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50472fd69f
When we get a COW fault and discover that whoever we were COW'ing together with has either COW'ed that page on their end (or they have unmapped/exited) we simplify life for ourselves by clearing the COW bit and keeping the page we already have. (No need to COW if the page is not shared!) The act of doing this does not return a committed page to the pool. In fact, that committed page we had reserved for this purpose was used up (allocated) by our COW buddy when they COW'ed the page. This fixes a kernel panic when running TestLibCMkTemp. :^)
85 lines
2.7 KiB
C++
85 lines
2.7 KiB
C++
/*
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* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include <Kernel/PhysicalAddress.h>
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#include <Kernel/VM/AllocationStrategy.h>
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#include <Kernel/VM/MemoryManager.h>
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#include <Kernel/VM/PageFaultResponse.h>
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#include <Kernel/VM/VMObject.h>
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namespace Kernel {
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class CommittedCowPages : public RefCounted<CommittedCowPages> {
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AK_MAKE_NONCOPYABLE(CommittedCowPages);
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public:
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CommittedCowPages() = delete;
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explicit CommittedCowPages(size_t);
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~CommittedCowPages();
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[[nodiscard]] NonnullRefPtr<PhysicalPage> allocate_one();
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[[nodiscard]] size_t is_empty() const { return m_committed_pages == 0; }
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public:
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size_t m_committed_pages { 0 };
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};
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class AnonymousVMObject final : public VMObject {
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public:
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virtual ~AnonymousVMObject() override;
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static RefPtr<AnonymousVMObject> try_create_with_size(size_t, AllocationStrategy);
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static RefPtr<AnonymousVMObject> try_create_for_physical_range(PhysicalAddress paddr, size_t size);
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static RefPtr<AnonymousVMObject> try_create_with_physical_pages(Span<NonnullRefPtr<PhysicalPage>>);
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static RefPtr<AnonymousVMObject> try_create_purgeable_with_size(size_t, AllocationStrategy);
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static RefPtr<AnonymousVMObject> try_create_physically_contiguous_with_size(size_t);
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virtual RefPtr<VMObject> try_clone() override;
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[[nodiscard]] NonnullRefPtr<PhysicalPage> allocate_committed_page(Badge<Region>);
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PageFaultResponse handle_cow_fault(size_t, VirtualAddress);
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size_t cow_pages() const;
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bool should_cow(size_t page_index, bool) const;
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void set_should_cow(size_t page_index, bool);
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bool is_purgeable() const { return m_purgeable; }
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bool is_volatile() const { return m_volatile; }
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KResult set_volatile(bool is_volatile, bool& was_purged);
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size_t purge();
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private:
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explicit AnonymousVMObject(size_t, AllocationStrategy);
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explicit AnonymousVMObject(PhysicalAddress, size_t);
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explicit AnonymousVMObject(Span<NonnullRefPtr<PhysicalPage>>);
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explicit AnonymousVMObject(AnonymousVMObject const&);
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virtual StringView class_name() const override { return "AnonymousVMObject"sv; }
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AnonymousVMObject& operator=(AnonymousVMObject const&) = delete;
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AnonymousVMObject& operator=(AnonymousVMObject&&) = delete;
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AnonymousVMObject(AnonymousVMObject&&) = delete;
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virtual bool is_anonymous() const override { return true; }
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Bitmap& ensure_cow_map();
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void ensure_or_reset_cow_map();
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size_t m_unused_committed_pages { 0 };
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Bitmap m_cow_map;
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// We share a pool of committed cow-pages with clones
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RefPtr<CommittedCowPages> m_shared_committed_cow_pages;
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bool m_purgeable { false };
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bool m_volatile { false };
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bool m_was_purged { false };
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};
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}
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