x86/fpu: Split an fpstate_alloc_init() function out of init_fpu()

Most init_fpu() users don't want the register-saving aspect of the
function, they are calling it for 'current' and when FPU registers
are not allocated and initialized yet.

Split out a simplified API that does just that (and add debug-checks
for these conditions): fpstate_alloc_init().

Use it where appropriate.

Reviewed-by: Borislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 31 insertions, 0 deletions

diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
index 29251f5668b1..56b6e726fb60 100644
--- a/arch/x86/kernel/i387.c
+++ b/arch/x86/kernel/i387.c
@@ -247,6 +247,37 @@ void fpu_finit(struct fpu *fpu)
 EXPORT_SYMBOL_GPL(fpu_finit);
 
 /*
+ * Allocate the backing store for the current task's FPU registers
+ * and initialize the registers themselves as well.
+ *
+ * Can fail.
+ */
+int fpstate_alloc_init(struct task_struct *curr)
+{
+	int ret;
+
+	if (WARN_ON_ONCE(curr != current))
+		return -EINVAL;
+	if (WARN_ON_ONCE(curr->flags & PF_USED_MATH))
+		return -EINVAL;
+
+	/*
+	 * Memory allocation at the first usage of the FPU and other state.
+	 */
+	ret = fpu_alloc(&curr->thread.fpu);
+	if (ret)
+		return ret;
+
+	fpu_finit(&curr->thread.fpu);
+
+	/* Safe to do for the current task: */
+	curr->flags |= PF_USED_MATH;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(fpstate_alloc_init);
+
+/*
  * The _current_ task is using the FPU for the first time
  * so initialize it and set the mxcsr to its default
  * value at reset if we support XMM instructions and then