arm64: add abstractions for FPSIMD state manipulation

There are two tacit assumptions in the FPSIMD handling code that will no longer
hold after the next patch that optimizes away some FPSIMD state restores:
. the FPSIMD registers of this CPU contain the userland FPSIMD state of
  task 'current';
. when switching to a task, its FPSIMD state will always be restored from
  memory.

This patch adds the following functions to abstract away from straight FPSIMD
register file saves and restores:
- fpsimd_preserve_current_state -> ensure current's FPSIMD state is saved
- fpsimd_update_current_state -> replace current's FPSIMD state

Where necessary, the signal handling and fork code are updated to use the above
wrappers instead of poking into the FPSIMD registers directly.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

diff --git a/arch/arm64/include/asm/fpsimd.h b/arch/arm64/include/asm/fpsimd.h
index c43b4ac13008ffec8f0b39101e5cfd77e43fd3b5..f4e524b67e912296ef7c539e535987b1f3405322 100644 (file)
--- a/arch/arm64/include/asm/fpsimd.h
+++ b/arch/arm64/include/asm/fpsimd.h
@@ -58,6 +58,9 @@ extern void fpsimd_load_state(struct fpsimd_state *state);
 extern void fpsimd_thread_switch(struct task_struct *next);
 extern void fpsimd_flush_thread(void);
 
+extern void fpsimd_preserve_current_state(void);
+extern void fpsimd_update_current_state(struct fpsimd_state *state);
+
 #endif
 
 #endif

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 4aef42a04bdcc38baa84c2090ffc537d67770854..8a97163debc77e9e9c0d7aaf7bfbda0ec6e392fe 100644 (file)
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -87,6 +87,26 @@ void fpsimd_flush_thread(void)
        preempt_enable();
 }
 
+/*
+ * Save the userland FPSIMD state of 'current' to memory
+ */
+void fpsimd_preserve_current_state(void)
+{
+       preempt_disable();
+       fpsimd_save_state(&current->thread.fpsimd_state);
+       preempt_enable();
+}
+
+/*
+ * Load an updated userland FPSIMD state for 'current' from memory
+ */
+void fpsimd_update_current_state(struct fpsimd_state *state)
+{
+       preempt_disable();
+       fpsimd_load_state(state);
+       preempt_enable();
+}
+
 #ifdef CONFIG_KERNEL_MODE_NEON
 
 /*

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 6391485f342daaac57e207f129a62e28d169b114..c5693163408c3bb9ab967dc7819ee9ae14282c0d 100644 (file)
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -205,7 +205,7 @@ void release_thread(struct task_struct *dead_task)
 
 int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
 {
-       fpsimd_save_state(&current->thread.fpsimd_state);
+       fpsimd_preserve_current_state();
        *dst = *src;
        return 0;
 }

diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index 890a591f75dd1848e28e1ea62413775be5394c6d..06448a77ff5351a18ad98409311675144453462a 100644 (file)
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -51,7 +51,7 @@ static int preserve_fpsimd_context(struct fpsimd_context __user *ctx)
        int err;
 
        /* dump the hardware registers to the fpsimd_state structure */
-       fpsimd_save_state(fpsimd);
+       fpsimd_preserve_current_state();
 
        /* copy the FP and status/control registers */
        err = __copy_to_user(ctx->vregs, fpsimd->vregs, sizeof(fpsimd->vregs));
@@ -86,11 +86,8 @@ static int restore_fpsimd_context(struct fpsimd_context __user *ctx)
        __get_user_error(fpsimd.fpcr, &ctx->fpcr, err);
 
        /* load the hardware registers from the fpsimd_state structure */
-       if (!err) {
-               preempt_disable();
-               fpsimd_load_state(&fpsimd);
-               preempt_enable();
-       }
+       if (!err)
+               fpsimd_update_current_state(&fpsimd);
 
        return err ? -EFAULT : 0;
 }

diff --git a/arch/arm64/kernel/signal32.c b/arch/arm64/kernel/signal32.c
index b3fc9f5ec6d34b423d70bc5f0fd75836fc307c95..ac7e237d0bda50aa9bb426509fc5689acbecfce0 100644 (file)
--- a/arch/arm64/kernel/signal32.c
+++ b/arch/arm64/kernel/signal32.c
@@ -219,7 +219,7 @@ static int compat_preserve_vfp_context(struct compat_vfp_sigframe __user *frame)
         * Note that this also saves V16-31, which aren't visible
         * in AArch32.
         */
-       fpsimd_save_state(fpsimd);
+       fpsimd_preserve_current_state();
 
        /* Place structure header on the stack */
        __put_user_error(magic, &frame->magic, err);
@@ -282,11 +282,8 @@ static int compat_restore_vfp_context(struct compat_vfp_sigframe __user *frame)
         * We don't need to touch the exception register, so
         * reload the hardware state.
         */
-       if (!err) {
-               preempt_disable();
-               fpsimd_load_state(&fpsimd);
-               preempt_enable();
-       }
+       if (!err)
+               fpsimd_update_current_state(&fpsimd);
 
        return err ? -EFAULT : 0;
 }