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From: Borislav Petkov <bp@alien8.de>
To: Ingo Molnar <mingo@kernel.org>
Cc: "Bryan O'Donoghue" <pure.logic@nexus-software.ie>,
	Andy Lutomirski <luto@amacapital.net>,
	Andy Shevchenko <andy.shevchenko@gmail.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"x86@kernel.org" <x86@kernel.org>,
	Fenghua Yu <fenghua.yu@intel.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Oleg Nesterov <oleg@redhat.com>,
	"Yu, Yu-cheng" <yu-cheng.yu@intel.com>
Subject: [PATCH] x86/FPU: Fix FPU handling on legacy FPU machines
Date: Fri, 11 Mar 2016 12:32:06 +0100
Message-ID: <20160311113206.GD4312@pd.tnic> (raw)
In-Reply-To: <20160311112610.GC4312@pd.tnic>

486 cores like Intel Quark support only the very old, legacy x87 FPU
(FSAVE/FRSTOR, CPUID bit FXSR is not set). And our FPU code wasn't
handling the saving and restoring there properly. First, Andy Shevchenko
reported a splat:

  WARNING: CPU: 0 PID: 823 at arch/x86/include/asm/fpu/internal.h:163 fpu__clear+0x8c/0x160

which was us trying to execute FXRSTOR on those machines even though
they don't support it.

After taking care of that, Bryan O'Donoghue reported that a simple FPU
test still failed because we weren't initializing the FPU state properly
on those machines.

Take care of all that.

Reported-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reported-and-tested-by: Bryan O'Donoghue <pure.logic@nexus-software.ie>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/kernel/fpu/core.c | 4 +++-
 arch/x86/kernel/fpu/init.c | 2 +-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index dea8e76d60c6..8e37cc8a539a 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -474,8 +474,10 @@ static inline void copy_init_fpstate_to_fpregs(void)
 {
 	if (use_xsave())
 		copy_kernel_to_xregs(&init_fpstate.xsave, -1);
-	else
+	else if (static_cpu_has(X86_FEATURE_FXSR))
 		copy_kernel_to_fxregs(&init_fpstate.fxsave);
+	else
+		copy_kernel_to_fregs(&init_fpstate.fsave);
 }
 
 /*
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index e12cc0ad368e..c835f61d5feb 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -134,7 +134,7 @@ static void __init fpu__init_system_generic(void)
 	 * Set up the legacy init FPU context. (xstate init might overwrite this
 	 * with a more modern format, if the CPU supports it.)
 	 */
-	fpstate_init_fxstate(&init_fpstate.fxsave);
+	fpstate_init(&init_fpstate);
 
 	fpu__init_system_mxcsr();
 }
-- 
2.3.5


-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.

  reply index

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-03-10 10:46 Got FPU related warning on Intel Quark during boot Andy Shevchenko
2016-03-10 11:19 ` Ingo Molnar
2016-03-10 12:48   ` Andy Shevchenko
2016-03-10 12:56     ` Borislav Petkov
2016-03-10 13:31       ` Andy Shevchenko
2016-03-10 14:59         ` Borislav Petkov
2016-03-10 15:22           ` Andy Shevchenko
2016-03-10 15:45             ` Bryan O'Donoghue
2016-03-10 16:49               ` Borislav Petkov
2016-03-10 17:15                 ` Bryan O'Donoghue
2016-03-10 19:06                   ` Borislav Petkov
2016-03-11  1:31               ` Andy Lutomirski
2016-03-11 10:50                 ` Bryan O'Donoghue
2016-03-11  1:39           ` Andy Lutomirski
2016-03-11  9:08             ` Ingo Molnar
2016-03-11  9:48               ` Borislav Petkov
2016-03-11 11:02                 ` Bryan O'Donoghue
2016-03-11 11:26                   ` Borislav Petkov
2016-03-11 11:32                     ` Borislav Petkov [this message]
2016-03-11 18:32                       ` [PATCH] x86/FPU: Fix FPU handling on legacy FPU machines Linus Torvalds
2016-03-11 22:03                         ` Borislav Petkov
2016-03-11 22:07                           ` Dave Hansen
2016-03-11 22:20                             ` Borislav Petkov
2016-03-12 17:21                               ` Andy Lutomirski
2016-03-12 17:47                                 ` Borislav Petkov
2016-03-12 12:04                           ` Bryan O'Donoghue
2016-03-12 12:27                             ` Borislav Petkov
2016-03-12 15:17                           ` Ingo Molnar
2016-03-22 22:03                           ` Maciej W. Rozycki
2016-03-12 15:08                         ` Ingo Molnar
2016-03-12 15:12                           ` Ingo Molnar
2016-03-12 15:16                       ` [tip:x86/urgent] x86/fpu: Fix eager-FPU " tip-bot for Borislav Petkov

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