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Kernel: Use RAII to manage committed physical pages

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We had issues with committed physical pages getting miscounted in some
situations, and instead of figuring out what was going wrong and making
sure all the commits had matching uncommits, this patch makes the
problem go away by adding an RAII class to manage this instead. :^)

MemoryManager::commit_user_physical_pages() now returns an (optional)
CommittedPhysicalPageSet. You can then allocate pages from the page set
by calling take_one() on it. Any unallocated pages are uncommitted upon
destruction of the page set.
This commit is contained in:
Andreas Kling 2021-08-04 22:49:13 +02:00
parent ec49213f7b
commit fa627c1eb2
4 changed files with 121 additions and 93 deletions
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29
Kernel/VM/MemoryManager.cpp
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@ -69,10 +69,9 @@ UNMAP_AFTER_INIT MemoryManager::MemoryManager()
protect_kernel_image();
// We're temporarily "committing" to two pages that we need to allocate below
if (!commit_user_physical_pages(2))
VERIFY_NOT_REACHED();
auto committed_pages = commit_user_physical_pages(2);
m_shared_zero_page = allocate_committed_user_physical_page();
m_shared_zero_page = committed_pages->take_one();
// We're wasting a page here, we just need a special tag (physical
// address) so that we know when we need to lazily allocate a page
@ -80,7 +79,7 @@ UNMAP_AFTER_INIT MemoryManager::MemoryManager()
// than potentially failing if no pages are available anymore.
// By using a tag we don't have to query the VMObject for every page
// whether it was committed or not
m_lazy_committed_page = allocate_committed_user_physical_page();
m_lazy_committed_page = committed_pages->take_one();
}
UNMAP_AFTER_INIT MemoryManager::~MemoryManager()
@ -766,21 +765,22 @@ OwnPtr<Region> MemoryManager::allocate_kernel_region_with_vmobject(VMObject& vmo
return allocate_kernel_region_with_vmobject(range.value(), vmobject, name, access, cacheable);
}
bool MemoryManager::commit_user_physical_pages(size_t page_count)
Optional<CommittedPhysicalPageSet> MemoryManager::commit_user_physical_pages(size_t page_count)
{
VERIFY(page_count > 0);
ScopedSpinLock lock(s_mm_lock);
if (m_system_memory_info.user_physical_pages_uncommitted < page_count)
return false;
return {};
m_system_memory_info.user_physical_pages_uncommitted -= page_count;
m_system_memory_info.user_physical_pages_committed += page_count;
return true;
return CommittedPhysicalPageSet { {}, page_count };
}
void MemoryManager::uncommit_user_physical_pages(size_t page_count)
void MemoryManager::uncommit_user_physical_pages(Badge<CommittedPhysicalPageSet>, size_t page_count)
{
VERIFY(page_count > 0);
ScopedSpinLock lock(s_mm_lock);
VERIFY(m_system_memory_info.user_physical_pages_committed >= page_count);
@ -1124,4 +1124,17 @@ void MemoryManager::set_page_writable_direct(VirtualAddress vaddr, bool writable
flush_tlb(&kernel_page_directory(), vaddr);
}
CommittedPhysicalPageSet::~CommittedPhysicalPageSet()
{
if (m_page_count)
MM.uncommit_user_physical_pages({}, m_page_count);
}
NonnullRefPtr<PhysicalPage> CommittedPhysicalPageSet::take_one()
{
VERIFY(m_page_count > 0);
--m_page_count;
return MM.allocate_committed_user_physical_page(MemoryManager::ShouldZeroFill::Yes);
}
}