+ mm-turn-use_split_pte_ptlocks-use_split_pte_ptlocks-into-kconfig-options.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm: turn USE_SPLIT_PTE_PTLOCKS / USE_SPLIT_PTE_PTLOCKS into Kconfig options
has been added to the -mm mm-unstable branch.  Its filename is
     mm-turn-use_split_pte_ptlocks-use_split_pte_ptlocks-into-kconfig-options.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-turn-use_split_pte_ptlocks-use_split_pte_ptlocks-into-kconfig-options.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: David Hildenbrand <david@redhat.com>
Subject: mm: turn USE_SPLIT_PTE_PTLOCKS / USE_SPLIT_PTE_PTLOCKS into Kconfig options
Date: Fri, 26 Jul 2024 17:07:26 +0200

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>
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: Russell King <linux@armlinux.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 arch/arm/mm/fault-armv.c      |    6 +++---
 arch/x86/xen/mmu_pv.c         |    7 ++++---
 include/linux/mm.h            |    8 ++++----
 include/linux/mm_types.h      |    2 +-
 include/linux/mm_types_task.h |    3 ---
 kernel/fork.c                 |    4 ++--
 mm/Kconfig                    |   18 +++++++++++-------
 mm/memory.c                   |    2 +-
 8 files changed, 26 insertions(+), 24 deletions(-)

--- a/arch/arm/mm/fault-armv.c~mm-turn-use_split_pte_ptlocks-use_split_pte_ptlocks-into-kconfig-options
+++ a/arch/arm/mm/fault-armv.c
@@ -61,7 +61,7 @@ static int do_adjust_pte(struct vm_area_
 	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(spinloc
 {
 	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)
--- a/arch/x86/xen/mmu_pv.c~mm-turn-use_split_pte_ptlocks-use_split_pte_ptlocks-into-kconfig-options
+++ a/arch/x86/xen/mmu_pv.c
@@ -665,7 +665,7 @@ static spinlock_t *xen_pte_lock(struct p
 {
 	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(stru
 
 		__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(un
 	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);
--- a/include/linux/mm.h~mm-turn-use_split_pte_ptlocks-use_split_pte_ptlocks-into-kconfig-options
+++ a/include/linux/mm.h
@@ -2891,7 +2891,7 @@ static inline void pagetable_free(struct
 	__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);
@@ -2943,7 +2943,7 @@ static inline bool ptlock_init(struct pt
 	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.
  */
@@ -2954,7 +2954,7 @@ static inline spinlock_t *pte_lockptr(st
 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)
 {
@@ -3014,7 +3014,7 @@ pte_t *pte_offset_map_nolock(struct mm_s
 	((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)
 {
--- a/include/linux/mm_types.h~mm-turn-use_split_pte_ptlocks-use_split_pte_ptlocks-into-kconfig-options
+++ a/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
--- a/include/linux/mm_types_task.h~mm-turn-use_split_pte_ptlocks-use_split_pte_ptlocks-into-kconfig-options
+++ a/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)
 
 /*
--- a/kernel/fork.c~mm-turn-use_split_pte_ptlocks-use_split_pte_ptlocks-into-kconfig-options
+++ a/kernel/fork.c
@@ -832,7 +832,7 @@ static void check_mm(struct mm_struct *m
 		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
 	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);
--- a/mm/Kconfig~mm-turn-use_split_pte_ptlocks-use_split_pte_ptlocks-into-kconfig-options
+++ a/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
--- a/mm/memory.c~mm-turn-use_split_pte_ptlocks-use_split_pte_ptlocks-into-kconfig-options
+++ a/mm/memory.c
@@ -6572,7 +6572,7 @@ long copy_folio_from_user(struct 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;
 
_

Patches currently in -mm which might be from david@redhat.com are

mm-let-pte_lockptr-consume-a-pte_t-pointer.patch
mm-hugetlb-fix-hugetlb-vs-core-mm-pt-locking.patch
mm-turn-use_split_pte_ptlocks-use_split_pte_ptlocks-into-kconfig-options.patch
mm-hugetlb-enforce-that-pmd-pt-sharing-has-split-pmd-pt-locks.patch
powerpc-8xx-document-and-enforce-that-split-pt-locks-are-not-used.patch