I believe this to be safe, as the main thing that LockRefPtr provides
over RefPtr is safe copying from a shared LockRefPtr instance. I've
inspected the uses of RefPtr<PhysicalPage> and it seems they're all
guarded by external locking. Some of it is less obvious, but this is
an area where we're making continuous headway.
You're still required to disable interrupts though, as the mappings are
per-CPU. This exposed the fact that our CR3 lookup map is insufficiently
protected (but we'll address that in a separate commit.)
Until now, our kernel has reimplemented a number of AK classes to
provide automatic internal locking:
- RefPtr
- NonnullRefPtr
- WeakPtr
- Weakable
This patch renames the Kernel classes so that they can coexist with
the original AK classes:
- RefPtr => LockRefPtr
- NonnullRefPtr => NonnullLockRefPtr
- WeakPtr => LockWeakPtr
- Weakable => LockWeakable
The goal here is to eventually get rid of the Lock* classes in favor of
using external locking.
As soon as we've saved CR2 (the faulting address), we can re-enable
interrupt processing. This should make the kernel more responsive under
heavy fault loads.
Uncommitted pages (shared zero pages) can not contain any existing data
and can not be modified, so there's no point to committing a bunch of
extra pages to cover for them in the forked child.
Since both the parent process and child process hold a reference to the
COW committed set, once the child process exits, the committed COW
pages are effectively leaked, only being slowly re-claimed each time
the parent process writes to one of them, realizing it's no longer
shared, and uncommitting it.
In order to mitigate this we now hold a weak reference the parent
VMObject from which the pages are cloned, and we use it on destruction
when available to drop the reference to the committed set from it as
well.
If someone specifically wants contiguous memory in the low-physical-
address-for-DMA range ("super pages"), they can use the
allocate_dma_buffer_pages() helper.
This commit moves the allocation of the resources required for
AnonymousVMObject from its constructors to its factory functions.
We're making this change to expose the fallibility of the allocation.
This commit moves the allocation of the resources required for VMObject
from its constructors to the constructors of its child classes.
We're making this change to give the child classes the chance to expose
the fallibility of the allocation.
We now use AK::Error and AK::ErrorOr<T> in both kernel and userspace!
This was a slightly tedious refactoring that took a long time, so it's
not unlikely that some bugs crept in.
Nevertheless, it does pass basic functionality testing, and it's just
real nice to finally see the same pattern in all contexts. :^)
And also try_create<T> => try_make_ref_counted<T>.
A global "create" was a bit much. The new name matches make<T> better,
which we've used for making single-owner objects since forever.
The quickmap_page() and unquickmap_page() functions are used to map a
single physical page at a kernel virtual address for temporary access.
These use the per-CPU quickmap buffer in the page tables, and access to
this is guarded by the MM lock. To prevent bugs, quickmap_page() should
not *take* the MM lock, but rather verify that it is already held!
This exposed two situations where we were using quickmap without holding
the MM lock during page fault handling. This patch is forced to fix
these issues (which is great!) :^)
This makes for nicer handling of errors compared to checking whether a
RefPtr is null. Additionally, this will give way to return different
types of errors in the future.
