linux-kernel - [PATCH v2 9/9] x86/xsaves: Re-enable XSAVES

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Date:	Thu, 25 Feb 2016 12:26:20 -0800
From:	Yu-cheng Yu <yu-cheng.yu@...el.com>
To:	x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Cc:	Dave Hansen <dave.hansen@...ux.intel.com>,
	Andy Lutomirski <luto@...nel.org>,
	Borislav Petkov <bp@...e.de>,
	Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>,
	"Ravi V. Shankar" <ravi.v.shankar@...el.com>,
	Fenghua Yu <fenghua.yu@...el.com>,
	Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: [PATCH v2 9/9] x86/xsaves: Re-enable XSAVES

We did not handle XSAVES* instructions correctly. There were issues in
converting between standard and compacted format when interfacing with
user-space. These issues have been corrected.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
---
 arch/x86/kernel/fpu/init.c | 16 ++++------------
 1 file changed, 4 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index b5952d5..21e0d52 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -228,19 +228,11 @@ static void __init fpu__init_system_xstate_size_legacy(void)
 	user_xstate_size = kernel_xstate_size;
 
 	/*
-	 * Quirk: we don't yet handle the XSAVES* instructions
-	 * correctly, as we don't correctly convert between
-	 * standard and compacted format when interfacing
-	 * with user-space - so disable it for now.
-	 *
-	 * The difference is small: with recent CPUs the
-	 * compacted format is only marginally smaller than
-	 * the standard FPU state format.
-	 *
-	 * ( This is easy to backport while we are fixing
-	 *   XSAVES* support. )
+	 * Most recent CPUs supporting XSAVES can run 64-bit mode.
+	 * Enable XSAVES for 64-bit.
 	 */
-	setup_clear_cpu_cap(X86_FEATURE_XSAVES);
+	if (!config_enabled(CONFIG_X86_64))
+		setup_clear_cpu_cap(X86_FEATURE_XSAVES);
 }
 
 /*
-- 
1.9.1