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From: Andy Lutomirski <luto@kernel.org>
To: x86@kernel.org, linux-kernel@vger.kernel.org
Cc: Borislav Petkov <bp@alien8.de>, Fenghua Yu <fenghua.yu@intel.com>,
	Oleg Nesterov <oleg@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>,
	yu-cheng yu <yu-cheng.yu@intel.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Rik van Riel <riel@redhat.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Andy Lutomirski <luto@kernel.org>
Subject: [PATCH v2 1/5] x86/fpu: Fix math emulation in eager fpu mode
Date: Sun, 24 Jan 2016 14:38:06 -0800	[thread overview]
Message-ID: <b4b8d112436bd6fab866e1b4011131507e8d7fbe.1453675014.git.luto@kernel.org> (raw)
In-Reply-To: <cover.1453675014.git.luto@kernel.org>
In-Reply-To: <cover.1453675014.git.luto@kernel.org>

Systems without an FPU are generally old and therefore use lazy FPU
switching.  Unsurprisingly, math emulation in eager FPU mode is a
bit buggy.  Fix it.

There were two bugs involving kernel code trying to use the FPU
registers in eager mode even if they didn't exist and one BUG_ON
that was incorrect.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 arch/x86/include/asm/fpu/internal.h | 3 ++-
 arch/x86/kernel/fpu/core.c          | 2 +-
 arch/x86/kernel/traps.c             | 1 -
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h
index 0fd440df63f1..a1f78a9fbf41 100644
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -589,7 +589,8 @@ switch_fpu_prepare(struct fpu *old_fpu, struct fpu *new_fpu, int cpu)
 	 * If the task has used the math, pre-load the FPU on xsave processors
 	 * or if the past 5 consecutive context-switches used math.
 	 */
-	fpu.preload = new_fpu->fpstate_active &&
+	fpu.preload = static_cpu_has(X86_FEATURE_FPU) &&
+		      new_fpu->fpstate_active &&
 		      (use_eager_fpu() || new_fpu->counter > 5);
 
 	if (old_fpu->fpregs_active) {
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index d25097c3fc1d..08e1e11a05ca 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -423,7 +423,7 @@ void fpu__clear(struct fpu *fpu)
 {
 	WARN_ON_FPU(fpu != &current->thread.fpu); /* Almost certainly an anomaly */
 
-	if (!use_eager_fpu()) {
+	if (!use_eager_fpu() || !static_cpu_has(X86_FEATURE_FPU)) {
 		/* FPU state will be reallocated lazily at the first use. */
 		fpu__drop(fpu);
 	} else {
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index ade185a46b1d..87f80febf477 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -750,7 +750,6 @@ dotraplinkage void
 do_device_not_available(struct pt_regs *regs, long error_code)
 {
 	RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
-	BUG_ON(use_eager_fpu());
 
 #ifdef CONFIG_MATH_EMULATION
 	if (read_cr0() & X86_CR0_EM) {
-- 
2.5.0

  reply	other threads:[~2016-01-24 22:39 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-01-24 22:38 [PATCH v2 0/5] x86/fpu: eagerfpu fixes, speedups, and default enablement Andy Lutomirski
2016-01-24 22:38 ` Andy Lutomirski [this message]
2016-02-09 16:10   ` [tip:x86/fpu] x86/fpu: Fix math emulation in eager fpu mode tip-bot for Andy Lutomirski
2016-01-24 22:38 ` [PATCH v2 2/5] x86/fpu: Fix FNSAVE usage in eagerfpu mode Andy Lutomirski
2016-01-25 15:40   ` Dave Hansen
2016-01-25 17:25     ` Andy Lutomirski
2016-01-25 17:26       ` Dave Hansen
2016-02-09 16:10   ` [tip:x86/fpu] " tip-bot for Andy Lutomirski
2016-01-24 22:38 ` [PATCH v2 3/5] x86/fpu: Fold fpu_copy into fpu__copy Andy Lutomirski
2016-02-09 16:10   ` [tip:x86/fpu] x86/fpu: Fold fpu_copy() into fpu__copy() tip-bot for Andy Lutomirski
2016-01-24 22:38 ` [PATCH v2 4/5] x86/fpu: Speed up lazy FPU restores slightly Andy Lutomirski
2016-02-09 16:11   ` [tip:x86/fpu] " tip-bot for Andy Lutomirski
2016-01-24 22:38 ` [PATCH v2 5/5] x86/fpu: Default eagerfpu=on on all CPUs Andy Lutomirski
2016-02-09 16:11   ` [tip:x86/fpu] " tip-bot for Andy Lutomirski

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