linux-kernel - [PATCH v2] x86/fpu: Revert earlier patch of Disable AVX when eagerfpu is off

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Date:	Wed,  9 Mar 2016 16:28:54 -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>,
	Leonid Shatz <leonid.shatz@...ellosystems.com>,
	Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: [PATCH v2] x86/fpu: Revert earlier patch of Disable AVX when eagerfpu is off

Because AVX is not stated in CR0 TS bit description, it was mistakenly
believed to be not supported for lazy context switch. This turns out to be
false. The earlier patch should be reverted.

Reference [1]:

Intel Software Developer's Manual Vol. 3A, Sec. 2.5 Control Registers:
TS Task Switched bit (bit 3 of CR0) -- Allows the saving of the x87 FPU/
MMX/SSE/SSE2/SSE3/SSSE3/SSE4 context on a task switch to be delayed until
an x87 FPU/MMX/SSE/SSE2/SSE3/SSSE3/SSE4 instruction is actually executed
by the new task.

Reference [2]:

Intel Software Developer's Manual Vol. 2A, Sec. 2.4 Instruction Exception
Specification. AVX instructions refer to exceptions by classes that
include #NM "Device Not Available" exception for lazy context switch.

Original patch:
    commit 394db20ca240741a08d472173db13d6f6a6e5a28 ("x86/fpu: Disable AVX
           when eagerfpu is off")

Reported-by: Leonid Shatz <leonid.shatz@...ellosystems.com>
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
---
 arch/x86/include/asm/fpu/xstate.h | 9 ++++-----
 arch/x86/kernel/fpu/init.c        | 6 ------
 2 files changed, 4 insertions(+), 11 deletions(-)

diff --git a/arch/x86/include/asm/fpu/xstate.h b/arch/x86/include/asm/fpu/xstate.h
index af30fde..f23cd8c 100644
--- a/arch/x86/include/asm/fpu/xstate.h
+++ b/arch/x86/include/asm/fpu/xstate.h
@@ -20,16 +20,15 @@
 
 /* Supported features which support lazy state saving */
 #define XFEATURE_MASK_LAZY	(XFEATURE_MASK_FP | \
-				 XFEATURE_MASK_SSE)
-
-/* Supported features which require eager state saving */
-#define XFEATURE_MASK_EAGER	(XFEATURE_MASK_BNDREGS | \
-				 XFEATURE_MASK_BNDCSR | \
+				 XFEATURE_MASK_SSE | \
 				 XFEATURE_MASK_YMM | \
 				 XFEATURE_MASK_OPMASK | \
 				 XFEATURE_MASK_ZMM_Hi256 | \
 				 XFEATURE_MASK_Hi16_ZMM)
 
+/* Supported features which require eager state saving */
+#define XFEATURE_MASK_EAGER	(XFEATURE_MASK_BNDREGS | XFEATURE_MASK_BNDCSR)
+
 /* All currently supported features */
 #define XCNTXT_MASK	(XFEATURE_MASK_LAZY | XFEATURE_MASK_EAGER)
 
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index 6d9f0a7..f0ab368 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -300,12 +300,6 @@ u64 __init fpu__get_supported_xfeatures_mask(void)
 static void __init fpu__clear_eager_fpu_features(void)
 {
 	setup_clear_cpu_cap(X86_FEATURE_MPX);
-	setup_clear_cpu_cap(X86_FEATURE_AVX);
-	setup_clear_cpu_cap(X86_FEATURE_AVX2);
-	setup_clear_cpu_cap(X86_FEATURE_AVX512F);
-	setup_clear_cpu_cap(X86_FEATURE_AVX512PF);
-	setup_clear_cpu_cap(X86_FEATURE_AVX512ER);
-	setup_clear_cpu_cap(X86_FEATURE_AVX512CD);
 }
 
 /*
-- 
1.9.1