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>

2 files changed, 15 insertions, 6 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index e8f7faaa4571..46a6a8288dec 100644
--- a/Documentation/kernel-parameters.txt
+++ b/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
diff --git a/arch/x86/kernel/xsave.c b/arch/x86/kernel/xsave.c
index e99f75439f6d..4e89b3dd408d 100644
--- a/arch/x86/kernel/xsave.c
+++ b/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;