Commit-ID: 5fc960380ea44ba529c78b558b6cd4250e5e1958
Gitweb: http://git.kernel.org/tip/5fc960380ea44ba529c78b558b6cd4250e5e1958
Author: Ingo Molnar <mingo@xxxxxxxxxx>
AuthorDate: Sat, 22 Aug 2015 09:52:06 +0200
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Sat, 22 Aug 2015 10:02:04 +0200
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@xxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Quentin Casasnovas <quentin.casasnovas@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
arch/x86/kernel/fpu/init.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index 1e173f6..d14e9ac 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");
}
/*
--
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