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Kernel: Don't clone entire kernel stack on fork

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We only need to copy area between [ret_sp, stack_end]. This range is
always very small compared to the whole stack (64 KiB).
This commit is contained in:
Bananymous
2026-04-04 23:26:39 +03:00
parent 9d83424346
commit 9fce114e8e
3 changed files with 26 additions and 41 deletions
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35
kernel/kernel/Thread.cpp
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@@ -13,6 +13,12 @@
namespace Kernel
{
#if ARCH(x86_64)
static constexpr vaddr_t s_user_stack_addr_start = 0x0000700000000000;
#elif ARCH(i686)
static constexpr vaddr_t s_user_stack_addr_start = 0xB0000000;
#endif
extern "C" [[noreturn]] void start_kernel_thread();
extern "C" [[noreturn]] void start_userspace_thread();
@@ -200,15 +206,9 @@ namespace Kernel
thread->m_is_userspace = true;
#if ARCH(x86_64)
static constexpr vaddr_t stack_addr_start = 0x0000700000000000;
#elif ARCH(i686)
static constexpr vaddr_t stack_addr_start = 0xB0000000;
#endif
thread->m_kernel_stack = TRY(VirtualRange::create_to_vaddr_range(
page_table,
stack_addr_start, USERSPACE_END,
s_user_stack_addr_start, USERSPACE_END,
kernel_stack_size,
PageTable::Flags::ReadWrite | PageTable::Flags::Present,
true, true
@@ -217,7 +217,7 @@ namespace Kernel
auto userspace_stack = TRY(MemoryBackedRegion::create(
page_table,
userspace_stack_size,
{ stack_addr_start, USERSPACE_END },
{ s_user_stack_addr_start, USERSPACE_END },
MemoryRegion::Type::PRIVATE,
PageTable::Flags::UserSupervisor | PageTable::Flags::ReadWrite | PageTable::Flags::Present,
O_RDWR
@@ -346,7 +346,24 @@ namespace Kernel
thread->m_is_userspace = true;
thread->m_kernel_stack = TRY(m_kernel_stack->clone(new_process->page_table()));
thread->m_kernel_stack = TRY(VirtualRange::create_to_vaddr_range(
new_process->page_table(),
s_user_stack_addr_start, USERSPACE_END,
kernel_stack_size,
PageTable::Flags::ReadWrite | PageTable::Flags::Present,
true, true
));
// NOTE: copy [sp, stack_end] so fork return works
PageTable::with_fast_page(thread->m_kernel_stack->paddr_of(thread->kernel_stack_top() - PAGE_SIZE), [&] {
const size_t ncopy = kernel_stack_top() - sp;
ASSERT(ncopy <= PAGE_SIZE);
memcpy(
PageTable::fast_page_as_ptr(PAGE_SIZE - ncopy),
reinterpret_cast<void*>(sp),
ncopy
);
});
const auto stack_index = new_process->find_mapped_region(m_userspace_stack->vaddr());
thread->m_userspace_stack = static_cast<MemoryBackedRegion*>(new_process->m_mapped_regions[stack_index].ptr());