diff options
author | Paul Burton <paul.burton@mips.com> | 2018-11-07 23:14:00 +0000 |
---|---|---|
committer | Paul Burton <paul.burton@mips.com> | 2018-11-09 10:23:14 -0800 |
commit | 1975ed43ce67542befed188f6aed6a82cfaffd0b (patch) | |
tree | 05a793e45dad2239c041495da54d2db361c52fc3 /arch/mips/kernel/unaligned.c | |
parent | cc97ab235f3fe32401ca198cebe6f42642e95770 (diff) |
MIPS: Ensure emulated FP sets PF_USED_MATH
Emulated floating point instructions don't ensure that the PF_USED_MATH
flag is set for the task. This results in a couple of inconsistencies:
- ptrace will return the default initial state of FP registers rather
than the values actually stored in struct thread_struct, hiding
state that has been updated by emulated floating point instructions.
- If a task migrates to a CPU with an FPU after having emulated
floating point instructions then its floating point register state
will be reset to the default ~0 bit pattern, losing state from the
emulated instructions.
Fix this by calling init_fp_ctx() from fpu_emulator_cop1Handler() to
consistently initialize FP state if it was previously uninitialized,
setting the PF_USED_MATH flag in the process.
All callers of fpu_emulator_cop1Handler() either call lose_fpu(1) before
it in order to save any live FPU registers to struct thread_struct, or
in the case of do_cpu() already know that the task does not own an FPU
so lose_fpu(1) would be a no-op. Since we know that saving FP context
will be unnecessary in the case where FP context was just initialized we
move this call into fpu_emulator_cop1Handler() too, providing
consistency & avoiding needless duplication.
Calls to own_fpu(1) are common after return from
fpu_emulator_cop1Handler() too, but this would not be a no-op in the
do_cpu() case so these are left as-is. A potential future improvement
could be to have fpu_emulator_cop1Handler() restore FPU state
automatically only if it saved it, though this may not be optimal if
some callers are better off without their current calls to own_fpu(1).
One potential example of this could be mipsr2_decoder() which as-is
could end up saving & restoring FP context repeatedly & unnecessarily if
emulating multiple FP instructions.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/21003/
Cc: linux-mips@linux-mips.org
Diffstat (limited to 'arch/mips/kernel/unaligned.c')
-rw-r--r-- | arch/mips/kernel/unaligned.c | 2 |
1 files changed, 0 insertions, 2 deletions
diff --git a/arch/mips/kernel/unaligned.c b/arch/mips/kernel/unaligned.c index ce446eed62d2..4c7de9f6373d 100644 --- a/arch/mips/kernel/unaligned.c +++ b/arch/mips/kernel/unaligned.c @@ -1220,7 +1220,6 @@ static void emulate_load_store_insn(struct pt_regs *regs, die_if_kernel("Unaligned FP access in kernel code", regs); BUG_ON(!used_math()); - lose_fpu(1); /* Save FPU state for the emulator. */ res = fpu_emulator_cop1Handler(regs, ¤t->thread.fpu, 1, &fault_addr); own_fpu(1); /* Restore FPU state. */ @@ -1733,7 +1732,6 @@ fpu_emul: BUG_ON(!used_math()); BUG_ON(!is_fpu_owner()); - lose_fpu(1); /* save the FPU state for the emulator */ res = fpu_emulator_cop1Handler(regs, ¤t->thread.fpu, 1, &fault_addr); own_fpu(1); /* restore FPU state */ |