x86, fpu: enable eagerfpu by default for xsaveopt

xsaveopt/xrstor support optimized state save/restore by tracking the
INIT state and MODIFIED state during context-switch.

Enable eagerfpu by default for processors supporting xsaveopt.
Can be disabled by passing "eagerfpu=off" boot parameter.
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Link: http://lkml.kernel.org/r/1347300665-6209-3-git-send-email-suresh.b.siddha@intel.comSigned-off-by: H. Peter Anvin <hpa@linux.intel.com>

Documentation/kernel-parameters.txt

@@ -1834,7 +1834,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			enabling legacy floating-point and sse state.
 
 	eagerfpu=	[X86]
-			on	enable eager fpu restore
+			on	enable eager fpu restore (default for xsaveopt)
 			off	disable eager fpu restore
 
 	nohlt		[BUGS=ARM,SH] Tells the kernel that the sleep(SH) or

arch/x86/include/asm/cpufeature.h

@@ -300,6 +300,7 @@ extern const char * const x86_power_flags[32];
 #define cpu_has_xmm4_2		boot_cpu_has(X86_FEATURE_XMM4_2)
 #define cpu_has_x2apic		boot_cpu_has(X86_FEATURE_X2APIC)
 #define cpu_has_xsave		boot_cpu_has(X86_FEATURE_XSAVE)
+#define cpu_has_xsaveopt	boot_cpu_has(X86_FEATURE_XSAVEOPT)
 #define cpu_has_osxsave		boot_cpu_has(X86_FEATURE_OSXSAVE)
 #define cpu_has_hypervisor	boot_cpu_has(X86_FEATURE_HYPERVISOR)
 #define cpu_has_pclmulqdq	boot_cpu_has(X86_FEATURE_PCLMULQDQ)

arch/x86/kernel/xsave.c

@@ -557,6 +557,9 @@ 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);
+
 	pr_info("enabled xstate_bv 0x%llx, cntxt size 0x%x\n",
 		pcntxt_mask, xstate_size);
 }