- Mutex test added. Forked tasks demonstrate produce/consumer using a
shared mmap'ed page.
- Added l4lib assembler syscall
- Added forgotten SWI to mutex control offset in syscall page.
- Added mutex head initialization
- Contended child successfully sleeps in a waitqueue.
Issues:
- Somehow the child's produced page buffer is altered at about [4020] offset.
Parent fails to validate buffer therefore.
- Need to add syncing to test so that parent does not unlock and lock again
before child has a chance to lock buffer and produce.
- Compiles and Codezero runs as normal without touching mutex implementation
- Mutex implementation needs testing.
The mutex control syscall allows userspace programs to declare any virtual
address as a mutex lock and ask for help from the kernel syscall
for resolving locking contentions.
Previously during ipc copy, only the currently active task flags were
checked. This means the flags of whoever doing the actual copy was used
in the ipc. Now flags are stored in the ktcb and checked by the copy routine.
Current use of the flags is to determine short/full/extended ipc.
- Test0 has a full ipc mr read/write test.
- A full ipc occurs for definite only if both parties use the FULL IPC flag.
Otherwise the thread that makes the ipc copy rules on whether it was a short
or a full copy.
- Added a full ipc send/recv test
- Removed non-zero value checking in r2 for ipc that was there
to catch inadvertent full ipc calls.
- Added correct hanlding for read/write mrs for current status of utcb.
TODO:
- Add mapping of every utcb to every task for privileged access so that
the kernel can access every utcb without switching spaces.
- Removal of same mappings
- Upon thread creation need to copy page tables accordingly i.e.
each task will have its own utcb mapped with USER access, but every
other utcb as kernel access only. Need to handle this case upon page
table copying.
- Proper releasing of user pmd and pgds when a space is not used.
- Proper releasing of task, space ids.
- At occasions a starting thread gets bogus SPSR, this needs investigating.
- At a very rare occasion arch_setup_new_thread() had a kernel data abort during
register copying from one task to another. Needs investigating.
- Fixed potential concurrency bugs due to preemption being enabled.
- Introduced a new address space structure to better account for
address spaces and page tables.
- Currently executes fine up to forking. Will investigate.
- KIP's pointer to UTCB seems to work with existing l4lib ipc functions.
- Works up to clone()
- In clone we mmap() the same UTCB on each new thread - excessive.
- Generally during page fault handling, cloned threads may fault on the same page
multiple times even though a single handling would be enough for all of them.
Need to detect and handle this.
Increased inode block pointers to 40. The current maximum allowed (and checked).
Updates to file size after every file write ensures subsequent writes can
correctly operate using updated file size information (i.e. not try to add
more pages that are already present). We cannot do this inside write() because
directory writes rely on byte-granularity updates on file buffers, whereas
file updates are by page-granularity (currently).
It turned out we used one version of kmalloc for malloc() and another for kfree()!
Now fixed.
Added parent-child relationship to tasks. Need to polish handling CLONE_PARENT and THREAD.
l4_unmap now returns -1 if given range was only partially unmapped.
do_munmap() now only unmaps address ranges that have correspondence in
the unmapped vmas. Trying to unmap regions with no correspondent vmas
causes problems in corner cases, e.g. mm0 that tries to mmap its own
address space during initialisation would unmap its whole address space
and fail to execute.
File open was failing when using 2 files with same name. TODO: Look at it in the future.
Need to increase writeable file size in fs0. 16 pages don't work.
A new scheduler replaces the old one.
- There are no sched_xxx_notify() calls that ask scheduler to change task state.
- Tasks now have priorities and different timeslices.
- One second interval is distributed among processes.
- There are just runnable and expired queues.
- SCHED_GRANULARITY determines a maximum running boundary for tasks.
- Scheduler can now detect a safe point and suspend a task.
Interruptible blocking is implemented.
- Mutexes, waitqueues and ipc are modified to have an interruptible nature.
- Sleep information is stored on the ktcb. (which waitqueue? etc.)
- Added automatic utcb map/prefaulting of forked tasks for fs0
so that it does not need to explicitly request those tasks from mm0.
Eliminating fs0 requests to mm0 reduce deadlock possibilities.
- Replaced kmalloc with a public malloc implementation because of a bug in kmalloc.
- Fixed a kfree bug. default_release_pages was trying to free page_array pages.
- Adding prefaulting of fs0 to avoid page fault deadlocks.
- Fixed a bug that a vmo page_cache equivalence would simply drop a link to
an original vmo, even if the vmo could have more pages outside the page cache,
or if the vmo was not a shadow vmo.
- Fixed a bug with page allocator where recursion would corrupt global variables.
- Now going to fix or re-write a simpler page allocator that works.
Normally common kernel entries in 2nd level page table need not get
copied to new tasks since those entries will be used commonly by all tasks.
On fork, we were copying those unnecessarily.
Child needs rewound function stack in order to reach registers r9-r12
that have original userspace values. But we jump to return_from_syscall
without rewinding the stack. Therefore to ease context restore, we save
r9-r12 on the stack as well upon syscall entry.
This copies the parent kernel stack to child only for the part where
the previous context is saved. Then the child registers are modified
so that it would begin execution from returning of the system call.
sys_timer accumulates timer ticks into seconds, minutes, hours and days.
It's left to the user to calculate from days into a date. It is not yet
known if the calculation is even roughly correct.
Reduced 2 kmem_reclaim/grant calls into one kmem_control call.
Tasks boot fine up to doing ipc using their utcbs.
UTCB PLAN:
- Push ipc registers into private environment instead of a shared utcb,
but map-in a shared utcb to pass on long data to server tasks.
- Shared utcb has unique virtual address for every thread.
- Forked child does inherit parent's utcb, but cannot use it to communicate to
any server. It must explicitly obtain its own utcb for that.
- Clone could have a flag to explicitly not inherit parent utcb, which is the
right thing to do.
- MM0 serves a syscall to obtain self utcb.
- By this method, upon forks tasks don't need to map-in a utcb unless they want
to pass long data.
Next issues: For every read fault, the fault must traverse the
vma's object stack until the page is found. The problem was that
we were only searching the first object, that object was a writable
shadow, and the shadow didn't have the read-only page, and the 0
return value was interpreted with IS_ERR() and failed, so address
0 was mapped into the location, and QEMU blew off.
utcb as a shared page instead of the message registers.
Implemented the code that passes task information from mm0 to fs0
using the fs0 utcb. The code seems to work OK but:
There's an issue with anon pages that they end up on the same swapfile
and with same file offsets (e.g. utcb and stack at offset 0). Need to
fix this issue but otherwise this implementation seems to work.
TODO:
- Separate anon regions into separate vmfiles.
- Possibly map the stacks from virtual files so that they can be
read from userspace in the future for debugging.
- Possibly utcb could be created as a shared memory object using shmget/shmat
during startup.
Environment is backed by a special per-task file maintained by mm0 for each task.
This file is filled in by the env pager, by simple copying of env data into the
faulty page upon a fault. UTCB and all anon regions (stack) could use the same
scheme.
Fixed IS_ERR(x) to accept negative values that are above -1000 for errors. This
protects against false positives for pointers such as 0xE0000000.
modified: include/l4/generic/scheduler.h
modified: include/l4/macros.h
modified: src/arch/arm/exception.c
modified: tasks/fs0/include/linker.lds
modified: tasks/libl4/src/init.c
modified: tasks/libposix/shm.c
new file: tasks/mm0/include/env.h
modified: tasks/mm0/include/file.h
new file: tasks/mm0/include/lib/addr.h
deleted: tasks/mm0/include/lib/vaddr.h
modified: tasks/mm0/include/task.h
new file: tasks/mm0/include/utcb.h
new file: tasks/mm0/src/env.c
modified: tasks/mm0/src/fault.c
modified: tasks/mm0/src/file.c
modified: tasks/mm0/src/init.c
new file: tasks/mm0/src/lib/addr.c
modified: tasks/mm0/src/lib/idpool.c
deleted: tasks/mm0/src/lib/vaddr.c
modified: tasks/mm0/src/mmap.c
modified: tasks/mm0/src/shm.c
modified: tasks/mm0/src/task.c
new file: tasks/mm0/src/utcb.c
modified: tasks/test0/include/linker.lds
Headers 3 headers related to message registers and utcbs are now merged under
utcb.h in libl4. Some message register definitions used by the kernel are now
moved into kernel's glue/message.h. This avoids the duplication of same
definitions. Also the total number of mregs are now determined by arch-specific
kernel header, which is good.
