Date:   Wed, 15 Feb 2023 21:17:35 -0800
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Subject: [PATCH v3 20/35] mm: conditionally write-lock VMA in free_pgtables
From:   Suren Baghdasaryan <surenb@google.com>
To:     akpm@linux-foundation.org
Cc:     michel@lespinasse.org, jglisse@google.com, mhocko@suse.com,
        vbabka@suse.cz, hannes@cmpxchg.org, mgorman@techsingularity.net,
        dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com,
        peterz@infradead.org, ldufour@linux.ibm.com, paulmck@kernel.org,
        mingo@redhat.com, will@kernel.org, luto@kernel.org,
        songliubraving@fb.com, peterx@redhat.com, david@redhat.com,
        dhowells@redhat.com, hughd@google.com, bigeasy@linutronix.de,
        kent.overstreet@linux.dev, punit.agrawal@bytedance.com,
        lstoakes@gmail.com, peterjung1337@gmail.com, rientjes@google.com,
        chriscli@google.com, axelrasmussen@google.com, joelaf@google.com,
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        gthelen@google.com, gurua@google.com, arjunroy@google.com,
        soheil@google.com, leewalsh@google.com, posk@google.com,
        michalechner92@googlemail.com, linux-mm@kvack.org,
        linux-arm-kernel@lists.infradead.org,
        linuxppc-dev@lists.ozlabs.org, x86@kernel.org,
        linux-kernel@vger.kernel.org, kernel-team@android.com,
        Suren Baghdasaryan <surenb@google.com>
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Normally free_pgtables needs to lock affected VMAs except for the case
when VMAs were isolated under VMA write-lock. munmap() does just that,
isolating while holding appropriate locks and then downgrading mmap_lock
and dropping per-VMA locks before freeing page tables.
Add a parameter to free_pgtables for such scenario.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 mm/internal.h | 2 +-
 mm/memory.c   | 6 +++++-
 mm/mmap.c     | 5 +++--
 3 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/mm/internal.h b/mm/internal.h
index fc01fd092ea5..400c302fbf47 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -105,7 +105,7 @@ void folio_activate(struct folio *folio);
 
 void free_pgtables(struct mmu_gather *tlb, struct maple_tree *mt,
 		   struct vm_area_struct *start_vma, unsigned long floor,
-		   unsigned long ceiling);
+		   unsigned long ceiling, bool mm_wr_locked);
 void pmd_install(struct mm_struct *mm, pmd_t *pmd, pgtable_t *pte);
 
 struct zap_details;
diff --git a/mm/memory.c b/mm/memory.c
index f456f3b5049c..8177c59ffd2d 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -348,7 +348,7 @@ void free_pgd_range(struct mmu_gather *tlb,
 
 void free_pgtables(struct mmu_gather *tlb, struct maple_tree *mt,
 		   struct vm_area_struct *vma, unsigned long floor,
-		   unsigned long ceiling)
+		   unsigned long ceiling, bool mm_wr_locked)
 {
 	MA_STATE(mas, mt, vma->vm_end, vma->vm_end);
 
@@ -366,6 +366,8 @@ void free_pgtables(struct mmu_gather *tlb, struct maple_tree *mt,
 		 * Hide vma from rmap and truncate_pagecache before freeing
 		 * pgtables
 		 */
+		if (mm_wr_locked)
+			vma_start_write(vma);
 		unlink_anon_vmas(vma);
 		unlink_file_vma(vma);
 
@@ -380,6 +382,8 @@ void free_pgtables(struct mmu_gather *tlb, struct maple_tree *mt,
 			       && !is_vm_hugetlb_page(next)) {
 				vma = next;
 				next = mas_find(&mas, ceiling - 1);
+				if (mm_wr_locked)
+					vma_start_write(vma);
 				unlink_anon_vmas(vma);
 				unlink_file_vma(vma);
 			}
diff --git a/mm/mmap.c b/mm/mmap.c
index aaa359a147b2..118b2246bba9 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2157,7 +2157,8 @@ static void unmap_region(struct mm_struct *mm, struct maple_tree *mt,
 	update_hiwater_rss(mm);
 	unmap_vmas(&tlb, mt, vma, start, end, mm_wr_locked);
 	free_pgtables(&tlb, mt, vma, prev ? prev->vm_end : FIRST_USER_ADDRESS,
-				 next ? next->vm_start : USER_PGTABLES_CEILING);
+				 next ? next->vm_start : USER_PGTABLES_CEILING,
+				 mm_wr_locked);
 	tlb_finish_mmu(&tlb);
 }
 
@@ -3069,7 +3070,7 @@ void exit_mmap(struct mm_struct *mm)
 	mmap_write_lock(mm);
 	mt_clear_in_rcu(&mm->mm_mt);
 	free_pgtables(&tlb, &mm->mm_mt, vma, FIRST_USER_ADDRESS,
-		      USER_PGTABLES_CEILING);
+		      USER_PGTABLES_CEILING, true);
 	tlb_finish_mmu(&tlb);
 
 	/*
-- 
2.39.1