x86: Fix booting with "no387 nofxsr"
Jesper Juhl reported that testing the software math-emulation by forcing "no387" doesn't work on modern CPU's. The reason was two-fold: - you also need to pass in "nofxsr" to make sure that we not only don't touch the old i387 legacy hardware, it also needs to disable the modern XMM/FXSR sequences - "nofxsr" didn't actually clear the capability bits immediately, leaving the early boot sequence still using FXSR until we got to the identify_cpu() stage. This fixes the "nofxsr" flag to take effect immediately on the boot CPU. Debugging by Randy Dunlap Acked-by: Randy Dunlap <rdunlap@xenotime.net> Cc: Jesper Juhl <jesper.juhl@gmail.com> Cc: Andi Kleen <ak@suse.de> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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@ -184,7 +184,16 @@ static void __cpuinit get_cpu_vendor(struct cpuinfo_x86 *c, int early)
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static int __init x86_fxsr_setup(char * s)
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{
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/* Tell all the other CPU's to not use it... */
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disable_x86_fxsr = 1;
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/*
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* ... and clear the bits early in the boot_cpu_data
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* so that the bootup process doesn't try to do this
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* either.
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*/
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clear_bit(X86_FEATURE_FXSR, boot_cpu_data.x86_capability);
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clear_bit(X86_FEATURE_XMM, boot_cpu_data.x86_capability);
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return 1;
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}
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__setup("nofxsr", x86_fxsr_setup);
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