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kernel/memory: reserve only available guest address ranges on Linux

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Reserve only free guest address ranges
This commit is contained in:
nikosszzz
2026-08-02 03:24:30 +02:00
committed by nmzik
parent cb6ead58dc
commit 89e12b04c8
1 changed files with 58 additions and 9 deletions
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src/kernel/memoryAddressSpace.inc
+58 -9
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@@ -1058,24 +1058,73 @@ private:
{HOST_SYSTEM_RESERVED_MIN, HOST_SYSTEM_RESERVED_MAX + 1u},
{HOST_USER_MIN, HOST_USER_MAX + 1u},
}};
for (const auto& [start, end]: regions) {
int flags = MAP_PRIVATE | MAP_ANON | MAP_NORESERVE;
std::vector<std::pair<uint64_t, uint64_t>> occupied;
FILE* maps = fopen("/proc/self/maps", "r");
EXIT_IF(maps == nullptr);
char line[512];
while (fgets(line, sizeof(line), maps) != nullptr) {
unsigned long long mapping_start = 0;
unsigned long long mapping_end = 0;
if (sscanf(line, "%llx-%llx", &mapping_start, &mapping_end) == 2) {
occupied.emplace_back(static_cast<uint64_t>(mapping_start),
static_cast<uint64_t>(mapping_end));
}
}
fclose(maps);
auto reserve_range = [this](uint64_t start, uint64_t end) {
start = AlignUp(start, PageSize());
end = AlignDown(end, PageSize());
if (start == 0 || end <= start) {
return;
}
const auto size = end - start;
int flags = MAP_PRIVATE | MAP_ANON | MAP_NORESERVE;
#if defined(KYTY_LINKED_GUEST_ADDRESS_SPACE)
flags |= MAP_FIXED;
#elif defined(MAP_FIXED_NOREPLACE)
flags |= MAP_FIXED_NOREPLACE;
#endif
void* ptr = mmap(reinterpret_cast<void*>(start), end - start, PROT_NONE, flags, -1, 0);
void* ptr = mmap(reinterpret_cast<void*>(start), size, PROT_NONE, flags, -1, 0);
if (ptr == MAP_FAILED || reinterpret_cast<uint64_t>(ptr) != start) {
if (ptr != MAP_FAILED) {
munmap(ptr, end - start);
munmap(ptr, size);
}
EXIT("failed to reserve guest address space at 0x%016" PRIx64 ", size 0x%016" PRIx64
"\n",
start, end - start);
return;
}
AddFreeUnlocked(start, size);
m_owned.emplace_back(start, size);
};
for (const auto& [region_start, region_end]: regions) {
auto current = region_start;
for (const auto& [mapping_start, mapping_end]: occupied) {
if (mapping_end <= current) {
continue;
}
if (mapping_start >= region_end) {
break;
}
if (mapping_start > current) {
reserve_range(current, std::min(mapping_start, region_end));
}
current = std::max(current, mapping_end);
if (current >= region_end) {
break;
}
}
if (current < region_end) {
reserve_range(current, region_end);
}
AddFreeUnlocked(start, end - start);
m_owned.emplace_back(start, end - start);
}
#endif
}