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| author | Ingo Molnar <mingo@kernel.org> | 2015-08-22 09:52:06 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2015-08-22 10:02:04 +0200 |
| commit | 5fc960380ea44ba529c78b558b6cd4250e5e1958 (patch) | |
| tree | 2c8439a9d85b9ad4084adeb28a41e3a0ccbc2023 | |
| parent | x86/idle: Restore trace_cpu_idle to mwait_idle() calls (diff) | |
| download | linux-5fc960380ea44ba529c78b558b6cd4250e5e1958.tar.xz linux-5fc960380ea44ba529c78b558b6cd4250e5e1958.zip | |
x86/fpu/math-emu: Fix math-emu boot crash
On a math-emu bootup the following crash occurs:
Initializing CPU#0
------------[ cut here ]------------
kernel BUG at arch/x86/kernel/traps.c:779!
invalid opcode: 0000 [#1] SMP
[...]
EIP is at do_device_not_available+0xe/0x70
[...]
Call Trace:
[<c18238e6>] error_code+0x5a/0x60
[<c1002bd0>] ? math_error+0x140/0x140
[<c100bbd9>] ? fpu__init_cpu+0x59/0xa0
[<c1012322>] cpu_init+0x202/0x330
[<c104509f>] ? __native_set_fixmap+0x1f/0x30
[<c1b56ab0>] trap_init+0x305/0x346
[<c1b548af>] start_kernel+0x1a5/0x35d
[<c1b542b4>] i386_start_kernel+0x82/0x86
The reason is that in the following commit:
b1276c48e91b ("x86/fpu: Initialize fpregs in fpu__init_cpu_generic()")
I failed to consider math-emu's limitation that it cannot execute the
FNINIT instruction in kernel mode.
The long term fix might be to allow math-emu to execute (certain) kernel
mode FPU instructions, but for now apply the safe (albeit somewhat ugly)
fix: initialize the emulation state explicitly without trapping out to
the FPU emulator.
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: Linus Torvalds <torvalds@linux-foundation.org>
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: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
| -rw-r--r-- | arch/x86/kernel/fpu/init.c | 7 |
1 files changed, 6 insertions, 1 deletions
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c index 1e173f6285c7..d14e9ac3235a 100644 --- a/arch/x86/kernel/fpu/init.c +++ b/arch/x86/kernel/fpu/init.c @@ -40,7 +40,12 @@ static void fpu__init_cpu_generic(void) write_cr0(cr0); /* Flush out any pending x87 state: */ - asm volatile ("fninit"); +#ifdef CONFIG_MATH_EMULATION + if (!cpu_has_fpu) + fpstate_init_soft(¤t->thread.fpu.state.soft); + else +#endif + asm volatile ("fninit"); } /* |