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.
Will
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