x86, fpu: make eagerfpu= boot param tri-state

Add the "eagerfpu=auto" (that selects the default scheme in
enabling eagerfpu) which can override compiled-in boot parameters
like "eagerfpu=on/off" (that force enable/disable eagerfpu).

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Link: http://lkml.kernel.org/r/1347300665-6209-5-git-send-email-suresh.b.siddha@intel.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

Documentation/kernel-parameters.txt

@@ -1834,8 +1834,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			enabling legacy floating-point and sse state.
 
 	eagerfpu=	[X86]
-			on	enable eager fpu restore (default for xsaveopt)
+			on	enable eager fpu restore
 			off	disable eager fpu restore
+			auto	selects the default scheme, which automatically
+				enables eagerfpu restore for xsaveopt.
 
 	nohlt		[BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
 			wfi(ARM) instruction doesn't work correctly and not to

arch/x86/kernel/xsave.c

@@ -508,13 +508,15 @@ static void __init setup_init_fpu_buf(void)
 	xsave_state(init_xstate_buf, -1);
 }
 
-static int disable_eagerfpu;
+static enum { AUTO, ENABLE, DISABLE } eagerfpu = AUTO;
 static int __init eager_fpu_setup(char *s)
 {
 	if (!strcmp(s, "on"))
-		setup_force_cpu_cap(X86_FEATURE_EAGER_FPU);
+		eagerfpu = ENABLE;
 	else if (!strcmp(s, "off"))
-		disable_eagerfpu = 1;
+		eagerfpu = DISABLE;
+	else if (!strcmp(s, "auto"))
+		eagerfpu = AUTO;
 	return 1;
 }
 __setup("eagerfpu=", eager_fpu_setup);
@@ -557,8 +559,9 @@ static void __init xstate_enable_boot_cpu(void)
 	prepare_fx_sw_frame();
 	setup_init_fpu_buf();
 
-	if (cpu_has_xsaveopt && !disable_eagerfpu)
-		setup_force_cpu_cap(X86_FEATURE_EAGER_FPU);
+	/* Auto enable eagerfpu for xsaveopt */
+	if (cpu_has_xsaveopt && eagerfpu != DISABLE)
+		eagerfpu = ENABLE;
 
 	pr_info("enabled xstate_bv 0x%llx, cntxt size 0x%x\n",
 		pcntxt_mask, xstate_size);
@@ -598,6 +601,10 @@ void __cpuinit eager_fpu_init(void)
 
 	clear_used_math();
 	current_thread_info()->status = 0;
+
+	if (eagerfpu == ENABLE)
+		setup_force_cpu_cap(X86_FEATURE_EAGER_FPU);
+
 	if (!cpu_has_eager_fpu) {
 		stts();
 		return;