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    • Marcos Paulo de Souza's avatar
      selftests: livepatch: Test livepatching a heavily called syscall · 6a717704
      Marcos Paulo de Souza authored
      The test proves that a syscall can be livepatched. It is interesting
      because syscalls are called a tricky way. Also the process gets
      livepatched either when sleeping in the userspace or when entering
      or leaving the kernel space.
      
      The livepatch is a bit tricky:
        1. The syscall function name is architecture specific. Also
           ARCH_HAS_SYSCALL_WRAPPER must be taken in account.
      
        2. The syscall must stay working the same way for other processes
           on the system. It is solved by decrementing a counter only
           for PIDs of the test processes. It means that the test processes
           has to call the livepatched syscall at least once.
      
      The test creates one userspace process per online cpu. The processes
      are calling getpid in a busy loop. The intention is to create random
      locations when the livepatch gets enabled. Nothing is guarantted.
      The magic is in the randomness.
      Reviewed-by: default avatarJoe Lawrence <joe.lawrence@redhat.com>
      Reviewed-by: default avatarPetr Mladek <pmladek@suse.com>
      Signed-off-by: default avatarMarcos Paulo de Souza <mpdesouza@suse.com>
      Signed-off-by: default avatarShuah Khan <skhan@linuxfoundation.org>
      6a717704