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Date:   Thu,  5 Jan 2023 10:18:05 +0000
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Message-ID: <20230105101844.1893104-8-jthoughton@google.com>
Subject: [PATCH 07/46] hugetlb: rename __vma_shareable_flags_pmd to __vma_has_hugetlb_vma_lock
From:   James Houghton <jthoughton@google.com>
To:     Mike Kravetz <mike.kravetz@oracle.com>,
        Muchun Song <songmuchun@bytedance.com>,
        Peter Xu <peterx@redhat.com>
Cc:     David Hildenbrand <david@redhat.com>,
        David Rientjes <rientjes@google.com>,
        Axel Rasmussen <axelrasmussen@google.com>,
        Mina Almasry <almasrymina@google.com>,
        "Zach O'Keefe" <zokeefe@google.com>,
        Manish Mishra <manish.mishra@nutanix.com>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>,
        "Dr . David Alan Gilbert" <dgilbert@redhat.com>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Baolin Wang <baolin.wang@linux.alibaba.com>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Yang Shi <shy828301@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        James Houghton <jthoughton@google.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Previously, if the hugetlb VMA lock was present, that meant that the VMA
was PMD-shareable. Now it is possible that the VMA lock is allocated but
the VMA is not PMD-shareable: if the VMA is a high-granularity VMA.

It is possible for a high-granularity VMA not to have a VMA lock; in
this case, MADV_COLLAPSE will not be able to collapse the mappings.

Signed-off-by: James Houghton <jthoughton@google.com>
---
 include/linux/hugetlb.h | 15 ++++++++++-----
 mm/hugetlb.c            | 16 ++++++++--------
 2 files changed, 18 insertions(+), 13 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index b6b10101bea7..aa49fd8cb47c 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -1235,7 +1235,8 @@ bool want_pmd_share(struct vm_area_struct *vma, unsigned long addr);
 #define flush_hugetlb_tlb_range(vma, addr, end)	flush_tlb_range(vma, addr, end)
 #endif
 
-static inline bool __vma_shareable_lock(struct vm_area_struct *vma)
+static inline bool
+__vma_has_hugetlb_vma_lock(struct vm_area_struct *vma)
 {
 	return (vma->vm_flags & VM_MAYSHARE) && vma->vm_private_data;
 }
@@ -1252,13 +1253,17 @@ hugetlb_walk(struct vm_area_struct *vma, unsigned long addr, unsigned long sz)
 	struct hugetlb_vma_lock *vma_lock = vma->vm_private_data;
 
 	/*
-	 * If pmd sharing possible, locking needed to safely walk the
-	 * hugetlb pgtables.  More information can be found at the comment
-	 * above huge_pte_offset() in the same file.
+	 * If the VMA has the hugetlb vma lock (PMD sharable or HGM
+	 * collapsible), locking needed to safely walk the hugetlb pgtables.
+	 * More information can be found at the comment above huge_pte_offset()
+	 * in the same file.
+	 *
+	 * This doesn't do a full high-granularity walk, so we are concerned
+	 * only with PMD unsharing.
 	 *
 	 * NOTE: lockdep_is_held() is only defined with CONFIG_LOCKDEP.
 	 */
-	if (__vma_shareable_lock(vma))
+	if (__vma_has_hugetlb_vma_lock(vma))
 		WARN_ON_ONCE(!lockdep_is_held(&vma_lock->rw_sema) &&
 			     !lockdep_is_held(
 				 &vma->vm_file->f_mapping->i_mmap_rwsem));
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 99fadd7680ec..2f86fedef283 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -260,7 +260,7 @@ static inline struct hugepage_subpool *subpool_vma(struct vm_area_struct *vma)
  */
 void hugetlb_vma_lock_read(struct vm_area_struct *vma)
 {
-	if (__vma_shareable_lock(vma)) {
+	if (__vma_has_hugetlb_vma_lock(vma)) {
 		struct hugetlb_vma_lock *vma_lock = vma->vm_private_data;
 
 		down_read(&vma_lock->rw_sema);
@@ -269,7 +269,7 @@ void hugetlb_vma_lock_read(struct vm_area_struct *vma)
 
 void hugetlb_vma_unlock_read(struct vm_area_struct *vma)
 {
-	if (__vma_shareable_lock(vma)) {
+	if (__vma_has_hugetlb_vma_lock(vma)) {
 		struct hugetlb_vma_lock *vma_lock = vma->vm_private_data;
 
 		up_read(&vma_lock->rw_sema);
@@ -278,7 +278,7 @@ void hugetlb_vma_unlock_read(struct vm_area_struct *vma)
 
 void hugetlb_vma_lock_write(struct vm_area_struct *vma)
 {
-	if (__vma_shareable_lock(vma)) {
+	if (__vma_has_hugetlb_vma_lock(vma)) {
 		struct hugetlb_vma_lock *vma_lock = vma->vm_private_data;
 
 		down_write(&vma_lock->rw_sema);
@@ -287,7 +287,7 @@ void hugetlb_vma_lock_write(struct vm_area_struct *vma)
 
 void hugetlb_vma_unlock_write(struct vm_area_struct *vma)
 {
-	if (__vma_shareable_lock(vma)) {
+	if (__vma_has_hugetlb_vma_lock(vma)) {
 		struct hugetlb_vma_lock *vma_lock = vma->vm_private_data;
 
 		up_write(&vma_lock->rw_sema);
@@ -298,7 +298,7 @@ int hugetlb_vma_trylock_write(struct vm_area_struct *vma)
 {
 	struct hugetlb_vma_lock *vma_lock = vma->vm_private_data;
 
-	if (!__vma_shareable_lock(vma))
+	if (!__vma_has_hugetlb_vma_lock(vma))
 		return 1;
 
 	return down_write_trylock(&vma_lock->rw_sema);
@@ -306,7 +306,7 @@ int hugetlb_vma_trylock_write(struct vm_area_struct *vma)
 
 void hugetlb_vma_assert_locked(struct vm_area_struct *vma)
 {
-	if (__vma_shareable_lock(vma)) {
+	if (__vma_has_hugetlb_vma_lock(vma)) {
 		struct hugetlb_vma_lock *vma_lock = vma->vm_private_data;
 
 		lockdep_assert_held(&vma_lock->rw_sema);
@@ -338,7 +338,7 @@ static void __hugetlb_vma_unlock_write_put(struct hugetlb_vma_lock *vma_lock)
 
 static void __hugetlb_vma_unlock_write_free(struct vm_area_struct *vma)
 {
-	if (__vma_shareable_lock(vma)) {
+	if (__vma_has_hugetlb_vma_lock(vma)) {
 		struct hugetlb_vma_lock *vma_lock = vma->vm_private_data;
 
 		__hugetlb_vma_unlock_write_put(vma_lock);
@@ -350,7 +350,7 @@ static void hugetlb_vma_lock_free(struct vm_area_struct *vma)
 	/*
 	 * Only present in sharable vmas.
 	 */
-	if (!vma || !__vma_shareable_lock(vma))
+	if (!vma || !__vma_has_hugetlb_vma_lock(vma))
 		return;
 
 	if (vma->vm_private_data) {
-- 
2.39.0.314.g84b9a713c41-goog