt_addr;
+}
+
+void *get_pointer_table(struct mm_struct *mm, int type)
+{
+ unsigned int tmp, off;
+ unsigned long mask;
+ unsigned long flags;
+ ptable_desc *dp;
+ void *ret;
- return (pmd_t *)pt_addr;
+ spin_lock_irqsave(&ptable_lock, flags);
+ dp = ptable_list[type].next;
+ mask = list_empty(&ptable_list[type]) ? 0 : PD_MARKBITS(dp);
+
+ if (mask == 0) {
+ spin_unlock_irqrestore(&ptable_lock, flags);
+ return add_pointer_table(mm, type);
}
for (tmp = 1, off = 0; (mask & tmp) == 0; tmp <<= 1, off += ptable_size(type))
@@ -194,7 +211,10 @@ void *get_pointer_table(struct mm_struct *mm, int type)
/* move to end of list */
list_move_tail(dp, &ptable_list[type]);
}
- return ptdesc_address(PD_PTDESC(dp)) + off;
+
+ ret = ptdesc_address(PD_PTDESC(dp)) + off;
+ spin_unlock_irqrestore(&ptable_lock, flags);
+ return ret;
}
int free_pointer_table(void *table, int type)
@@ -203,6 +223,9 @@ int free_pointer_table(void *table, int type)
unsigned long ptable = (unsigned long)table;
unsigned long pt_addr = ptable & PAGE_MASK;
unsigned int mask = 1U << ((ptable - pt_addr)/ptable_size(type));
+ unsigned long flags;
+
+ spin_lock_irqsave(&ptable_lock, flags);
dp = PD_PTABLE(pt_addr);
if (PD_MARKBITS (dp) & mask)
@@ -213,6 +236,8 @@ int free_pointer_table(void *table, int type)
if (PD_MARKBITS(dp) == ptable_mask(type)) {
/* all tables in ptdesc are free, free ptdesc */
list_del(dp);
+ spin_unlock_irqrestore(&ptable_lock, flags);
+
mmu_page_dtor((void *)pt_addr);
pagetable_dtor_free(virt_to_ptdesc((void *)pt_addr));
return 1;
@@ -223,9 +248,21 @@ int free_pointer_table(void *table, int type)
*/
list_move(dp, &ptable_list[type]);
}
+
+ spin_unlock_irqrestore(&ptable_lock, flags);
return 0;
}
+void __tlb_remove_table(void *table)
+{
+ /* The bottom 2 bits are used to encode page table type. */
+ const unsigned long encoded = (unsigned long)table;
+ void *addr = (void *)(encoded & ~3UL);
+ const int type = encoded & 3;
+
+ free_pointer_table(addr, type);
+}
+
/* size of memory already mapped in head.S */
extern __initdata unsigned long m68k_init_mapped_size;
--
2.55.0