x86/fpu: Fix eager-FPU handling on legacy FPU machines

i486 derived 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 in the 'eagerfpu' case.

So after we made eagerfpu the default for all CPU types:

  58122bf1d856 x86/fpu: Default eagerfpu=on on all CPUs

these old FPU designs broke. 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-and-tested-by: Bryan O'Donoghue <pure.logic@nexus-software.ie>
Reported-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Yu-cheng <yu-cheng.yu@intel.com>
Link: http://lkml.kernel.org/r/20160311113206.GD4312@pd.tnic
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index d25097c3fc1d1af8af35c156f05121f9f4d46a94..d5804adfa6da6c3d495b124faf47c288e2c0c6cf 100644 (file)
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -409,8 +409,10 @@ 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 9ee7e307b18f3eca16f1acc0e76ff9c5f4beb8e4..bd08fb77073d833ec8f1e27bc67d20fa37b559dc 100644 (file)
--- 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();
 }