linux-kernel - [PATCH] x86/fpu: Finish excising 'eagerfpu'

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Date:   Mon, 17 Oct 2016 14:40:11 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     x86@...nel.org
Cc:     Rik van Riel <riel@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>
Subject: [PATCH] x86/fpu: Finish excising 'eagerfpu'

Now that eagerfpu= is gone, remove it from the docs and some
comments.  Also sync the changes to tools/.

Fixes: ca6938a1cd8a ("x86/fpu: Hard-disable lazy FPU mode")
Signed-off-by: Andy Lutomirski <luto@...nel.org>
Message-Id: <6c6e48fa5b6a51a70bf1ffd149a7125c5fd349be.1475859005.git.luto@...nel.org>
---
 Documentation/kernel-parameters.txt      |  6 ------
 arch/x86/include/asm/cpufeatures.h       |  1 -
 arch/x86/include/asm/fpu/types.h         | 23 -----------------------
 arch/x86/mm/pkeys.c                      |  3 +--
 tools/arch/x86/include/asm/cpufeatures.h |  1 -
 5 files changed, 1 insertion(+), 33 deletions(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 37babf91f2cb..459b301137c2 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1074,12 +1074,6 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 	nopku		[X86] Disable Memory Protection Keys CPU feature found
 			in some Intel CPUs.
 
-	eagerfpu=	[X86]
-			on	enable eager fpu restore
-			off	disable eager fpu restore
-			auto	selects the default scheme, which automatically
-				enables eagerfpu restore for xsaveopt.
-
 	module.async_probe [KNL]
 			Enable asynchronous probe on this module.
 
diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index b212b862314a..2599222215c9 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -104,7 +104,6 @@
 #define X86_FEATURE_EXTD_APICID	( 3*32+26) /* has extended APICID (8 bits) */
 #define X86_FEATURE_AMD_DCM     ( 3*32+27) /* multi-node processor */
 #define X86_FEATURE_APERFMPERF	( 3*32+28) /* APERFMPERF */
-/* free, was #define X86_FEATURE_EAGER_FPU	( 3*32+29) * "eagerfpu" Non lazy FPU restore */
 #define X86_FEATURE_NONSTOP_TSC_S3 ( 3*32+30) /* TSC doesn't stop in S3 state */
 
 /* Intel-defined CPU features, CPUID level 0x00000001 (ecx), word 4 */
diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h
index e31332d6f0e8..3c80f5b9c09d 100644
--- a/arch/x86/include/asm/fpu/types.h
+++ b/arch/x86/include/asm/fpu/types.h
@@ -329,29 +329,6 @@ struct fpu {
 	 * the registers in the FPU are more recent than this state
 	 * copy. If the task context-switches away then they get
 	 * saved here and represent the FPU state.
-	 *
-	 * After context switches there may be a (short) time period
-	 * during which the in-FPU hardware registers are unchanged
-	 * and still perfectly match this state, if the tasks
-	 * scheduled afterwards are not using the FPU.
-	 *
-	 * This is the 'lazy restore' window of optimization, which
-	 * we track though 'fpu_fpregs_owner_ctx' and 'fpu->last_cpu'.
-	 *
-	 * We detect whether a subsequent task uses the FPU via setting
-	 * CR0::TS to 1, which causes any FPU use to raise a #NM fault.
-	 *
-	 * During this window, if the task gets scheduled again, we
-	 * might be able to skip having to do a restore from this
-	 * memory buffer to the hardware registers - at the cost of
-	 * incurring the overhead of #NM fault traps.
-	 *
-	 * Note that on modern CPUs that support the XSAVEOPT (or other
-	 * optimized XSAVE instructions), we don't use #NM traps anymore,
-	 * as the hardware can track whether FPU registers need saving
-	 * or not. On such CPUs we activate the non-lazy ('eagerfpu')
-	 * logic, which unconditionally saves/restores all FPU state
-	 * across context switches. (if FPU state exists.)
 	 */
 	union fpregs_state		state;
 	/*
diff --git a/arch/x86/mm/pkeys.c b/arch/x86/mm/pkeys.c
index f88ce0e5efd9..2dab69a706ec 100644
--- a/arch/x86/mm/pkeys.c
+++ b/arch/x86/mm/pkeys.c
@@ -141,8 +141,7 @@ u32 init_pkru_value = PKRU_AD_KEY( 1) | PKRU_AD_KEY( 2) | PKRU_AD_KEY( 3) |
  * Called from the FPU code when creating a fresh set of FPU
  * registers.  This is called from a very specific context where
  * we know the FPU regstiers are safe for use and we can use PKRU
- * directly.  The fact that PKRU is only available when we are
- * using eagerfpu mode makes this possible.
+ * directly.
  */
 void copy_init_pkru_to_fpregs(void)
 {
diff --git a/tools/arch/x86/include/asm/cpufeatures.h b/tools/arch/x86/include/asm/cpufeatures.h
index 1188bc849ee3..2599222215c9 100644
--- a/tools/arch/x86/include/asm/cpufeatures.h
+++ b/tools/arch/x86/include/asm/cpufeatures.h
@@ -104,7 +104,6 @@
 #define X86_FEATURE_EXTD_APICID	( 3*32+26) /* has extended APICID (8 bits) */
 #define X86_FEATURE_AMD_DCM     ( 3*32+27) /* multi-node processor */
 #define X86_FEATURE_APERFMPERF	( 3*32+28) /* APERFMPERF */
-#define X86_FEATURE_EAGER_FPU	( 3*32+29) /* "eagerfpu" Non lazy FPU restore */
 #define X86_FEATURE_NONSTOP_TSC_S3 ( 3*32+30) /* TSC doesn't stop in S3 state */
 
 /* Intel-defined CPU features, CPUID level 0x00000001 (ecx), word 4 */
-- 
2.7.4