[PATCH 3/4] x86/fpu/xstate: Keep init_fpstate.xsave.header.xfeatures as zero for init optimization

[Yu-cheng Yu <yu-cheng.yu@intel.com>]

From: Fenghua Yu <fenghua.yu@intel.com>

Keep init_fpstate.xsave.header.xfeatures as zero for init optimization.
This is important for init optimization that is implemented in processor.
If a bit corresponding to an xstate in xstate_bv is 0, it means the
xstate is in init status and will not be read from memory to the processor
during XRSTOR/XRSTORS instruction. This largely impacts context switch
performance.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Reviewed-by: Dave Hansen <dave.hansen@intel.com>
---
 arch/x86/kernel/fpu/xstate.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 875afe9..5239d4d 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -329,13 +329,11 @@ static void __init setup_init_fpu_buf(void)
 	setup_xstate_features();
 	print_xstate_features();
 
-	if (cpu_has_xsaves) {
+	if (cpu_has_xsaves)
 		init_fpstate.xsave.header.xcomp_bv = (u64)1 << 63 | xfeatures_mask;
-		init_fpstate.xsave.header.xfeatures = xfeatures_mask;
-	}
 
 	/*
-	 * Init all the features state with header_bv being 0x0
+	 * Init all the features state with header.xfeatures being 0x0
 	 */
 	copy_kernel_to_xregs_booting(&init_fpstate.xsave);
 
-- 
1.9.1