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Kernel: Implement a simple virtual address range allocator.

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This replaces the previous virtual address allocator which was basically
just "m_next_address += size;"

With this in place, virtual addresses can get reused, which cuts down on
the number of page tables created. When we implement ASLR some day, we'll
probably have to do page table deallocation, but for now page tables are
only deallocated once the process dies.
This commit is contained in:
Andreas Kling 2019-05-17 03:40:15 +02:00
parent c56e3ebee1
commit c414e65498
5 changed files with 231 additions and 22 deletions
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53
Kernel/Process.cpp
View file

@ -70,14 +70,16 @@ bool Process::in_group(gid_t gid) const
Region* Process::allocate_region(LinearAddress laddr, size_t size, String&& name, bool is_readable, bool is_writable, bool commit)
{
laddr.mask(PAGE_MASK);
size = PAGE_ROUND_UP(size);
// FIXME: This needs sanity checks. What if this overlaps existing regions?
if (laddr.is_null()) {
laddr = m_next_region;
m_next_region = m_next_region.offset(size).offset(PAGE_SIZE);
}
laddr.mask(0xfffff000);
m_regions.append(adopt(*new Region(laddr, size, move(name), is_readable, is_writable)));
Range range;
if (laddr.is_null())
range = m_range_allocator.allocate_anywhere(size);
else
range = m_range_allocator.allocate_specific(laddr, size);
m_regions.append(adopt(*new Region(range.base(), range.size(), move(name), is_readable, is_writable)));
MM.map_region(*this, *m_regions.last());
if (commit)
m_regions.last()->commit();
@ -86,30 +88,34 @@ Region* Process::allocate_region(LinearAddress laddr, size_t size, String&& name
Region* Process::allocate_file_backed_region(LinearAddress laddr, size_t size, RetainPtr<Inode>&& inode, String&& name, bool is_readable, bool is_writable)
{
laddr.mask(PAGE_MASK);
size = PAGE_ROUND_UP(size);
// FIXME: This needs sanity checks. What if this overlaps existing regions?
if (laddr.is_null()) {
laddr = m_next_region;
m_next_region = m_next_region.offset(size).offset(PAGE_SIZE);
}
laddr.mask(0xfffff000);
m_regions.append(adopt(*new Region(laddr, size, move(inode), move(name), is_readable, is_writable)));
Range range;
if (laddr.is_null())
range = m_range_allocator.allocate_anywhere(size);
else
range = m_range_allocator.allocate_specific(laddr, size);
m_regions.append(adopt(*new Region(range.base(), range.size(), move(inode), move(name), is_readable, is_writable)));
MM.map_region(*this, *m_regions.last());
return m_regions.last().ptr();
}
Region* Process::allocate_region_with_vmo(LinearAddress laddr, size_t size, Retained<VMObject>&& vmo, size_t offset_in_vmo, String&& name, bool is_readable, bool is_writable)
{
laddr.mask(PAGE_MASK);
size = PAGE_ROUND_UP(size);
// FIXME: This needs sanity checks. What if this overlaps existing regions?
if (laddr.is_null()) {
laddr = m_next_region;
m_next_region = m_next_region.offset(size).offset(PAGE_SIZE);
}
laddr.mask(0xfffff000);
Range range;
if (laddr.is_null())
range = m_range_allocator.allocate_anywhere(size);
else
range = m_range_allocator.allocate_specific(laddr, size);
offset_in_vmo &= PAGE_MASK;
size = ceil_div(size, PAGE_SIZE) * PAGE_SIZE;
m_regions.append(adopt(*new Region(laddr, size, move(vmo), offset_in_vmo, move(name), is_readable, is_writable)));
m_regions.append(adopt(*new Region(range.base(), range.size(), move(vmo), offset_in_vmo, move(name), is_readable, is_writable)));
MM.map_region(*this, *m_regions.last());
return m_regions.last().ptr();
}
@ -119,6 +125,7 @@ bool Process::deallocate_region(Region& region)
InterruptDisabler disabler;
for (int i = 0; i < m_regions.size(); ++i) {
if (m_regions[i] == &region) {
m_range_allocator.deallocate({ region.laddr(), region.size() });
MM.unmap_region(region);
m_regions.remove(i);
return true;
@ -539,6 +546,9 @@ Process* Process::create_kernel_process(String&& name, void (*e)())
return process;
}
static const dword userspace_range_base = 0x01000000;
static const dword kernelspace_range_base = 0xc0000000;
Process::Process(String&& name, uid_t uid, gid_t gid, pid_t ppid, RingLevel ring, RetainPtr<Inode>&& cwd, RetainPtr<Inode>&& executable, TTY* tty, Process* fork_parent)
: m_name(move(name))
, m_pid(next_pid++) // FIXME: RACE: This variable looks racy!
@ -551,6 +561,7 @@ Process::Process(String&& name, uid_t uid, gid_t gid, pid_t ppid, RingLevel ring
, m_executable(move(executable))
, m_tty(tty)
, m_ppid(ppid)
, m_range_allocator(LinearAddress(userspace_range_base), kernelspace_range_base - userspace_range_base)
{
dbgprintf("Process: New process PID=%u with name=%s\n", m_pid, m_name.characters());