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memory: replace live direct mappings without exposing an inaccessible gap

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This commit is contained in:
nmzik
2026-10-04 08:16:28 +04:00
parent 1f6be3d570
commit 46900d8042
4 changed files with 279 additions and 53 deletions
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src/kernel/memoryAddressSpace.inc
+60 -38
View File
@@ -231,9 +231,8 @@ public:
return true;
}
bool MapExistingPlaceholderFixed(uint64_t vaddr, uint64_t size, uint64_t backing_offset,
VirtualMemory::Mode mode,
FailureReason* failure_reason = nullptr) {
bool MapFixed(uint64_t vaddr, uint64_t size, uint64_t backing_offset,
VirtualMemory::Mode mode, FailureReason* failure_reason = nullptr) {
if (!IsAvailable() || !RangeOk(backing_offset, size)) {
SetFailure(failure_reason, !IsAvailable() ? FailureReason::BackingUnavailable
: FailureReason::PhysicalRangeOutOfBounds);
@@ -257,14 +256,13 @@ public:
SetFailure(failure_reason, FailureReason::None);
return true;
#else
std::lock_guard lock(m_mutex);
void* mapped = MapView(vaddr, size, backing_offset, mode, failure_reason);
if (mapped == nullptr || reinterpret_cast<uint64_t>(mapped) != vaddr) {
return false;
}
{
std::lock_guard lock(m_mutex);
EXIT_IF(!m_maps.emplace(vaddr, MapEntry {vaddr, size, backing_offset, mode}).second);
}
RemoveMappingsUnlocked(vaddr, size);
EXIT_IF(!m_maps.emplace(vaddr, MapEntry {vaddr, size, backing_offset, mode}).second);
SetFailure(failure_reason, FailureReason::None);
return true;
#endif
@@ -302,8 +300,7 @@ public:
bool part_placeholder_preserved = false;
if (!UnmapOne(entry.vaddr, entry.size, &part_placeholder_preserved)) {
for (auto it = removed.rbegin(); it != removed.rend(); ++it) {
EXIT_IF(!MapExistingPlaceholderFixed(it->vaddr, it->size, it->backing_offset,
it->mode));
EXIT_IF(!MapFixed(it->vaddr, it->size, it->backing_offset, it->mode));
}
if (placeholder_preserved != nullptr) {
*placeholder_preserved = false;
@@ -320,8 +317,7 @@ public:
// views into one placeholder before publishing it there.
if (removed.size() > 1 && !CoalescePlaceholders(vaddr, size)) {
for (auto it = removed.rbegin(); it != removed.rend(); ++it) {
EXIT_IF(!MapExistingPlaceholderFixed(it->vaddr, it->size, it->backing_offset,
it->mode));
EXIT_IF(!MapFixed(it->vaddr, it->size, it->backing_offset, it->mode));
}
return false;
}
@@ -363,12 +359,10 @@ public:
return false;
}
#if KYTY_PLATFORM == KYTY_PLATFORM_WINDOWS
const uint64_t left_size = vaddr - old.vaddr;
const uint64_t right_addr = vaddr + size;
const uint64_t old_end = old.vaddr + old.size;
const uint64_t right_size = old_end - right_addr;
#if KYTY_PLATFORM == KYTY_PLATFORM_WINDOWS
const uint64_t right_size = old.vaddr + old.size - right_addr;
const bool exact_unmap = (vaddr == old.vaddr && size == old.size);
if (exact_unmap) {
const bool unmapped =
@@ -393,14 +387,11 @@ public:
ok = SplitPlaceholder(vaddr, size) && ok;
}
if (left_size != 0) {
ok = MapExistingPlaceholderFixed(old.vaddr, left_size, old.backing_offset,
old.mode) &&
ok;
ok = MapFixed(old.vaddr, left_size, old.backing_offset, old.mode) && ok;
}
if (right_size != 0) {
ok = MapExistingPlaceholderFixed(right_addr, right_size,
old.backing_offset + (right_addr - old.vaddr),
old.mode) &&
ok = MapFixed(right_addr, right_size,
old.backing_offset + (right_addr - old.vaddr), old.mode) &&
ok;
}
if (ok) {
@@ -418,8 +409,7 @@ public:
}
EXIT_IF(VirtualFree(reinterpret_cast<void*>(old.vaddr), old.size,
MEM_RELEASE | MEM_COALESCE_PLACEHOLDERS) == 0);
EXIT_IF(
!MapExistingPlaceholderFixed(old.vaddr, old.size, old.backing_offset, old.mode));
EXIT_IF(!MapFixed(old.vaddr, old.size, old.backing_offset, old.mode));
return false;
}
std::lock_guard lock(m_mutex);
@@ -433,16 +423,7 @@ public:
}
std::lock_guard lock(m_mutex);
m_maps.erase(old.vaddr);
if (left_size != 0) {
m_maps.emplace(old.vaddr,
MapEntry {old.vaddr, left_size, old.backing_offset, old.mode});
}
if (right_size != 0) {
m_maps.emplace(right_addr,
MapEntry {right_addr, right_size,
old.backing_offset + right_addr - old.vaddr, old.mode});
}
RemoveMappingsUnlocked(vaddr, size);
if (placeholder_preserved != nullptr) {
*placeholder_preserved = true;
@@ -516,6 +497,33 @@ private:
VirtualMemory::Mode mode = VirtualMemory::Mode::NoAccess;
};
#if KYTY_PLATFORM == KYTY_PLATFORM_LINUX
void RemoveMappingsUnlocked(uint64_t vaddr, uint64_t size) {
const auto end = vaddr + size;
auto it = m_maps.upper_bound(vaddr);
if (it != m_maps.begin()) {
--it;
}
while (it != m_maps.end() && it->first < end) {
const auto old = it->second;
const auto old_end = old.vaddr + old.size;
if (old_end <= vaddr) {
++it;
continue;
}
it = m_maps.erase(it);
if (old.vaddr < vaddr) {
m_maps.emplace(old.vaddr,
MapEntry {old.vaddr, vaddr - old.vaddr, old.backing_offset, old.mode});
}
if (end < old_end) {
m_maps.emplace(end, MapEntry {end, old_end - end,
old.backing_offset + end - old.vaddr, old.mode});
}
}
}
#endif
bool FindContainingUnlocked(uint64_t vaddr, uint64_t size, MapEntry* out) const {
EXIT_IF(out == nullptr);
@@ -621,6 +629,12 @@ private:
void* MapView(uint64_t vaddr, uint64_t size, uint64_t backing_offset, VirtualMemory::Mode mode,
FailureReason* failure_reason) {
#if defined(KYTY_VIRTUAL_MEMORY_ALLOCATION_TESTS)
if (const auto callback = g_test_before_backing_map) {
g_test_before_backing_map = nullptr;
callback(vaddr, size);
}
#endif
void* ptr = mmap(reinterpret_cast<void*>(vaddr), size, GetProtect(mode),
MAP_SHARED | MAP_FIXED, m_fd, static_cast<off_t>(backing_offset));
if (ptr == MAP_FAILED) {
@@ -778,7 +792,12 @@ public:
VirtualMemory::Mode mode,
GuestBackingStore::FailureReason* failure_reason = nullptr) {
std::lock_guard lock(m_mutex);
if (!ConsumeUnlocked(vaddr, size)) {
#if KYTY_PLATFORM == KYTY_PLATFORM_LINUX
const bool replacing = ContainsMappedUnlocked(vaddr, size, MappingType::Backing);
#else
constexpr bool replacing = false;
#endif
if (!replacing && !ConsumeUnlocked(vaddr, size)) {
if (failure_reason != nullptr) {
*failure_reason = GuestBackingStore::FailureReason::AddressRangeUnavailable;
}
@@ -787,12 +806,15 @@ public:
const auto host_mode = VirtualMemory::IsExecute(mode)
? VirtualMemory::Mode::ExecuteReadWrite
: VirtualMemory::Mode::ReadWrite;
if (m_backing->MapExistingPlaceholderFixed(vaddr, size, backing_offset, host_mode,
failure_reason)) {
EXIT_IF(!AddMappedUnlocked(vaddr, size, MappingType::Backing));
if (m_backing->MapFixed(vaddr, size, backing_offset, host_mode, failure_reason)) {
if (!replacing) {
EXIT_IF(!AddMappedUnlocked(vaddr, size, MappingType::Backing));
}
return true;
}
AddFreeUnlocked(vaddr, size);
if (!replacing) {
AddFreeUnlocked(vaddr, size);
}
return false;
}