Messages in this thread Patch in this message | | | Date | Sat, 4 Jul 2015 01:09:34 -0700 | From | tip-bot for Ingo Molnar <> | Subject | [tip:x86/urgent] x86/fpu: Fix boot crash in the early FPU code |
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Commit-ID: b96fecbfa8c88b057e2bbf10021521c232bb3650 Gitweb: http://git.kernel.org/tip/b96fecbfa8c88b057e2bbf10021521c232bb3650 Author: Ingo Molnar <mingo@kernel.org> AuthorDate: Sat, 4 Jul 2015 09:58:19 +0200 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Sat, 4 Jul 2015 10:05:56 +0200
x86/fpu: Fix boot crash in the early FPU code
Jan Kara and Thomas Gleixner reported boot crashes in the FPU code:
general protection fault: 0000 [#1] SMP RIP: 0010:[<ffffffff81048a6c>] [<ffffffff81048a6c>] mxcsr_feature_mask_init+0x1c/0x40
2b:* 0f ae 85 00 fe ff ff fxsave -0x200(%rbp)
and bisected it down to the following FPU commit:
91a8c2a5b43f ("x86/fpu: Clean up and fix MXCSR handling")
The reason is that the on-stack FPU registers state variable, used by the FXSAVE instruction, did not have the required minimum alignment of 16 bytes, causing the general protection fault.
This is most likely a GCC bug in older GCC versions, but the offending commit also added a bogus extra 32-byte alignment (which GCC ignored too).
So fix this bug by making the variable static again, but also mark it __initdata this time, because fpu__init_system_mxcsr() is now an __init function.
Reported-and-bisected-by: Jan Kara <jack@suse.cz> Reported-bisected-and-tested-by: Thomas Gleixner <tglx@linutronix.de> 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: Jan Kara <jack@suse.cz> 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> Link: http://lkml.kernel.org/r/20150704075819.GA9201@gmail.com Signed-off-by: Ingo Molnar <mingo@kernel.org> --- arch/x86/kernel/fpu/init.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c index fc878fe..3282679 100644 --- a/arch/x86/kernel/fpu/init.c +++ b/arch/x86/kernel/fpu/init.c @@ -95,11 +95,12 @@ static void __init fpu__init_system_mxcsr(void) unsigned int mask = 0; if (cpu_has_fxsr) { - struct fxregs_state fx_tmp __aligned(32) = { }; + /* Static because GCC does not get 16-byte stack alignment right: */ + static struct fxregs_state fxregs __initdata; - asm volatile("fxsave %0" : "+m" (fx_tmp)); + asm volatile("fxsave %0" : "+m" (fxregs)); - mask = fx_tmp.mxcsr_mask; + mask = fxregs.mxcsr_mask; /* * If zero then use the default features mask,
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