Re: Setup code crashes my old 486 box

["H. Peter Anvin" <hpa@zytor.com>]

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Joerg Roedel wrote:
> Hello,
> 
> yesterday I tried to reactivate my old 486 box and wanted to install a
> current Linux with latest kernel on it. But it turned out that the
> latest kernel does not boot because the machine crashes early in the
> setup code.
> After some debugging it turned out that the problem is the query_ist()
> function. If this interrupt with that function is called the machine
> simply locks up. It looks like a BIOS bug. Looking for a workaround for
> this problem I wrote the attached patch. It checks for the CPUID
> instruction and if it is not implemented it does not call the speedstep
> BIOS function. As far as I know speedstep should be available since some
> Pentium earliest.
> Is this an acceptable workaround or is there a better one for this?
> 
> Regards,
> 
> Joerg

Right in concept, but I dislike the implementation (duplication of the 
CPU detect code we already have).  Could you try this patch and see if 
it works for you?

	-hpa

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diff --git a/arch/x86/boot/boot.h b/arch/x86/boot/boot.h
index a34b998..9ce8d29 100644
--- a/arch/x86/boot/boot.h
+++ b/arch/x86/boot/boot.h
@@ -242,6 +242,12 @@ int cmdline_find_option(const char *option, char *buffer, int bufsize);
 int cmdline_find_option_bool(const char *option);
 
 /* cpu.c, cpucheck.c */
+struct cpu_features {
+	int level;		/* Family, or 64 for x86-64 */
+	int model;
+	u32 flags[NCAPINTS];
+};
+extern struct cpu_features cpu;
 int check_cpu(int *cpu_level_ptr, int *req_level_ptr, u32 **err_flags_ptr);
 int validate_cpu(void);
 
diff --git a/arch/x86/boot/cpucheck.c b/arch/x86/boot/cpucheck.c
index 7804389..c1ce030 100644
--- a/arch/x86/boot/cpucheck.c
+++ b/arch/x86/boot/cpucheck.c
@@ -30,13 +30,7 @@
 #include <asm/required-features.h>
 #include <asm/msr-index.h>
 
-struct cpu_features {
-	int level;		/* Family, or 64 for x86-64 */
-	int model;
-	u32 flags[NCAPINTS];
-};
-
-static struct cpu_features cpu;
+struct cpu_features cpu;
 static u32 cpu_vendor[3];
 static u32 err_flags[NCAPINTS];
 
diff --git a/arch/x86/boot/main.c b/arch/x86/boot/main.c
index 2296164..9b04773 100644
--- a/arch/x86/boot/main.c
+++ b/arch/x86/boot/main.c
@@ -73,6 +73,10 @@ static void keyboard_set_repeat(void)
  */
 static void query_ist(void)
 {
+	/* Some 486 BIOSes apparently crash on this call */
+	if (cpu.level < 5)
+		return;
+
 	asm("int $0x15"
 	    : "=a" (boot_params.ist_info.signature),
 	      "=b" (boot_params.ist_info.command),