I had to change PhysicalPage around a bit for this. Physical pages can now
be instantiated for any arbitrary physical address without worrying that
such pages end up in the kernel page allocator when released.
Most of the pieces were already in place, I just glued everything together.
This is a monster patch that required changing a whole bunch of things.
There are performance and stability issues all over the place, but it works.
Pretty cool, I have to admit :^)
Maybe there will be other types of physical ranges to map in the future.
This API doesn't seem at all specific to framebuffers.
Also tidy up a bit in BochsVGADevice.
There's no need for an Inode to keep its corresponding VMObject alive.
Obviously there are huge benefits to keeping a filesystem cache,
but leaking everything is hardly the right strategy. :^)
- Don't cli() in Process::do_exec() unless current is execing.
Eventually this should go away once the scheduler is less retarded
in the face of interrupts.
- Improved memory access validation for ring0 processes.
We now look at the kernel ELF header to determine if an access
is appropriate. :^) It's very hackish but also kinda neat.
- Have Process::die() put the process into a new "Dying" state where
it can still get scheduled but no signals will be dispatched.
This way we can keep executing in die() but won't get our EIP
hijacked by signal dispatch. The main problem here was that die()
wanted to take various locks.
The current strategy is simply to nuke all physical pages and force
reload them from disk. This is obviously not optimal and should eventually
be optimized. It should be fairly straightforward.
Font now uses the same in-memory format as the font files we have on disk.
This allows us to simply mmap() the font files and not use any additional
memory for them. Very cool! :^)
Hacking on this exposed a bug in file-backed VMObjects where the first client
to instantiate a VMObject for a specific inode also got to decide its size.
Since file-backed VMObjects always have the same size as the underlying file,
this made no sense, so I removed the ability to even set a size in that case.
Turns out I had confused myself about the situation. Just because a page
has been paged in by another process doesn't mean that the *current*
process's page directory has the present bit set! D'oh. :^)
This exposed a serious race condition in page_in_from_inode().
Reordered the logic and added a paging lock to VMObject.
Now, only one process can page in from a VMObject at a time.
There are definitely ways to optimize this, for instance by making
the locking be per-page instead. It's not something that I'm going
to worry about right now though.
Previously, calling Region::commit() would make sure to allocate any missing
physical pages, but they would contain uninitialized data. This was very
obvious when allocating GraphicsBitmaps as they would have garbage pixels
rather than being filled with black.
The MM quickmap mechanism didn't work when operating on a non-active page
directory (which happens when we're in the middle of exec, for example.)
This patch changes quickmap to reside in the shared kernel page directory.
Also added some missing clobber lists to inline asm that I stumbled on.
Make PageDirectory retainable and have each Region co-own the PageDirectory
they're mapped into. When unmapped, Region has no associated PageDirectory.
This allows Region to automatically unmap itself when destroyed.
The system can finally idle without burning CPU. :^)
There are some issues with scheduling making the mouse cursor sloppy
and unresponsive that need to be dealt with.
The old approach only worked because of an overpermissive accident.
There's now a concept of supervisor physical pages that can be allocated.
They all sit in the low 4 MB of physical memory and are identity mapped,
shared between all processes, and only ring 0 can access them.
This container is really just there to keep a retain on the individual
PhysicalPages for each page table. A HashMap does the job with far greater
space efficiency.
Process page directories can now actually be freed. This could definitely
be implemented in a nicer, less wasteful way, but this works for now.
The spawn stress test can now run for a lot longer but eventually dies
due to kmalloc running out of memory.
mmap() will now map uncommitted pages that get allocated and zeroed upon the
first access. I also made /proc/PID/vm show number of "committed" bytes in
each region. This is so cool! :^)
...by adding a new class called Ext2Inode that inherits CoreInode.
The idea is that a vnode will wrap a CoreInode rather than InodeIdentifier.
Each CoreInode subclass can keep whatever caches they like.
Right now, Ext2Inode caches the list of block indices since it can be very
expensive to retrieve.
- Process::exec() needs to restore the original paging scope when called
on a non-current process.
- Add missing InterruptDisabler guards around g_processes access.
- Only flush the TLB when modifying the active page tables.
This is really sweet! :^) The four instances of /bin/sh spawned at
startup now share their read-only text pages.
There are problems and limitations here, and plenty of room for
improvement. But it kinda works.
