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Kernel: Allow zero-fill page faults on kernel-only pages

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We were short-circuiting the page fault handler a little too eagerly
for page-not-present faults in kernel memory.
If the current page directory already has up-to-date mapps for kernel
memory, allow it to progress to checking for zero-fill conditions.

This will enable us to have lazily populated kernel regions.
This commit is contained in:
Andreas Kling 2019-08-06 14:01:29 +02:00
parent da615e46cd
commit a0bb592b4f
Notes: sideshowbarker 2024-07-19 12:51:11 +09:00
1 changed files with 6 additions and 4 deletions
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10
Kernel/VM/MemoryManager.cpp
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@ -416,12 +416,14 @@ PageFaultResponse MemoryManager::handle_page_fault(const PageFault& fault)
#endif
ASSERT(fault.vaddr() != m_quickmap_addr);
if (fault.type() == PageFault::Type::PageNotPresent && fault.vaddr().get() >= 0xc0000000) {
auto* current_page_directory = reinterpret_cast<PageDirectoryEntry*>(cpu_cr3());
u32 page_directory_index = (fault.vaddr().get() >> 22) & 0x3ff;
auto& kernel_pde = kernel_page_directory().entries()[page_directory_index];
if (kernel_pde.is_present()) {
dbgprintf("NP(kernel): copying new kernel mapping for L%x into current page directory\n", fault.vaddr().get());
auto* current_page_directory = reinterpret_cast<PageDirectoryEntry*>(cpu_cr3());
current_page_directory[page_directory_index].copy_from({}, kernel_pde);
auto& current_pde = current_page_directory[page_directory_index];
if (kernel_pde.is_present() && !current_pde.is_present()) {
dbg() << "NP(kernel): Copying new kernel mapping for " << fault.vaddr() << " into current page directory";
current_pde.copy_from({}, kernel_pde);
flush_tlb(fault.vaddr().page_base());
return PageFaultResponse::Continue;
}