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>
diff --git a/arch/i386/kernel/cpu/common.c b/arch/i386/kernel/cpu/common.c
index 2799baa..b2f24d5 100644
--- a/arch/i386/kernel/cpu/common.c
+++ b/arch/i386/kernel/cpu/common.c
@@ -184,7 +184,16 @@
static int __init x86_fxsr_setup(char * s)
{
+ /* Tell all the other CPU's to not use it... */
disable_x86_fxsr = 1;
+
+ /*
+ * ... and clear the bits early in the boot_cpu_data
+ * so that the bootup process doesn't try to do this
+ * either.
+ */
+ clear_bit(X86_FEATURE_FXSR, boot_cpu_data.x86_capability);
+ clear_bit(X86_FEATURE_XMM, boot_cpu_data.x86_capability);
return 1;
}
__setup("nofxsr", x86_fxsr_setup);