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Ville Juven 09e7987121 sched/addrenv: Fix system crash when process group has been deleted 
There is currently a big problem in the address environment handling which
is that the address environment is released too soon when the process is
exiting. The current MMU mappings will always be the exiting process's, which means
the system needs them AT LEAST until the next context switch happens. If
the next thread is a kernel thread, the address environment is needed for
longer.

Kernel threads "lend" the address environment of the previous user process.
This is beneficial in two ways:
- The kernel processes do not need an allocated address environment
- When a context switch happens from user -> kernel or kernel -> kernel,
  the TLB does not need to be flushed. This must be done only when
  changing to a different user address environment.

Another issue is when a new process is created; the address environment
of the new process must be temporarily instantiated by up_addrenv_select().
However, the system scheduler does not know that the process has a different
address environment to its own and when / if a context restore happens, the
wrong MMU page directory is restored and the process will either crash or
do something horribly wrong.

The following changes are needed to fix the issues:
- Add mm_curr which is the current address environment of the process
- Add a reference counter to safeguard the address environment
- Whenever an address environment is mapped to MMU, its reference counter
  is incremented
- Whenever and address environment is unmapped from MMU, its reference
  counter is decremented, and tested. If no more references -> drop the
  address environment and release the memory as well
- To limit the context switch delay, the address environment is freed in
  a separate low priority clean-up thread (LPWORK)
- When a process temporarily instantiates another process's address
  environment, the scheduler will now know of this and will restore the
  correct mappings to MMU

Why is this not causing more noticeable issues ? The problem only happens
under the aforementioned special conditions, and if a context switch or
IRQ occurs during this time.
2023-02-08 02:51:23 +08:00
..
configs sched/addrenv: Fix system crash when process group has been deleted 2023-02-08 02:51:23 +08:00
include arch: Change the linker generated symbols from uint32_t to uint8_t * 2022-09-24 21:26:56 +02:00
scripts risc-v/qemu-rv: Mark the page table section as NOLOAD 2022-12-08 21:56:03 +08:00
src boards/sim: support rc.sysinit 2022-04-21 12:54:53 +03:00
Kconfig
README.txt boards: rv-virt: Add virtio-net to netnsh/netnsh_smp/netnsh64 2022-11-29 13:16:44 +08:00

README.txt 

1. Download and install toolchain

  $ curl https://static.dev.sifive.com/dev-tools/riscv64-unknown-elf-gcc-8.3.0-2019.08.0-x86_64-linux-ubuntu14.tar.gz

2. Build and install qemu

  $ git clone https://github.com/qemu/qemu
  $ cd qemu
  $ ./configure --target-list=riscv32-softmmu,riscv64-softmmu
  $ make
  $ sudo make install

3.1. Configure and build NuttX for BUILD_FLAT

  $ mkdir ./nuttx; cd ./nuttx
  $ git clone https://github.com/apache/nuttx.git nuttx
  $ git clone https://github.com/apache/nuttx-apps.git apps
  $ cd nuttx
  $ make distclean
  $ ./tools/configure.sh rv-virt:nsh
  $ make V=1 -j7

3.2 Configure and build NuttX for BUILD_KERNEL

  $ mkdir ./nuttx; cd ./nuttx
  $ git clone https://github.com/apache/nuttx.git nuttx
  $ git clone https://github.com/apache/nuttx-apps.git apps
  $ cd nuttx
  $ make distclean
  $ ./tools/configure.sh rv-virt:knsh64
  $ make V=1 -j7
  $ make export V=1
  $ cd ../apps
  $ ./tools/mkimport.sh -z -x ../nuttx/nuttx-export-*.tar.gz
  $ make import V=1
  $ cd ../nuttx

4. Run the nuttx with qemu

  $ qemu-system-riscv32 -semihosting -M virt,aclint=on -cpu rv32 -smp 8 -bios none -kernel nuttx -nographic

  or

  $ qemu-system-riscv64 -semihosting -M virt,aclint=on -cpu rv64 -smp 8 -bios none -kernel nuttx -nographic

  NuttShell (NSH) NuttX-10.3.0-RC1
  nsh> mount -t hostfs -o fs=. /host
  nsh> cat /host/AUTHORS
  This is a list of all the contributors that have submitted ICLA, SGA
  If you are not on this list and believe you should be, please inform us.

  ICLA
  ====
  ...
  nsh>

4. Run the nuttx network with qemu

  $ qemu-system-riscv32 -semihosting -M virt,aclint=on -cpu rv32 -smp 8 \
  -global virtio-mmio.force-legacy=false \
  -netdev user,id=u1,hostfwd=tcp:127.0.0.1:10023-10.0.2.15:23,hostfwd=tcp:127.0.0.1:15001-10.0.2.15:5001 \
  -device virtio-net-device,netdev=u1,bus=virtio-mmio-bus.0 \
  -bios none -kernel nuttx -nographic

  or

  $ qemu-system-riscv64 -semihosting -M virt,aclint=on -cpu rv64 -smp 8 \
  -global virtio-mmio.force-legacy=false \
  -netdev user,id=u1,hostfwd=tcp:127.0.0.1:10023-10.0.2.15:23,hostfwd=tcp:127.0.0.1:15001-10.0.2.15:5001 \
  -device virtio-net-device,netdev=u1,bus=virtio-mmio-bus.0 \
  -bios none -kernel nuttx -nographic

5. TODO

  Support FPU
  Support RISC-V User mode