[RFC v3 PATCH 4/7] ARM64: add support for kernel mode NEON in atomic context
Ard Biesheuvel
ard.biesheuvel at linaro.org
Sun Oct 13 08:15:00 EDT 2013
This patch modifies kernel_neon_begin() and kernel_neon_end(), so
they may be called from any context. To address the in_interrupt()
case, they now both take a parameter defined by DEFINE_NEON_REGSTACK()
or DEFINE_NEON_REGSTACK_PARTIAL() [in case only a few NEON registers
are in fact used]. The !in_interrupt() case is unchanged from before.
Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
---
arch/arm64/include/asm/fpsimd.h | 17 +++++++++++++++++
arch/arm64/include/asm/fpsimdmacros.h | 35 +++++++++++++++++++++++++++++++++++
arch/arm64/include/asm/neon.h | 31 +++++++++++++++++++++++++++++--
arch/arm64/kernel/entry-fpsimd.S | 24 ++++++++++++++++++++++++
arch/arm64/kernel/fpsimd.c | 29 ++++++++++++++++++-----------
5 files changed, 123 insertions(+), 13 deletions(-)
diff --git a/arch/arm64/include/asm/fpsimd.h b/arch/arm64/include/asm/fpsimd.h
index c43b4ac..755bdf1 100644
--- a/arch/arm64/include/asm/fpsimd.h
+++ b/arch/arm64/include/asm/fpsimd.h
@@ -39,6 +39,18 @@ struct fpsimd_state {
};
};
+/*
+ * Variable sized struct for stacking the bottom 'n' FP/SIMD registers.
+ * Mainly intended for kernel use of v8 Crypto Extensions which only
+ * needs a few registers and may need to execute in atomic context.
+ */
+struct fpsimd_partial_state {
+ u32 fpsr;
+ u32 fpcr;
+ __uint128_t vregs[] __aligned(16);
+} __aligned(16);
+
+
#if defined(__KERNEL__) && defined(CONFIG_COMPAT)
/* Masks for extracting the FPSR and FPCR from the FPSCR */
#define VFP_FPSCR_STAT_MASK 0xf800009f
@@ -55,6 +67,11 @@ struct task_struct;
extern void fpsimd_save_state(struct fpsimd_state *state);
extern void fpsimd_load_state(struct fpsimd_state *state);
+extern void fpsimd_save_partial_state(struct fpsimd_partial_state *state,
+ u32 num_regs);
+extern void fpsimd_load_partial_state(struct fpsimd_partial_state *state,
+ u32 num_regs);
+
extern void fpsimd_thread_switch(struct task_struct *next);
extern void fpsimd_flush_thread(void);
diff --git a/arch/arm64/include/asm/fpsimdmacros.h b/arch/arm64/include/asm/fpsimdmacros.h
index bbec599..f771b69 100644
--- a/arch/arm64/include/asm/fpsimdmacros.h
+++ b/arch/arm64/include/asm/fpsimdmacros.h
@@ -62,3 +62,38 @@
ldr w\tmpnr, [\state, #16 * 2 + 4]
msr fpcr, x\tmpnr
.endm
+
+.altmacro
+.macro q2op, op, q1, q2, state
+ \op q\q1, q\q2, [\state, #-(16 * \q1) - 16]
+.endm
+
+.macro fpsimd_save_partial state, num, tmpnr1, tmpnr2
+ mrs x\tmpnr1, fpsr
+ mrs x\tmpnr2, fpcr
+ stp w\tmpnr1, w\tmpnr2, [\state]
+ adr x\tmpnr1, 0f
+ add \state, \state, \num, lsl #4
+ sub x\tmpnr1, x\tmpnr1, \num, lsl #1
+ br x\tmpnr1
+ .irp qa, 30, 28, 26, 24, 22, 20, 18, 16, 14, 12, 10, 8, 6, 4, 2, 0
+ qb = \qa + 1
+ q2op stp, \qa, %qb, \state
+ .endr
+0:
+.endm
+
+.macro fpsimd_restore_partial state, num, tmpnr1, tmpnr2
+ ldp w\tmpnr1, w\tmpnr2, [\state]
+ msr fpsr, x\tmpnr1
+ msr fpcr, x\tmpnr2
+ adr x\tmpnr1, 0f
+ add \state, \state, \num, lsl #4
+ sub x\tmpnr1, x\tmpnr1, \num, lsl #1
+ br x\tmpnr1
+ .irp qa, 30, 28, 26, 24, 22, 20, 18, 16, 14, 12, 10, 8, 6, 4, 2, 0
+ qb = \qa + 1
+ q2op ldp, \qa, %qb, \state
+ .endr
+0:
+.endm
diff --git a/arch/arm64/include/asm/neon.h b/arch/arm64/include/asm/neon.h
index b0cc58a9..e496dce 100644
--- a/arch/arm64/include/asm/neon.h
+++ b/arch/arm64/include/asm/neon.h
@@ -8,7 +8,34 @@
* published by the Free Software Foundation.
*/
+#include <linux/hardirq.h>
+#include <linux/types.h>
+#include <asm/fpsimd.h>
+
#define cpu_has_neon() (1)
-void kernel_neon_begin(void);
-void kernel_neon_end(void);
+/*
+ * Avoid wasting stack space by making the size of the allocated area depend on
+ * whether we are currently running in process context. (If this is the case, we
+ * will use the normal preserve/restore mechanism, leaving the allocated stack
+ * space unused.)
+ */
+#define __VREG_SIZE(num) \
+ ((!in_interrupt()) ? 0 : (num) > 32 ? 512 : 32 * (((num) + 1) & ~1U))
+
+#define DEFINE_NEON_REGSTACK_PARTIAL(v, num) \
+ struct { \
+ struct fpsimd_partial_state regs; \
+ u8 vregs[__VREG_SIZE(num)]; \
+ } v
+
+#define DEFINE_NEON_REGSTACK(name) DEFINE_NEON_REGSTACK_PARTIAL(name, 32)
+
+#define kernel_neon_begin(p) \
+ __kernel_neon_begin(&(p).regs, sizeof((p).vregs)/16)
+
+#define kernel_neon_end(p) \
+ __kernel_neon_end(&(p).regs, sizeof((p).vregs)/16)
+
+void __kernel_neon_begin(struct fpsimd_partial_state *regs, u32 num_regs);
+void __kernel_neon_end(struct fpsimd_partial_state *regs, u32 num_regs);
diff --git a/arch/arm64/kernel/entry-fpsimd.S b/arch/arm64/kernel/entry-fpsimd.S
index 6a27cd6..aa73ee9 100644
--- a/arch/arm64/kernel/entry-fpsimd.S
+++ b/arch/arm64/kernel/entry-fpsimd.S
@@ -41,3 +41,27 @@ ENTRY(fpsimd_load_state)
fpsimd_restore x0, 8
ret
ENDPROC(fpsimd_load_state)
+
+#ifdef CONFIG_KERNEL_MODE_NEON
+
+/*
+ * Save the bottom n FP registers.
+ *
+ * x0 - pointer to struct fpsimd_partial_state
+ */
+ENTRY(fpsimd_save_partial_state)
+ fpsimd_save_partial x0, x1, 8, 9
+ ret
+ENDPROC(fpsimd_load_partial_state)
+
+/*
+ * Load the bottom n FP registers.
+ *
+ * x0 - pointer to struct fpsimd_partial_state
+ */
+ENTRY(fpsimd_load_partial_state)
+ fpsimd_restore_partial x0, x1, 8, 9
+ ret
+ENDPROC(fpsimd_load_partial_state)
+
+#endif
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index a52affd..34fa94b 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -89,22 +89,29 @@ void fpsimd_flush_thread(void)
/*
* Kernel-side NEON support functions
*/
-void kernel_neon_begin(void)
+void __kernel_neon_begin(struct fpsimd_partial_state *regs, u32 num_regs)
{
- /* Avoid using the NEON in interrupt context */
- BUG_ON(in_interrupt());
- preempt_disable();
-
- if (current->mm && !test_and_set_thread_flag(TIF_RELOAD_FPSTATE))
- fpsimd_save_state(¤t->thread.fpsimd_state);
+ if (in_interrupt()) {
+ BUG_ON(!num_regs);
+ fpsimd_save_partial_state(regs, num_regs);
+ } else {
+ preempt_disable();
+ if (current->mm &&
+ !test_and_set_thread_flag(TIF_RELOAD_FPSTATE))
+ fpsimd_save_state(¤t->thread.fpsimd_state);
+ }
}
-EXPORT_SYMBOL(kernel_neon_begin);
+EXPORT_SYMBOL(__kernel_neon_begin);
-void kernel_neon_end(void)
+void __kernel_neon_end(struct fpsimd_partial_state *regs, u32 num_regs)
{
- preempt_enable();
+ if (in_interrupt()) {
+ BUG_ON(!num_regs);
+ fpsimd_load_partial_state(regs, num_regs);
+ } else
+ preempt_enable();
}
-EXPORT_SYMBOL(kernel_neon_end);
+EXPORT_SYMBOL(__kernel_neon_end);
#endif /* CONFIG_KERNEL_MODE_NEON */
--
1.8.1.2
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