Messages in this thread | | | Subject | Re: Got FPU related warning on Intel Quark during boot | From | Bryan O'Donoghue <> | Date | Fri, 11 Mar 2016 10:50:38 +0000 |
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On Thu, 2016-03-10 at 17:31 -0800, Andy Lutomirski wrote: > On Thu, Mar 10, 2016 at 7:45 AM, Bryan O'Donoghue > <pure.logic@nexus-software.ie> wrote: > > On Thu, 2016-03-10 at 17:22 +0200, Andy Shevchenko wrote: > > > On Thu, Mar 10, 2016 at 4:59 PM, Borislav Petkov <bp@alien8.de> > > > wrote: > > > > On Thu, Mar 10, 2016 at 03:31:43PM +0200, Andy Shevchenko > > > > wrote: > > > > > Looks like it lacks that one. > > > > > > > > > > # grep -i fxsr /proc/cpuinfo; echo $? > > > > > 1 > > > > > > > > Ok, so looking at where the warning comes from: > > > > > > > > [ 14.714533] WARNING: CPU: 0 PID: 823 at > > > > arch/x86/include/asm/fpu/internal.h:163 fpu__clear+0x8c/0x160 > > > > > > > > static inline void copy_kernel_to_fxregs(struct fxregs_state > > > > *fx) > > > > { > > > > int err; > > > > > > > > if (config_enabled(CONFIG_X86_32)) { > > > > err = check_insn(fxrstor %[fx], "=m" (*fx), > > > > [fx] > > > > "m" (*fx)); > > > > ^^^^^^^^^^^^^^^^^ > > > > } else { > > > > > > > > ... > > > > > > > > /* Copying from a kernel buffer to FPU registers should > > > > never fail: */ > > > > WARN_ON_FPU(err); > > > > > > > > > > > > and the stacktrace is pretty clear: > > > > > > > > flush_thread > > > > > -> fpu__clear(&tsk->thread.fpu); > > > > |-> we are eager by default here: > > > > > > > > if (!use_eager_fpu() || > > > > !static_cpu_has(X86_FEATURE_FPU)) { > > > > /* FPU state will be reallocated lazily at the > > > > first use. */ > > > > fpu__drop(fpu); > > > > } else { > > > > > > > > --> we're in that branch. > > > > > > > > copy_init_fpstate_to_fpregs(); > > > > |-> copy_kernel_to_fxregs() > > > > > > > > > > > > I think we should use FRSTOR on quark, i.e., > > > > copy_kernel_to_fregs(). > > > > > > > > Does this untested wild guess even work? > > > > > > > > --- > > > > diff --git a/arch/x86/kernel/fpu/core.c > > > > b/arch/x86/kernel/fpu/core.c > > > > index dea8e76d60c6..bbafe5e8a1a6 100644 > > > > --- a/arch/x86/kernel/fpu/core.c > > > > +++ b/arch/x86/kernel/fpu/core.c > > > > @@ -474,8 +474,11 @@ 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); > > > > + > > > > > > Obviously redundant line, otherwise it indeed works > > > > > > Tested-by: Andy Shevchenko <andy.shevchenko@gmail.com> > > > > > > > } > > > > > > > > /* > > > > > > > > > > > > > It works but user-space FPU is broken; something's wrong with the > > initial state of the FPU regs - it looks as though they aren't > > being > > properly initialized and FPU context in the signal handler is wrong > > too. > > > > Linux 3.8.7: > > /root@galileo:~# ./fpu > > f is 10.000000 g is 10.100000 > > Double value is 0.000000 > > Double value is 0.100000 > > Double value is 0.200000 > > ^Chandler value of variable is 0.300000 > > Double value is 0.300000 > > Double value is 0.400000 > > > > Linux-next + Boris' fix: > > root@galileo:~# ./fpu > > f is -nan g is -nan > > Double value is 0.000000 > > Double value is 0.100000 > > Double value is 0.200000^C > > handler value of variable is -nan > > Double value is 0.300000 > > Double value is 0.400000^Z[1]+ Stopped > > > > Just to check: are you running the exact same compiled binary on both > kernels? Because your test case invokes undefined behavior, and I'm > a > bit surprised you get anything sensible from it. That being said, > the > f = -nan part is worrisome. > > --Andy
It's the same binary yes.
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