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SubjectRe: Dynamic nop selection breaks boot on Geode LX
From: Borislav Petkov <bp@alien8.de>
Date: Sun, Oct 03, 2010 at 07:50:13AM +0200

> Maybe on a Geode jmp label should use the 2-byte jmp + 3 1-byte nops
> unconditionally after adding a synthetic CPUID flag in init_amd_k6(), in
> the Geode part.

Maybe something like the following? (only tested in kvm)

--
diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index 220e2ea..e2ef56c 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -89,7 +89,7 @@
#define X86_FEATURE_LFENCE_RDTSC (3*32+18) /* "" Lfence synchronizes RDTSC */
#define X86_FEATURE_11AP (3*32+19) /* "" Bad local APIC aka 11AP */
#define X86_FEATURE_NOPL (3*32+20) /* The NOPL (0F 1F) instructions */
- /* 21 available, was AMD_C1E */
+#define X86_FEATURE_NO_NOPL (3*32+21) /* "" Missing NOPL (e.g. Geode LX) */
#define X86_FEATURE_XTOPOLOGY (3*32+22) /* cpu topology enum extensions */
#define X86_FEATURE_TSC_RELIABLE (3*32+23) /* TSC is known to be reliable */
#define X86_FEATURE_NONSTOP_TSC (3*32+24) /* TSC does not stop in C states */
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index cb0e6d3..3e1fa13 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -666,6 +666,9 @@ void __init arch_init_ideal_nop5(void)
*
* TODO: check the cpuid to determine the best nop.
*/
+ if (boot_cpu_has(X86_FEATURE_NO_NOPL))
+ goto early_done;
+
asm volatile (
"ftrace_test_jmp:"
"jmp ftrace_test_p6nop\n"
@@ -688,6 +691,7 @@ void __init arch_init_ideal_nop5(void)
_ASM_EXTABLE(ftrace_test_nop5, 3b)
: "=r"(faulted) : "0" (faulted));

+early_done:
switch (faulted) {
case 0:
pr_info("converting mcount calls to 0f 1f 44 00 00\n");
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 7b875fd..d1e5cf4 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -139,7 +139,7 @@ static void __cpuinit init_amd_k6(struct cpuinfo_x86 *c)

if (c->x86_model == 10) {
/* AMD Geode LX is model 10 */
- /* placeholder for any needed mods */
+ set_cpu_cap(c, X86_FEATURE_NO_NOPL);
return;
}
}
--
Regards/Gruss,
Boris.


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