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authorIngo Molnar <mingo@kernel.org>2015-08-22 09:52:06 +0200
committerIngo Molnar <mingo@kernel.org>2015-08-22 10:02:04 +0200
commit5fc960380ea44ba529c78b558b6cd4250e5e1958 (patch)
tree2c8439a9d85b9ad4084adeb28a41e3a0ccbc2023 /arch
parente43d0189ac02415fe4487f79fc35e8f147e9ea0d (diff)
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>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/kernel/fpu/init.c7
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(&current->thread.fpu.state.soft);
+ else
+#endif
+ asm volatile ("fninit");
}
/*