Remove CppgcBoundedPageAllocator

This allocator was only required to ensure zero-initialization of pages
returned by the BoundedPageAllocator. With crrev/c/3208812, this is now
possible in a (hopefully) more efficient way by using the
kAllocatedPagesMustBeZeroInitialized PageInitializationMode.

Bug: chromium:1218005
Change-Id: I504248107a54c90285aa9a3a616b334aaa3fcb7a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3211583Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Samuel Groß <saelo@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77298}

src/base/sanitizer/lsan-page-allocator.h

@@ -49,6 +49,10 @@ class V8_BASE_EXPORT LsanPageAllocator : public v8::PageAllocator {
     return page_allocator_->SetPermissions(address, size, access);
   }
 
+  bool DecommitPages(void* address, size_t size) override {
+    return page_allocator_->DecommitPages(address, size);
+  }
+
  private:
   v8::PageAllocator* const page_allocator_;
   const size_t allocate_page_size_;

src/heap/cppgc/caged-heap.cc

@@ -46,29 +46,6 @@ VirtualMemory ReserveCagedHeap(PageAllocator& platform_allocator) {
   UNREACHABLE();
 }
 
-class CppgcBoundedPageAllocator final : public v8::base::BoundedPageAllocator {
- public:
-  CppgcBoundedPageAllocator(v8::PageAllocator* page_allocator, Address start,
-                            size_t size, size_t allocate_page_size)
-      : BoundedPageAllocator(page_allocator, start, size, allocate_page_size,
-                             v8::base::PageInitializationMode::
-                                 kAllocatedPagesCanBeUninitialized) {}
-
-  bool FreePages(void* address, size_t size) final {
-    // BoundedPageAllocator is not guaranteed to allocate zeroed page.
-    // Specifically it is possible that BPA frees a page and then tries to
-    // reallocate the same page before the OS has had a chance to asyncroniously
-    // reclaim that page. In such cases, the contents of the page would not have
-    // been cleared by the OS and the reallocated page will keep its previous
-    // contents. To mitigate this problem, CppgcBoundedPageAllocator clears all
-    // pages before they are freed. This also includes protected guard pages, so
-    // CppgcBoundedPageAllocator needs to update permissions before clearing.
-    CHECK(SetPermissions(address, size, Permission::kReadWrite));
-    memset(address, 0, size);
-    return v8::base::BoundedPageAllocator::FreePages(address, size);
-  }
-};
-
 }  // namespace
 
 CagedHeap::CagedHeap(HeapBase& heap_base, PageAllocator& platform_allocator)
@@ -93,9 +70,10 @@ CagedHeap::CagedHeap(HeapBase& heap_base, PageAllocator& platform_allocator)
       caged_heap_start -
       reinterpret_cast<CagedAddress>(reserved_area_.address());
 
-  bounded_allocator_ = std::make_unique<CppgcBoundedPageAllocator>(
+  bounded_allocator_ = std::make_unique<v8::base::BoundedPageAllocator>(
       &platform_allocator, caged_heap_start,
-      reserved_area_.size() - local_data_size_with_padding, kPageSize);
+      reserved_area_.size() - local_data_size_with_padding, kPageSize,
+      v8::base::PageInitializationMode::kAllocatedPagesMustBeZeroInitialized);
 }
 
 }  // namespace internal