• Ingo Molnar's avatar
    x86/fpu: Fix boot crash in the early FPU code · b96fecbf
    Ingo Molnar authored
    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:
    
       91a8c2a5 ("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: default avatarJan Kara <jack@suse.cz>
    Reported-bisected-and-tested-by: default avatarThomas 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.comSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    b96fecbf
init.c 8.73 KB