[0/2] riscv: Correct the initialized flow of FP and __fstate_clean()

Message

Vincent Chen Aug. 8, 2019, 7:58 a.m. UTC

The following two reasons cause FP registers are sometimes not
initialized before starting the user program.
1. Currently, the FP context is initialized in flush_thread() function
   and we expect these initial values to be restored to FP register when
   doing FP context switch. However, the FP context switch only occurs in
   switch_to function. Hence, if this process does not be scheduled out
   and scheduled in before entering the user space, the FP registers
   have no chance to initialize.
2. In flush_thread(), the state of reg->sstatus.FS inherits from the
   parent. Hence, the state of reg->sstatus.FS may be dirty. If this
   process is scheduled out during flush_thread() and initializing the
   FP register, the fstate_save() in switch_to will corrupt the FP context
   which has been initialized until flush_thread().
In addition, the __fstate_clean() function cannot correctly set the state
of sstatus.FS to SR_FS_CLEAN. These problems will be solved in this patch
set.


Vincent Chen (2):
  riscv: Correct the initialized flow of FP register
  riscv: Make __fstate_clean() can work correctly.

 arch/riscv/include/asm/switch_to.h |  8 +++++++-
 arch/riscv/kernel/process.c        | 13 +++++++++++--
 2 files changed, 18 insertions(+), 3 deletions(-)