On 09/27/2013 07:35 PM, Catalin Marinas wrote:

On Fri, Sep 27, 2013 at 09:04:42AM +0100, Jiang Liu wrote:

quoted

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index bb785d2..12a25e5 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c

@@ -80,9 +80,14 @@ void fpsimd_thread_switch(struct task_struct *next)
 
 void fpsimd_flush_thread(void)
 {
+	struct fpsimd_state *state = &current->thread.fpsimd_state;
+
 	preempt_disable();
-	memset(&current->thread.fpsimd_state, 0, sizeof(struct fpsimd_state));
-	fpsimd_load_state(&current->thread.fpsimd_state);
+	memset(state, 0, sizeof(struct fpsimd_state));
+#if (AARCH64_FPCR_DEFAULT_VAL != 0)
+	state->fpcr = AARCH64_FPCR_DEFAULT_VAL;
+#endif
+	fpsimd_load_state(state);
 	preempt_enable();

We can leave this to 0 as the default for user. Glibc already programs
this register.

OK, will drop it.

quoted

 }
 

@@ -99,6 +104,8 @@ void kernel_neon_begin(void)
 
 	if (current->mm)
 		fpsimd_save_state(&current->thread.fpsimd_state);
+
+	fpsimd_init_hw_state();

This function should indeed do some initialisation rather than relying
on whatever the user set for FPCR.

quoted

diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index 890a591..6d80612 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c

@@ -52,6 +52,7 @@ static int preserve_fpsimd_context(struct fpsimd_context __user *ctx)
 
 	/* dump the hardware registers to the fpsimd_state structure */
 	fpsimd_save_state(fpsimd);
+	fpsimd_init_hw_state();

Here I think we need to leave the default user setting for fpcr as
decided by glibc (or libgcc) when an application starts.

OK, will keep FPCR and clear FPSR.

quoted

 	/* copy the FP and status/control registers */
 	err = __copy_to_user(ctx->vregs, fpsimd->vregs, sizeof(fpsimd->vregs));

diff --git a/arch/arm64/kernel/signal32.c b/arch/arm64/kernel/signal32.c
index e393174..cb2cb41 100644
--- a/arch/arm64/kernel/signal32.c
+++ b/arch/arm64/kernel/signal32.c

@@ -248,6 +248,7 @@ static int compat_preserve_vfp_context(struct compat_vfp_sigframe __user *frame)
 	 * in AArch32.
 	 */
 	fpsimd_save_state(fpsimd);
+	fpsimd_init_hw_state();

Same here.