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Subject[RFC PATCH 15/26] hugetlb: make unmapping compatible with high-granularity mappings
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This enlightens __unmap_hugepage_range to deal with high-granularity
mappings. This doesn't change its API; it still must be called with
hugepage alignment, but it will correctly unmap hugepages that have been
mapped at high granularity.

Analogous to the mapcount rules introduced by hugetlb_no_page, we only
drop mapcount in this case if we are unmapping an entire hugepage in one
operation. This is the case when a VMA is destroyed.

Eventually, functionality here can be expanded to allow users to call
MADV_DONTNEED on PAGE_SIZE-aligned sections of a hugepage, but that is
not done here.

Signed-off-by: James Houghton <jthoughton@google.com>
---
include/asm-generic/tlb.h | 6 +--
mm/hugetlb.c | 85 ++++++++++++++++++++++++++-------------
2 files changed, 59 insertions(+), 32 deletions(-)

diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
index ff3e82553a76..8daa3ae460d9 100644
--- a/include/asm-generic/tlb.h
+++ b/include/asm-generic/tlb.h
@@ -562,9 +562,9 @@ static inline void tlb_flush_p4d_range(struct mmu_gather *tlb,
__tlb_remove_tlb_entry(tlb, ptep, address); \
} while (0)

-#define tlb_remove_huge_tlb_entry(h, tlb, ptep, address) \
+#define tlb_remove_huge_tlb_entry(tlb, hpte, address) \
do { \
- unsigned long _sz = huge_page_size(h); \
+ unsigned long _sz = hugetlb_pte_size(&hpte); \
if (_sz >= P4D_SIZE) \
tlb_flush_p4d_range(tlb, address, _sz); \
else if (_sz >= PUD_SIZE) \
@@ -573,7 +573,7 @@ static inline void tlb_flush_p4d_range(struct mmu_gather *tlb,
tlb_flush_pmd_range(tlb, address, _sz); \
else \
tlb_flush_pte_range(tlb, address, _sz); \
- __tlb_remove_tlb_entry(tlb, ptep, address); \
+ __tlb_remove_tlb_entry(tlb, hpte.ptep, address);\
} while (0)

/**
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index da30621656b8..51fc1d3f122f 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5120,24 +5120,20 @@ static void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct
{
struct mm_struct *mm = vma->vm_mm;
unsigned long address;
- pte_t *ptep;
+ struct hugetlb_pte hpte;
pte_t pte;
spinlock_t *ptl;
- struct page *page;
+ struct page *hpage, *subpage;
struct hstate *h = hstate_vma(vma);
unsigned long sz = huge_page_size(h);
struct mmu_notifier_range range;
bool force_flush = false;
+ bool hgm_enabled = hugetlb_hgm_enabled(vma);

WARN_ON(!is_vm_hugetlb_page(vma));
BUG_ON(start & ~huge_page_mask(h));
BUG_ON(end & ~huge_page_mask(h));

- /*
- * This is a hugetlb vma, all the pte entries should point
- * to huge page.
- */
- tlb_change_page_size(tlb, sz);
tlb_start_vma(tlb, vma);

/*
@@ -5148,25 +5144,43 @@ static void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct
adjust_range_if_pmd_sharing_possible(vma, &range.start, &range.end);
mmu_notifier_invalidate_range_start(&range);
address = start;
- for (; address < end; address += sz) {
- ptep = huge_pte_offset(mm, address, sz);
- if (!ptep)
+
+ while (address < end) {
+ pte_t *ptep = huge_pte_offset(mm, address, sz);
+
+ if (!ptep) {
+ address += sz;
continue;
+ }
+ hugetlb_pte_populate(&hpte, ptep, huge_page_shift(h));
+ if (hgm_enabled) {
+ int ret = huge_pte_alloc_high_granularity(
+ &hpte, mm, vma, address, PAGE_SHIFT,
+ HUGETLB_SPLIT_NEVER,
+ /*write_locked=*/true);
+ /*
+ * We will never split anything, so this should always
+ * succeed.
+ */
+ BUG_ON(ret);
+ }

- ptl = huge_pte_lock(h, mm, ptep);
- if (huge_pmd_unshare(mm, vma, &address, ptep)) {
+ ptl = hugetlb_pte_lock(mm, &hpte);
+ if (!hgm_enabled && huge_pmd_unshare(
+ mm, vma, &address, hpte.ptep)) {
spin_unlock(ptl);
tlb_flush_pmd_range(tlb, address & PUD_MASK, PUD_SIZE);
force_flush = true;
- continue;
+ goto next_hpte;
}

- pte = huge_ptep_get(ptep);
- if (huge_pte_none(pte)) {
+ if (hugetlb_pte_none(&hpte)) {
spin_unlock(ptl);
- continue;
+ goto next_hpte;
}

+ pte = hugetlb_ptep_get(&hpte);
+
/*
* Migrating hugepage or HWPoisoned hugepage is already
* unmapped and its refcount is dropped, so just clear pte here.
@@ -5180,24 +5194,27 @@ static void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct
*/
if (pte_swp_uffd_wp_any(pte) &&
!(zap_flags & ZAP_FLAG_DROP_MARKER))
- set_huge_pte_at(mm, address, ptep,
+ set_huge_pte_at(mm, address, hpte.ptep,
make_pte_marker(PTE_MARKER_UFFD_WP));
else
- huge_pte_clear(mm, address, ptep, sz);
+ huge_pte_clear(mm, address, hpte.ptep,
+ hugetlb_pte_size(&hpte));
spin_unlock(ptl);
- continue;
+ goto next_hpte;
}

- page = pte_page(pte);
+ subpage = pte_page(pte);
+ BUG_ON(!subpage);
+ hpage = compound_head(subpage);
/*
* If a reference page is supplied, it is because a specific
* page is being unmapped, not a range. Ensure the page we
* are about to unmap is the actual page of interest.
*/
if (ref_page) {
- if (page != ref_page) {
+ if (hpage != ref_page) {
spin_unlock(ptl);
- continue;
+ goto next_hpte;
}
/*
* Mark the VMA as having unmapped its page so that
@@ -5207,25 +5224,35 @@ static void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct
set_vma_resv_flags(vma, HPAGE_RESV_UNMAPPED);
}

- pte = huge_ptep_get_and_clear(mm, address, ptep);
- tlb_remove_huge_tlb_entry(h, tlb, ptep, address);
+ pte = huge_ptep_get_and_clear(mm, address, hpte.ptep);
+ tlb_change_page_size(tlb, hugetlb_pte_size(&hpte));
+ tlb_remove_huge_tlb_entry(tlb, hpte, address);
if (huge_pte_dirty(pte))
- set_page_dirty(page);
+ set_page_dirty(hpage);
/* Leave a uffd-wp pte marker if needed */
if (huge_pte_uffd_wp(pte) &&
!(zap_flags & ZAP_FLAG_DROP_MARKER))
- set_huge_pte_at(mm, address, ptep,
+ set_huge_pte_at(mm, address, hpte.ptep,
make_pte_marker(PTE_MARKER_UFFD_WP));
- hugetlb_count_sub(pages_per_huge_page(h), mm);
- page_remove_rmap(page, vma, true);
+
+ hugetlb_count_sub(hugetlb_pte_size(&hpte)/PAGE_SIZE, mm);
+
+ /*
+ * If we are unmapping the entire page, remove it from the
+ * rmap.
+ */
+ if (IS_ALIGNED(address, sz) && address + sz <= end)
+ page_remove_rmap(hpage, vma, true);

spin_unlock(ptl);
- tlb_remove_page_size(tlb, page, huge_page_size(h));
+ tlb_remove_page_size(tlb, subpage, hugetlb_pte_size(&hpte));
/*
* Bail out after unmapping reference page if supplied
*/
if (ref_page)
break;
+next_hpte:
+ address += hugetlb_pte_size(&hpte);
}
mmu_notifier_invalidate_range_end(&range);
tlb_end_vma(tlb, vma);
--
2.37.0.rc0.161.g10f37bed90-goog
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