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s390/fpu: improve kernel_fpu_[begin|end]

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In case of nested user of the FPU or vector registers in the kernel
the current code uses the mask of the FPU/vector registers of the
previous contexts to decide which registers to save and restore.
E.g. if the previous context used KERNEL_VXR_V0V7 and the next
context wants to use KERNEL_VXR_V24V31 the first 8 vector registers
are stored to the FPU state structure. But this is not necessary
as the next context does not use these registers.

Rework the FPU/vector register save and restore code. The new code
does a few things differently:
1) A lowcore field is used instead of a per-cpu variable.
2) The kernel_fpu_end function now has two parameters just like
   kernel_fpu_begin. The register flags are required by both
   functions to save / restore the minimal register set.
3) The inline functions kernel_fpu_begin/kernel_fpu_end now do the
   update of the register masks. If the user space FPU registers
   have already been stored neither save_fpu_regs nor the
   __kernel_fpu_begin/__kernel_fpu_end functions have to be called
   for the first context. In this case kernel_fpu_begin adds 7
   instructions and kernel_fpu_end adds 4 instructions.
3) The inline assemblies in __kernel_fpu_begin / __kernel_fpu_end
   to save / restore the vector registers are simplified a bit.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Martin Schwidefsky
2016-08-22 12:06:21 +02:00
parent 0eab11c7e0
commit 7f79695cc1
5 changed files with 148 additions and 210 deletions
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32
arch/s390/include/asm/fpu/api.h
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@@ -64,18 +64,18 @@ static inline int test_fp_ctl(u32 fpc)
return rc;
}
#define KERNEL_VXR_V0V7 1
#define KERNEL_VXR_V8V15 2
#define KERNEL_VXR_V16V23 4
#define KERNEL_VXR_V24V31 8
#define KERNEL_FPR 16
#define KERNEL_FPC 256
#define KERNEL_FPC 1
#define KERNEL_VXR_V0V7 2
#define KERNEL_VXR_V8V15 4
#define KERNEL_VXR_V16V23 8
#define KERNEL_VXR_V24V31 16
#define KERNEL_VXR_LOW (KERNEL_VXR_V0V7|KERNEL_VXR_V8V15)
#define KERNEL_VXR_MID (KERNEL_VXR_V8V15|KERNEL_VXR_V16V23)
#define KERNEL_VXR_HIGH (KERNEL_VXR_V16V23|KERNEL_VXR_V24V31)
#define KERNEL_FPU_MASK (KERNEL_VXR_LOW|KERNEL_VXR_HIGH|KERNEL_FPR)
#define KERNEL_VXR (KERNEL_VXR_LOW|KERNEL_VXR_HIGH)
#define KERNEL_FPR (KERNEL_FPC|KERNEL_VXR_V0V7)
struct kernel_fpu;
@@ -87,18 +87,28 @@ struct kernel_fpu;
* Prefer using the kernel_fpu_begin()/kernel_fpu_end() pair of functions.
*/
void __kernel_fpu_begin(struct kernel_fpu *state, u32 flags);
void __kernel_fpu_end(struct kernel_fpu *state);
void __kernel_fpu_end(struct kernel_fpu *state, u32 flags);
static inline void kernel_fpu_begin(struct kernel_fpu *state, u32 flags)
{
preempt_disable();
__kernel_fpu_begin(state, flags);
state->mask = S390_lowcore.fpu_flags;
if (!test_cpu_flag(CIF_FPU))
/* Save user space FPU state and register contents */
save_fpu_regs();
else if (state->mask & flags)
/* Save FPU/vector register in-use by the kernel */
__kernel_fpu_begin(state, flags);
S390_lowcore.fpu_flags |= flags;
}
static inline void kernel_fpu_end(struct kernel_fpu *state)
static inline void kernel_fpu_end(struct kernel_fpu *state, u32 flags)
{
__kernel_fpu_end(state);
S390_lowcore.fpu_flags = state->mask;
if (state->mask & flags)
/* Restore FPU/vector register in-use by the kernel */
__kernel_fpu_end(state, flags);
preempt_enable();
}