mm: turn USE_SPLIT_PTE_PTLOCKS / USE_SPLIT_PTE_PTLOCKS into Kconfig options

Patch series "mm: split PTE/PMD PT table Kconfig cleanups+clarifications".

This series is a follow up to the fixes:
	"[PATCH v1 0/2] mm/hugetlb: fix hugetlb vs. core-mm PT locking"

When working on the fixes, I wondered why 8xx is fine (-> never uses split
PT locks) and how PT locking even works properly with PMD page table
sharing (-> always requires split PMD PT locks).

Let's improve the split PT lock detection, make hugetlb properly depend on
it and make 8xx bail out if it would ever get enabled by accident.

As an alternative to patch #3 we could extend the Kconfig
SPLIT_PTE_PTLOCKS option from patch #2 -- but enforcing it closer to the
code that actually implements it feels a bit nicer for documentation
purposes, and there is no need to actually disable it because it should
always be disabled (!SMP).

Did a bunch of cross-compilations to make sure that split PTE/PMD PT locks
are still getting used where we would expect them.

[1] https://lkml.kernel.org/r/20240725183955.2268884-1-david@redhat.com

This patch (of 3):

Let's clean that up a bit and prepare for depending on
CONFIG_SPLIT_PMD_PTLOCKS in other Kconfig options.

More cleanups would be reasonable (like the arch-specific "depends on" for
CONFIG_SPLIT_PTE_PTLOCKS), but we'll leave that for another day.

Link: https://lkml.kernel.org/r/20240726150728.3159964-1-david@redhat.com
Link: https://lkml.kernel.org/r/20240726150728.3159964-2-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Peter Xu <peterx@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/arch/arm/mm/fault-armv.c b/arch/arm/mm/fault-armv.c
index 2286c2ea60ec48934c4b72971d011ca182775b66..831793cd6ff944358508e455fe1c642ef325905b 100644 (file)
--- a/arch/arm/mm/fault-armv.c
+++ b/arch/arm/mm/fault-armv.c
@@ -61,7 +61,7 @@ static int do_adjust_pte(struct vm_area_struct *vma, unsigned long address,
        return ret;
 }
 
-#if USE_SPLIT_PTE_PTLOCKS
+#if defined(CONFIG_SPLIT_PTE_PTLOCKS)
 /*
  * If we are using split PTE locks, then we need to take the page
  * lock here.  Otherwise we are using shared mm->page_table_lock
@@ -80,10 +80,10 @@ static inline void do_pte_unlock(spinlock_t *ptl)
 {
        spin_unlock(ptl);
 }
-#else /* !USE_SPLIT_PTE_PTLOCKS */
+#else /* !defined(CONFIG_SPLIT_PTE_PTLOCKS) */
 static inline void do_pte_lock(spinlock_t *ptl) {}
 static inline void do_pte_unlock(spinlock_t *ptl) {}
-#endif /* USE_SPLIT_PTE_PTLOCKS */
+#endif /* defined(CONFIG_SPLIT_PTE_PTLOCKS) */
 
 static int adjust_pte(struct vm_area_struct *vma, unsigned long address,
        unsigned long pfn)

diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c
index f1ce39d6d32cbb60a8d19a8efd5d4b358a6e24b6..f4a316894bbb42e20dbc89f1e10cd7ce6a95bdb8 100644 (file)
--- a/arch/x86/xen/mmu_pv.c
+++ b/arch/x86/xen/mmu_pv.c
@@ -665,7 +665,7 @@ static spinlock_t *xen_pte_lock(struct page *page, struct mm_struct *mm)
 {
        spinlock_t *ptl = NULL;
 
-#if USE_SPLIT_PTE_PTLOCKS
+#if defined(CONFIG_SPLIT_PTE_PTLOCKS)
        ptl = ptlock_ptr(page_ptdesc(page));
        spin_lock_nest_lock(ptl, &mm->page_table_lock);
 #endif
@@ -1553,7 +1553,8 @@ static inline void xen_alloc_ptpage(struct mm_struct *mm, unsigned long pfn,
 
                __set_pfn_prot(pfn, PAGE_KERNEL_RO);
 
-               if (level == PT_PTE && USE_SPLIT_PTE_PTLOCKS && !pinned)
+               if (level == PT_PTE && IS_ENABLED(CONFIG_SPLIT_PTE_PTLOCKS) &&
+                   !pinned)
                        __pin_pagetable_pfn(MMUEXT_PIN_L1_TABLE, pfn);
 
                xen_mc_issue(XEN_LAZY_MMU);
@@ -1581,7 +1582,7 @@ static inline void xen_release_ptpage(unsigned long pfn, unsigned level)
        if (pinned) {
                xen_mc_batch();
 
-               if (level == PT_PTE && USE_SPLIT_PTE_PTLOCKS)
+               if (level == PT_PTE && IS_ENABLED(CONFIG_SPLIT_PTE_PTLOCKS))
                        __pin_pagetable_pfn(MMUEXT_UNPIN_TABLE, pfn);
 
                __set_pfn_prot(pfn, PAGE_KERNEL);

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 6c2078ca3391452b3ab73eab69f2b49b873a1bc1..b7000fa300f35fedd60892a95098cd3ebbee635d 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2891,7 +2891,7 @@ static inline void pagetable_free(struct ptdesc *pt)
        __free_pages(page, compound_order(page));
 }
 
-#if USE_SPLIT_PTE_PTLOCKS
+#if defined(CONFIG_SPLIT_PTE_PTLOCKS)
 #if ALLOC_SPLIT_PTLOCKS
 void __init ptlock_cache_init(void);
 bool ptlock_alloc(struct ptdesc *ptdesc);
@@ -2949,7 +2949,7 @@ static inline bool ptlock_init(struct ptdesc *ptdesc)
        return true;
 }
 
-#else  /* !USE_SPLIT_PTE_PTLOCKS */
+#else  /* !defined(CONFIG_SPLIT_PTE_PTLOCKS) */
 /*
  * We use mm->page_table_lock to guard all pagetable pages of the mm.
  */
@@ -2964,7 +2964,7 @@ static inline spinlock_t *ptep_lockptr(struct mm_struct *mm, pte_t *pte)
 static inline void ptlock_cache_init(void) {}
 static inline bool ptlock_init(struct ptdesc *ptdesc) { return true; }
 static inline void ptlock_free(struct ptdesc *ptdesc) {}
-#endif /* USE_SPLIT_PTE_PTLOCKS */
+#endif /* defined(CONFIG_SPLIT_PTE_PTLOCKS) */
 
 static inline bool pagetable_pte_ctor(struct ptdesc *ptdesc)
 {
@@ -3024,7 +3024,7 @@ pte_t *pte_offset_map_nolock(struct mm_struct *mm, pmd_t *pmd,
        ((unlikely(pmd_none(*(pmd))) && __pte_alloc_kernel(pmd))? \
                NULL: pte_offset_kernel(pmd, address))
 
-#if USE_SPLIT_PMD_PTLOCKS
+#if defined(CONFIG_SPLIT_PMD_PTLOCKS)
 
 static inline struct page *pmd_pgtable_page(pmd_t *pmd)
 {

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 4854249792545d11db8f277dfaba223e529dfaaf..165c58b12ccc90adc5d2fa2e381a93b64ddb3d0b 100644 (file)
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -947,7 +947,7 @@ struct mm_struct {
 #ifdef CONFIG_MMU_NOTIFIER
                struct mmu_notifier_subscriptions *notifier_subscriptions;
 #endif
-#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
+#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !defined(CONFIG_SPLIT_PMD_PTLOCKS)
                pgtable_t pmd_huge_pte; /* protected by page_table_lock */
 #endif
 #ifdef CONFIG_NUMA_BALANCING

diff --git a/include/linux/mm_types_task.h b/include/linux/mm_types_task.h
index a2f6179b672b83ded2e7f64c38accd51a860e57f..bff5706b76e14f71d238ebacbe8f49e36c1bd272 100644 (file)
--- a/include/linux/mm_types_task.h
+++ b/include/linux/mm_types_task.h
@@ -16,9 +16,6 @@
 #include <asm/tlbbatch.h>
 #endif
 
-#define USE_SPLIT_PTE_PTLOCKS  (NR_CPUS >= CONFIG_SPLIT_PTLOCK_CPUS)
-#define USE_SPLIT_PMD_PTLOCKS  (USE_SPLIT_PTE_PTLOCKS && \
-               IS_ENABLED(CONFIG_ARCH_ENABLE_SPLIT_PMD_PTLOCK))
 #define ALLOC_SPLIT_PTLOCKS    (SPINLOCK_SIZE > BITS_PER_LONG/8)
 
 /*

diff --git a/kernel/fork.c b/kernel/fork.c
index cc760491f20127f44ab5db96ec7e858dcce77f54..3d590e51ce84dac4522718367191e09a5df0ea4e 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -832,7 +832,7 @@ static void check_mm(struct mm_struct *mm)
                pr_alert("BUG: non-zero pgtables_bytes on freeing mm: %ld\n",
                                mm_pgtables_bytes(mm));
 
-#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
+#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !defined(CONFIG_SPLIT_PMD_PTLOCKS)
        VM_BUG_ON_MM(mm->pmd_huge_pte, mm);
 #endif
 }
@@ -1276,7 +1276,7 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p,
        RCU_INIT_POINTER(mm->exe_file, NULL);
        mmu_notifier_subscriptions_init(mm);
        init_tlb_flush_pending(mm);
-#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
+#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !defined(CONFIG_SPLIT_PMD_PTLOCKS)
        mm->pmd_huge_pte = NULL;
 #endif
        mm_init_uprobes_state(mm);

diff --git a/mm/Kconfig b/mm/Kconfig
index b72e7d040f789fe14b8f598efd8cc493836b4269..7b716ac80272650d2d298ab1fd90cf9528a4750c 100644 (file)
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -585,17 +585,21 @@ config ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE
 # at the same time (e.g. copy_page_range()).
 # DEBUG_SPINLOCK and DEBUG_LOCK_ALLOC spinlock_t also enlarge struct page.
 #
-config SPLIT_PTLOCK_CPUS
-       int
-       default "999999" if !MMU
-       default "999999" if ARM && !CPU_CACHE_VIPT
-       default "999999" if PARISC && !PA20
-       default "999999" if SPARC32
-       default "4"
+config SPLIT_PTE_PTLOCKS
+       def_bool y
+       depends on MMU
+       depends on NR_CPUS >= 4
+       depends on !ARM || CPU_CACHE_VIPT
+       depends on !PARISC || PA20
+       depends on !SPARC32
 
 config ARCH_ENABLE_SPLIT_PMD_PTLOCK
        bool
 
+config SPLIT_PMD_PTLOCKS
+       def_bool y
+       depends on SPLIT_PTE_PTLOCKS && ARCH_ENABLE_SPLIT_PMD_PTLOCK
+
 #
 # support for memory balloon
 config MEMORY_BALLOON

diff --git a/mm/memory.c b/mm/memory.c
index a3d955098a192b97dd894903e71ac3aa0e278539..71236ae6fd144f04a2fd44fbb4545a65c0be424c 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -6571,7 +6571,7 @@ long copy_folio_from_user(struct folio *dst_folio,
 }
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS */
 
-#if USE_SPLIT_PTE_PTLOCKS && ALLOC_SPLIT_PTLOCKS
+#if defined(CONFIG_SPLIT_PTE_PTLOCKS) && ALLOC_SPLIT_PTLOCKS
 
 static struct kmem_cache *page_ptl_cachep;