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/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/NonnullRefPtr.h>
#include <AK/RefPtr.h>
#include <Kernel/Assertions.h>
#include <Kernel/Random.h>
#include <Kernel/VM/PhysicalRegion.h>
namespace Kernel {
PhysicalRegion::PhysicalRegion(PhysicalAddress lower, PhysicalAddress upper)
: m_lower(lower)
, m_upper(upper)
{
}
void PhysicalRegion::expand(PhysicalAddress lower, PhysicalAddress upper)
{
VERIFY(!m_pages);
m_lower = lower;
m_upper = upper;
}
unsigned PhysicalRegion::finalize_capacity()
{
VERIFY(!m_pages);
m_pages = (m_upper.get() - m_lower.get()) / PAGE_SIZE;
m_bitmap.grow(m_pages, false);
return size();
}
PhysicalRegion PhysicalRegion::take_pages_from_beginning(unsigned page_count)
{
VERIFY(m_used == 0);
VERIFY(page_count > 0);
VERIFY(page_count < m_pages);
auto taken_lower = m_lower;
auto taken_upper = taken_lower.offset((PhysicalPtr)page_count * PAGE_SIZE);
m_lower = m_lower.offset((PhysicalPtr)page_count * PAGE_SIZE);
// TODO: find a more elegant way to re-init the existing region
m_pages = 0;
m_bitmap = {}; // FIXME: Kind of wasteful
finalize_capacity();
auto taken_region = create(taken_lower, taken_upper);
taken_region.finalize_capacity();
return taken_region;
}
NonnullRefPtrVector<PhysicalPage> PhysicalRegion::take_contiguous_free_pages(size_t count, bool supervisor, size_t physical_alignment)
{
VERIFY(m_pages);
VERIFY(m_used != m_pages);
NonnullRefPtrVector<PhysicalPage> physical_pages;
physical_pages.ensure_capacity(count);
auto first_contiguous_page = find_contiguous_free_pages(count, physical_alignment);
for (size_t index = 0; index < count; index++)
physical_pages.append(PhysicalPage::create(m_lower.offset(PAGE_SIZE * (index + first_contiguous_page)), supervisor));
return physical_pages;
}
unsigned PhysicalRegion::find_contiguous_free_pages(size_t count, size_t physical_alignment)
{
VERIFY(count != 0);
VERIFY(physical_alignment % PAGE_SIZE == 0);
// search from the last page we allocated
auto range = find_and_allocate_contiguous_range(count, physical_alignment / PAGE_SIZE);
VERIFY(range.has_value());
return range.value();
}
Optional<unsigned> PhysicalRegion::find_one_free_page()
{
if (m_used == m_pages) {
// We know we don't have any free pages, no need to check the bitmap
// Check if we can draw one from the return queue
if (m_recently_returned.size() > 0) {
u8 index = get_fast_random<u8>() % m_recently_returned.size();
Checked<PhysicalPtr> local_offset = m_recently_returned[index].get();
local_offset -= m_lower.get();
m_recently_returned.remove(index);
VERIFY(!local_offset.has_overflow());
VERIFY(local_offset.value() < (FlatPtr)(m_pages * PAGE_SIZE));
return local_offset.value() / PAGE_SIZE;
}
return {};
}
auto free_index = m_bitmap.find_one_anywhere_unset(m_free_hint);
if (!free_index.has_value())
return {};
auto page_index = free_index.value();
m_bitmap.set(page_index, true);
m_used++;
m_free_hint = free_index.value() + 1; // Just a guess
if (m_free_hint >= m_bitmap.size())
m_free_hint = 0;
return page_index;
}
Optional<unsigned> PhysicalRegion::find_and_allocate_contiguous_range(size_t count, unsigned alignment)
{
VERIFY(count != 0);
size_t found_pages_count = 0;
// TODO: Improve how we deal with alignment != 1
auto first_index = m_bitmap.find_longest_range_of_unset_bits(count + alignment - 1, found_pages_count);
if (!first_index.has_value())
return {};
auto page = first_index.value();
if (alignment != 1) {
auto lower_page = m_lower.get() / PAGE_SIZE;
page = ((lower_page + page + alignment - 1) & ~(alignment - 1)) - lower_page;
}
if (found_pages_count >= count) {
m_bitmap.set_range<true>(page, count);
m_used += count;
m_free_hint = first_index.value() + count + 1; // Just a guess
if (m_free_hint >= m_bitmap.size())
m_free_hint = 0;
return page;
}
return {};
}
RefPtr<PhysicalPage> PhysicalRegion::take_free_page(bool supervisor)
{
VERIFY(m_pages);
auto free_index = find_one_free_page();
if (!free_index.has_value())
return nullptr;
return PhysicalPage::create(m_lower.offset((PhysicalPtr)free_index.value() * PAGE_SIZE), supervisor);
}
void PhysicalRegion::free_page_at(PhysicalAddress addr)
{
VERIFY(m_pages);
if (m_used == 0) {
VERIFY_NOT_REACHED();
}
Checked<PhysicalPtr> local_offset = addr.get();
local_offset -= m_lower.get();
VERIFY(!local_offset.has_overflow());
VERIFY(local_offset.value() < ((PhysicalPtr)m_pages * PAGE_SIZE));
auto page = local_offset.value() / PAGE_SIZE;
m_bitmap.set(page, false);
m_free_hint = page; // We know we can find one here for sure
m_used--;
}
void PhysicalRegion::return_page(PhysicalAddress paddr)
{
auto returned_count = m_recently_returned.size();
if (returned_count >= m_recently_returned.capacity()) {
// Return queue is full, pick a random entry and free that page
// and replace the entry with this page
auto& entry = m_recently_returned[get_fast_random<u8>()];
free_page_at(entry);
entry = paddr;
} else {
// Still filling the return queue, just append it
m_recently_returned.append(paddr);
}
}
}
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