linux-kernel - Re: Dynamic nop selection breaks boot on Geode LX

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Date:	Sun, 3 Oct 2010 11:26:12 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Daniel Drake <dsd@...top.org>
Cc:	jbaron@...hat.com, Andres Salomon <dilinger@...ued.net>,
	Chris Ball <cjb@...top.org>, linux-kernel@...r.kernel.org,
	rostedt@...dmis.org
Subject: Re: Dynamic nop selection breaks boot on Geode LX

From: Borislav Petkov <bp@...en8.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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