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x86: completely disable NOPL on 32 bits

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Completely disable NOPL on 32 bits.  It turns out that Microsoft
Virtual PC is so broken it can't even reliably *fail* in the presence
of NOPL.

This leaves the infrastructure in place but disables it
unconditionally.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
This commit is contained in:
H. Peter Anvin 2008-09-16 09:29:40 -07:00
parent 5132895f14
commit ba0593bf55
1 changed files with 4 additions and 20 deletions
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24
arch/x86/kernel/cpu/common.c
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@ -344,31 +344,15 @@ static void __init early_cpu_detect(void)
/*
* The NOPL instruction is supposed to exist on all CPUs with
* family >= 6, unfortunately, that's not true in practice because
* family >= 6; unfortunately, that's not true in practice because
* of early VIA chips and (more importantly) broken virtualizers that
* are not easy to detect. Hence, probe for it based on first
* principles.
* are not easy to detect. In the latter case it doesn't even *fail*
* reliably, so probing for it doesn't even work. Disable it completely
* unless we can find a reliable way to detect all the broken cases.
*/
static void __cpuinit detect_nopl(struct cpuinfo_x86 *c)
{
const u32 nopl_signature = 0x888c53b1; /* Random number */
u32 has_nopl = nopl_signature;
clear_cpu_cap(c, X86_FEATURE_NOPL);
if (c->x86 >= 6) {
asm volatile("\n"
"1: .byte 0x0f,0x1f,0xc0\n" /* nopl %eax */
"2:\n"
" .section .fixup,\"ax\"\n"
"3: xor %0,%0\n"
" jmp 2b\n"
" .previous\n"
_ASM_EXTABLE(1b,3b)
: "+a" (has_nopl));
if (has_nopl == nopl_signature)
set_cpu_cap(c, X86_FEATURE_NOPL);
}
}
static void __cpuinit generic_identify(struct cpuinfo_x86 *c)