On 10/14/2013 11:39 PM, Will Deacon wrote:
> On Mon, Oct 14, 2013 at 04:30:00PM +0100, Jiang Liu wrote:
>> On 10/14/2013 11:16 PM, Will Deacon wrote:
>>> On Sun, Oct 13, 2013 at 03:20:18PM +0100, Jiang Liu wrote:
>>>> From: Jiang Liu <jiang....@huawei.com>
>>>>
>>>> Restore FPSIMD control and status registers to default values
>>>> when creating new FPSIMD contexts for kernel context and reset
>>>> FPSIMD status register when creating FPSIMD context for signal
>>>> handling, otherwise the stale value in FPSIMD control and status
>>>> registers may affect the new kernal or signal handling contexts.
>>>>
>>>> Signed-off-by: Jiang Liu <jiang....@huawei.com>
>>>> Cc: Jiang Liu <liu...@gmail.com>
>>>> ---
>>>> arch/arm64/include/asm/fpsimd.h | 16 ++++++++++++++++
>>>> arch/arm64/kernel/fpsimd.c | 11 +++++++++--
>>>> arch/arm64/kernel/signal.c | 1 +
>>>> arch/arm64/kernel/signal32.c | 1 +
>>>> 4 files changed, 27 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/arch/arm64/include/asm/fpsimd.h
>>>> b/arch/arm64/include/asm/fpsimd.h
>>>> index c43b4ac..b2dc30f 100644
>>>> --- a/arch/arm64/include/asm/fpsimd.h
>>>> +++ b/arch/arm64/include/asm/fpsimd.h
>>>> @@ -50,8 +50,24 @@ struct fpsimd_state {
>>>> #define VFP_STATE_SIZE ((32 * 8) + 4)
>>>> #endif
>>>>
>>>> +#define AARCH64_FPCR_DEFAULT_VAL 0
>>>> +
>>>> struct task_struct;
>>>>
>>>> +static inline void fpsimd_init_hw_state(void)
>>>> +{
>>>> + int val = AARCH64_FPCR_DEFAULT_VAL;
>>>> +
>>>> + asm ("msr fpcr, %x0\n"
>>>> + "msr fpsr, xzr\n"
>>>> + : : "r"(val));
>>>> +}
>>>> +
>>>> +static inline void fpsimd_clear_fpsr(void)
>>>> +{
>>>> + asm ("msr fpsr, xzr\n");
>>>> +}
>>>
>>> You have pretty weak asm constraints here...
>> Hi Will,
>> We will add an explicit "volatile" here. But according to GCC docs, it
>> should have the same effect:
>> An asm instruction without any output operands is treated identically to
>> a volatile asm instruction.
>
> I don't think volatile is enough to prevent re-ordering across a function
> call; it just prevents the block from being optimised away entirely and/or
> reordered with respect to other volatile statements.
>
> A "memory" clobber should do the trick in this case.
Thanks for education, will fix it in next version.
>
> Will
>
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