linux-kernel - [PATCH 16/41] mm: replace vma->vm_flags indirect modification in ksm

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Date:   Mon,  9 Jan 2023 12:53:11 -0800
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     akpm@...ux-foundation.org
Cc:     michel@...pinasse.org, jglisse@...gle.com, mhocko@...e.com,
        vbabka@...e.cz, hannes@...xchg.org, mgorman@...hsingularity.net,
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        peterz@...radead.org, ldufour@...ux.ibm.com,
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        surenb@...gle.com
Subject: [PATCH 16/41] mm: replace vma->vm_flags indirect modification in ksm_madvise

Replace indirect modifications to vma->vm_flags with calls to modifier
functions to be able to track flag changes and to keep vma locking
correctness. Add a BUG_ON check in ksm_madvise() to catch indirect
vm_flags modification attempts.

Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
---
 arch/powerpc/kvm/book3s_hv_uvmem.c | 5 ++++-
 arch/s390/mm/gmap.c                | 5 ++++-
 mm/khugepaged.c                    | 2 ++
 mm/ksm.c                           | 2 ++
 4 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c
index 1d67baa5557a..325a7a47d348 100644
--- a/arch/powerpc/kvm/book3s_hv_uvmem.c
+++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
@@ -393,6 +393,7 @@ static int kvmppc_memslot_page_merge(struct kvm *kvm,
 {
 	unsigned long gfn = memslot->base_gfn;
 	unsigned long end, start = gfn_to_hva(kvm, gfn);
+	unsigned long vm_flags;
 	int ret = 0;
 	struct vm_area_struct *vma;
 	int merge_flag = (merge) ? MADV_MERGEABLE : MADV_UNMERGEABLE;
@@ -409,12 +410,14 @@ static int kvmppc_memslot_page_merge(struct kvm *kvm,
 			ret = H_STATE;
 			break;
 		}
+		vm_flags = vma->vm_flags;
 		ret = ksm_madvise(vma, vma->vm_start, vma->vm_end,
-			  merge_flag, &vma->vm_flags);
+			  merge_flag, &vm_flags);
 		if (ret) {
 			ret = H_STATE;
 			break;
 		}
+		reset_vm_flags(vma, vm_flags);
 		start = vma->vm_end;
 	} while (end > vma->vm_end);
 
diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
index 3811d6c86d09..e47387f8be6d 100644
--- a/arch/s390/mm/gmap.c
+++ b/arch/s390/mm/gmap.c
@@ -2587,14 +2587,17 @@ int gmap_mark_unmergeable(void)
 {
 	struct mm_struct *mm = current->mm;
 	struct vm_area_struct *vma;
+	unsigned long vm_flags;
 	int ret;
 	VMA_ITERATOR(vmi, mm, 0);
 
 	for_each_vma(vmi, vma) {
+		vm_flags = vma->vm_flags;
 		ret = ksm_madvise(vma, vma->vm_start, vma->vm_end,
-				  MADV_UNMERGEABLE, &vma->vm_flags);
+				  MADV_UNMERGEABLE, &vm_flags);
 		if (ret)
 			return ret;
+		reset_vm_flags(vma, vm_flags);
 	}
 	mm->def_flags &= ~VM_MERGEABLE;
 	return 0;
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 5cb401aa2b9d..5376246a3052 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -352,6 +352,8 @@ struct attribute_group khugepaged_attr_group = {
 int hugepage_madvise(struct vm_area_struct *vma,
 		     unsigned long *vm_flags, int advice)
 {
+	/* vma->vm_flags can be changed only using modifier functions */
+	BUG_ON(vm_flags == &vma->vm_flags);
 	switch (advice) {
 	case MADV_HUGEPAGE:
 #ifdef CONFIG_S390
diff --git a/mm/ksm.c b/mm/ksm.c
index dd02780c387f..d05c41b289db 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -2471,6 +2471,8 @@ int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
 	struct mm_struct *mm = vma->vm_mm;
 	int err;
 
+	/* vma->vm_flags can be changed only using modifier functions */
+	BUG_ON(vm_flags == &vma->vm_flags);
 	switch (advice) {
 	case MADV_MERGEABLE:
 		/*
-- 
2.39.0