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authorIngo Molnar <mingo@kernel.org>2015-07-04 09:58:19 +0200
committerIngo Molnar <mingo@kernel.org>2015-07-04 10:05:56 +0200
commitb96fecbfa8c88b057e2bbf10021521c232bb3650 (patch)
tree9b5d855085336ae9ab5b9c5ff7f6972b13f181de
parent864d5bb957138d1ed9641a5eff7849a56ddadc16 (diff)
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>
-rw-r--r--arch/x86/kernel/fpu/init.c7
1 files changed, 4 insertions, 3 deletions
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index fc878fee6a51..32826791e675 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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