x86/fpu: Split out the boot time FPU init code into fpu/init.c

Move boot time FPU initialization code into init.c, to better
isolate it into its own domain.

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, 93 insertions, 0 deletions

diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
new file mode 100644
index 000000000000..0a666298abbd
--- /dev/null
+++ b/arch/x86/kernel/fpu/init.c
@@ -0,0 +1,93 @@
+/*
+ * x86 FPU boot time init code
+ */
+#include <asm/fpu-internal.h>
+#include <asm/tlbflush.h>
+
+unsigned int mxcsr_feature_mask __read_mostly = 0xffffffffu;
+unsigned int xstate_size;
+EXPORT_SYMBOL_GPL(xstate_size);
+static struct i387_fxsave_struct fx_scratch;
+
+static void mxcsr_feature_mask_init(void)
+{
+	unsigned long mask = 0;
+
+	if (cpu_has_fxsr) {
+		memset(&fx_scratch, 0, sizeof(struct i387_fxsave_struct));
+		asm volatile("fxsave %0" : "+m" (fx_scratch));
+		mask = fx_scratch.mxcsr_mask;
+		if (mask == 0)
+			mask = 0x0000ffbf;
+	}
+	mxcsr_feature_mask &= mask;
+}
+
+static void fpstate_xstate_init_size(void)
+{
+	/*
+	 * Note that xstate_size might be overwriten later during
+	 * xsave_init().
+	 */
+
+	if (!cpu_has_fpu) {
+		/*
+		 * Disable xsave as we do not support it if i387
+		 * emulation is enabled.
+		 */
+		setup_clear_cpu_cap(X86_FEATURE_XSAVE);
+		setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);
+		xstate_size = sizeof(struct i387_soft_struct);
+		return;
+	}
+
+	if (cpu_has_fxsr)
+		xstate_size = sizeof(struct i387_fxsave_struct);
+	else
+		xstate_size = sizeof(struct i387_fsave_struct);
+}
+
+/*
+ * Called on the boot CPU at bootup to set up the initial FPU state that
+ * is later cloned into all processes.
+ *
+ * Also called on secondary CPUs to set up the FPU state of their
+ * idle threads.
+ */
+void fpu__cpu_init(void)
+{
+	unsigned long cr0;
+	unsigned long cr4_mask = 0;
+
+#ifndef CONFIG_MATH_EMULATION
+	if (!cpu_has_fpu) {
+		pr_emerg("No FPU found and no math emulation present\n");
+		pr_emerg("Giving up\n");
+		for (;;)
+			asm volatile("hlt");
+	}
+#endif
+	if (cpu_has_fxsr)
+		cr4_mask |= X86_CR4_OSFXSR;
+	if (cpu_has_xmm)
+		cr4_mask |= X86_CR4_OSXMMEXCPT;
+	if (cr4_mask)
+		cr4_set_bits(cr4_mask);
+
+	cr0 = read_cr0();
+	cr0 &= ~(X86_CR0_TS|X86_CR0_EM); /* clear TS and EM */
+	if (!cpu_has_fpu)
+		cr0 |= X86_CR0_EM;
+	write_cr0(cr0);
+
+	/*
+	 * fpstate_xstate_init_size() is only called once, to avoid overriding
+	 * 'xstate_size' during (secondary CPU) bootup or during CPU hotplug.
+	 */
+	if (xstate_size == 0)
+		fpstate_xstate_init_size();
+
+	mxcsr_feature_mask_init();
+	xsave_init();
+	eager_fpu_init();
+}