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Kernel: Make Region splitting OOM-safe

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Region allocation failures during splitting are now propagated all the
way out to where we can return ENOMEM for them.
This commit is contained in:
Andreas Kling 2021-07-11 18:51:54 +02:00
parent cac557eee0
commit cd7a49b90d
Notes: sideshowbarker 2024-07-18 09:19:09 +09:00 
Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/cd7a49b90d6
3 changed files with 40 additions and 16 deletions
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22
Kernel/Syscalls/mmap.cpp
View file

@ -341,10 +341,16 @@ KResultOr<FlatPtr> Process::sys$mprotect(Userspace<void*> addr, size_t size, int
// This vector is the region(s) adjacent to our range.
// We need to allocate a new region for the range we wanted to change permission bits on.
auto adjacent_regions = space().split_region_around_range(*region, range_to_mprotect);
auto adjacent_regions_or_error = space().try_split_region_around_range(*region, range_to_mprotect);
if (adjacent_regions_or_error.is_error())
return adjacent_regions_or_error.error();
auto& adjacent_regions = adjacent_regions_or_error.value();
size_t new_range_offset_in_vmobject = region->offset_in_vmobject() + (range_to_mprotect.base().get() - region->range().base().get());
auto& new_region = space().allocate_split_region(*region, range_to_mprotect, new_range_offset_in_vmobject);
auto new_region_or_error = space().try_allocate_split_region(*region, range_to_mprotect, new_range_offset_in_vmobject);
if (new_region_or_error.is_error())
return new_region_or_error.error();
auto& new_region = *new_region_or_error.value();
new_region.set_readable(prot & PROT_READ);
new_region.set_writable(prot & PROT_WRITE);
new_region.set_executable(prot & PROT_EXEC);
@ -399,12 +405,20 @@ KResultOr<FlatPtr> Process::sys$mprotect(Userspace<void*> addr, size_t size, int
// This vector is the region(s) adjacent to our range.
// We need to allocate a new region for the range we wanted to change permission bits on.
auto adjacent_regions = space().split_region_around_range(*old_region, intersection_to_mprotect);
auto adjacent_regions_or_error = space().try_split_region_around_range(*old_region, intersection_to_mprotect);
if (adjacent_regions_or_error.is_error())
return adjacent_regions_or_error.error();
auto& adjacent_regions = adjacent_regions_or_error.value();
// there should only be one
VERIFY(adjacent_regions.size() == 1);
size_t new_range_offset_in_vmobject = old_region->offset_in_vmobject() + (intersection_to_mprotect.base().get() - old_region->range().base().get());
auto& new_region = space().allocate_split_region(*region, intersection_to_mprotect, new_range_offset_in_vmobject);
auto new_region_or_error = space().try_allocate_split_region(*region, intersection_to_mprotect, new_range_offset_in_vmobject);
if (new_region_or_error.is_error())
return new_region_or_error.error();
auto& new_region = *new_region_or_error.value();
new_region.set_readable(prot & PROT_READ);
new_region.set_writable(prot & PROT_WRITE);
new_region.set_executable(prot & PROT_EXEC);

30
Kernel/VM/Space.cpp
View file

@ -74,7 +74,10 @@ KResult Space::unmap_mmap_range(VirtualAddress addr, size_t size)
// We manually unmap the old region here, specifying that we *don't* want the VM deallocated.
region->unmap(Region::ShouldDeallocateVirtualMemoryRange::No);
auto new_regions = split_region_around_range(*region, range_to_unmap);
auto new_regions_or_error = try_split_region_around_range(*region, range_to_unmap);
if (new_regions_or_error.is_error())
return new_regions_or_error.error();
auto& new_regions = new_regions_or_error.value();
// Instead we give back the unwanted VM manually.
page_directory().range_allocator().deallocate(range_to_unmap);
@ -119,7 +122,11 @@ KResult Space::unmap_mmap_range(VirtualAddress addr, size_t size)
region->unmap(Region::ShouldDeallocateVirtualMemoryRange::No);
// Otherwise just split the regions and collect them for future mapping
if (new_regions.try_extend(split_region_around_range(*region, range_to_unmap)))
auto split_regions_or_error = try_split_region_around_range(*region, range_to_unmap);
if (split_regions_or_error.is_error())
return split_regions_or_error.error();
if (new_regions.try_extend(split_regions_or_error.value()))
return ENOMEM;
}
// Instead we give back the unwanted VM manually at the end.
@ -143,12 +150,12 @@ Optional<Range> Space::allocate_range(VirtualAddress vaddr, size_t size, size_t
return page_directory().range_allocator().allocate_specific(vaddr, size);
}
Region& Space::allocate_split_region(const Region& source_region, const Range& range, size_t offset_in_vmobject)
KResultOr<Region*> Space::try_allocate_split_region(Region const& source_region, Range const& range, size_t offset_in_vmobject)
{
auto new_region = Region::try_create_user_accessible(
m_process, range, source_region.vmobject(), offset_in_vmobject, KString::try_create(source_region.name()), source_region.access(), source_region.is_cacheable() ? Region::Cacheable::Yes : Region::Cacheable::No, source_region.is_shared());
// FIXME: Handle !new_region (by propagating ENOMEM)
VERIFY(new_region);
if (!new_region)
return ENOMEM;
auto& region = add_region(new_region.release_nonnull());
region.set_syscall_region(source_region.is_syscall_region());
region.set_mmap(source_region.is_mmap());
@ -158,7 +165,7 @@ Region& Space::allocate_split_region(const Region& source_region, const Range& r
if (source_region.should_cow(page_offset_in_source_region + i))
region.set_should_cow(i, true);
}
return region;
return &region;
}
KResultOr<Region*> Space::allocate_region(Range const& range, StringView name, int prot, AllocationStrategy strategy)
@ -286,20 +293,23 @@ Region& Space::add_region(NonnullOwnPtr<Region> region)
}
// Carve out a virtual address range from a region and return the two regions on either side
Vector<Region*, 2> Space::split_region_around_range(const Region& source_region, const Range& desired_range)
KResultOr<Vector<Region*, 2>> Space::try_split_region_around_range(const Region& source_region, const Range& desired_range)
{
Range old_region_range = source_region.range();
auto remaining_ranges_after_unmap = old_region_range.carve(desired_range);
VERIFY(!remaining_ranges_after_unmap.is_empty());
auto make_replacement_region = [&](const Range& new_range) -> Region& {
auto try_make_replacement_region = [&](const Range& new_range) -> KResultOr<Region*> {
VERIFY(old_region_range.contains(new_range));
size_t new_range_offset_in_vmobject = source_region.offset_in_vmobject() + (new_range.base().get() - old_region_range.base().get());
return allocate_split_region(source_region, new_range, new_range_offset_in_vmobject);
return try_allocate_split_region(source_region, new_range, new_range_offset_in_vmobject);
};
Vector<Region*, 2> new_regions;
for (auto& new_range : remaining_ranges_after_unmap) {
new_regions.unchecked_append(&make_replacement_region(new_range));
auto new_region_or_error = try_make_replacement_region(new_range);
if (new_region_or_error.is_error())
return new_region_or_error.error();
new_regions.unchecked_append(new_region_or_error.value());
}
return new_regions;
}

4
Kernel/VM/Space.h
View file

@ -42,8 +42,8 @@ public:
bool deallocate_region(Region& region);
OwnPtr<Region> take_region(Region& region);
Region& allocate_split_region(const Region& source_region, const Range&, size_t offset_in_vmobject);
Vector<Region*, 2> split_region_around_range(const Region& source_region, const Range&);
KResultOr<Region*> try_allocate_split_region(Region const& source_region, Range const&, size_t offset_in_vmobject);
KResultOr<Vector<Region*, 2>> try_split_region_around_range(Region const& source_region, Range const&);
Region* find_region_from_range(const Range&);
Region* find_region_containing(const Range&);