From: "Bryan O'Donoghue" <pure.logic@nexus-software.ie>
To: Andy Shevchenko <andy.shevchenko@gmail.com>,
Borislav Petkov <bp@alien8.de>
Cc: Ingo Molnar <mingo@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"x86@kernel.org" <x86@kernel.org>,
Andy Lutomirski <luto@amacapital.net>,
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: Re: Got FPU related warning on Intel Quark during boot
Date: Thu, 10 Mar 2016 15:45:21 +0000 [thread overview]
Message-ID: <1457624721.5784.0.camel@nexus-software.ie> (raw)
In-Reply-To: <CAHp75VetABhKYverANgLwsHS+L6T8nxQqcbDGT8fwN8xrURJ6Q@mail.gmail.com>
[-- Attachment #1: Type: text/plain, Size: 3153 bytes --]
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
root@galileo:~# uname -aLinux galileo 4.5.0-rc7-next-20160310+ #185 Thu
Mar 10 15:11:10 GMT 2016 i586 GNU/Linux
[-- Attachment #2: fpu.c --]
[-- Type: text/x-csrc, Size: 555 bytes --]
#include <stdio.h>
#include <signal.h>
#include <string.h>
float a = 0;
void handler(int signum, siginfo_t *info, void *ptr)
{
printf("%s value of variable is %f\n", __func__, a);
}
int main(int argc, char *argv[])
{
struct sigaction sig;
float f = 10, g = 10.1f;
memset(&sig, 0x00, sizeof(sig));
sig.sa_sigaction = handler;
sig.sa_flags = SA_SIGINFO;
sigaction(SIGTERM, &sig, NULL);
sigaction(SIGINT, &sig, NULL);
printf("f is %f g is %f\n", f, g);
while(1) {
sleep(1);
printf("Double value is %f\n", a);
a += 0.1f;
}
return 0;
}
next prev parent reply other threads:[~2016-03-10 15:45 UTC|newest]
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 [this message]
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 ` [PATCH] x86/FPU: Fix FPU handling on legacy FPU machines Borislav Petkov
2016-03-11 18:32 ` 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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