s390/fpu: decrease stack usage for some cases

The kernel_fpu structure has a quite large size of 520 bytes. In order to
reduce stack footprint introduce several kernel fpu structures with
different and also smaller sizes. This way every kernel fpu user must use
the correct variant. A compile time check verifies that the correct variant
is used.

There are several users which use only 16 instead of all 32 vector
registers. For those users the new kernel_fpu_16 structure with a size of
only 266 bytes can be used.

Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

1 files changed, 42 insertions, 6 deletions

diff --git a/arch/s390/include/asm/fpu.h b/arch/s390/include/asm/fpu.h
index e706af26c5d0..c1b3920092a1 100644
--- a/arch/s390/include/asm/fpu.h
+++ b/arch/s390/include/asm/fpu.h
@@ -162,28 +162,64 @@ static __always_inline void load_fp_regs_vx(__vector128 *vxrs)
 	__load_fp_regs(fprs, sizeof(__vector128) / sizeof(freg_t));
 }
 
-static inline void kernel_fpu_begin(struct kernel_fpu *state, int flags)
+static inline void _kernel_fpu_begin(struct kernel_fpu *state, int flags)
 {
-	state->mask = READ_ONCE(current->thread.kfpu_flags);
+	state->hdr.mask = READ_ONCE(current->thread.kfpu_flags);
 	if (!test_thread_flag(TIF_FPU)) {
 		/* Save user space FPU state and register contents */
 		save_user_fpu_regs();
-	} else if (state->mask & flags) {
+	} else if (state->hdr.mask & flags) {
 		/* Save FPU/vector register in-use by the kernel */
 		__kernel_fpu_begin(state, flags);
 	}
 	__atomic_or(flags, &current->thread.kfpu_flags);
 }
 
-static inline void kernel_fpu_end(struct kernel_fpu *state, int flags)
+static inline void _kernel_fpu_end(struct kernel_fpu *state, int flags)
 {
-	WRITE_ONCE(current->thread.kfpu_flags, state->mask);
-	if (state->mask & flags) {
+	WRITE_ONCE(current->thread.kfpu_flags, state->hdr.mask);
+	if (state->hdr.mask & flags) {
 		/* Restore FPU/vector register in-use by the kernel */
 		__kernel_fpu_end(state, flags);
 	}
 }
 
+void __kernel_fpu_invalid_size(void);
+
+static __always_inline void kernel_fpu_check_size(int flags, unsigned int size)
+{
+	unsigned int cnt = 0;
+
+	if (flags & KERNEL_VXR_V0V7)
+		cnt += 8;
+	if (flags & KERNEL_VXR_V8V15)
+		cnt += 8;
+	if (flags & KERNEL_VXR_V16V23)
+		cnt += 8;
+	if (flags & KERNEL_VXR_V24V31)
+		cnt += 8;
+	if (cnt != size)
+		__kernel_fpu_invalid_size();
+}
+
+#define kernel_fpu_begin(state, flags)					\
+{									\
+	typeof(state) s = (state);					\
+	int _flags = (flags);						\
+									\
+	kernel_fpu_check_size(_flags, ARRAY_SIZE(s->vxrs));		\
+	_kernel_fpu_begin((struct kernel_fpu *)s, _flags);		\
+}
+
+#define kernel_fpu_end(state, flags)					\
+{									\
+	typeof(state) s = (state);					\
+	int _flags = (flags);						\
+									\
+	kernel_fpu_check_size(_flags, ARRAY_SIZE(s->vxrs));		\
+	_kernel_fpu_end((struct kernel_fpu *)s, _flags);		\
+}
+
 static inline void save_kernel_fpu_regs(struct thread_struct *thread)
 {
 	struct fpu *state = &thread->kfpu;