x86: fix setup code crashes on my old 486 box

commit 7b27718bdb1b70166383dec91391df5534d449ee upstream

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.

Alan Cox observed that it's available since the Pentium II, so cpuid
levels 4 and 5 can be excluded altogether.

H. Peter Anvin cleaned up the code some more:

> 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?

which, with a small modification to fix a build error with it the
resulting kernel boots on my machine.

Signed-off-by: Joerg Roedel <joro@8bytes.org>
Signed-off-by: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/arch/x86/boot/boot.h b/arch/x86/boot/boot.h
index 7822a4983da2376a8b4297cf3bad80a3519c717e..4f199c1f8186fc829887583374456a69f0250713 100644 (file)
--- a/arch/x86/boot/boot.h
+++ b/arch/x86/boot/boot.h
@@ -27,6 +27,8 @@
 #include <asm/boot.h>
 #include <asm/setup.h>
 
+#define NCAPINTS   8
+
 /* Useful macros */
 #define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))
 
@@ -244,6 +246,12 @@ 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 769065bd23d776dc6c96a171f87b7071fd3719a6..b93b194bb53305b5abd87c1b936e41615288009a 100644 (file)
--- a/arch/x86/boot/cpucheck.c
+++ b/arch/x86/boot/cpucheck.c
@@ -32,13 +32,7 @@
 #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 7828da5cfd07475376c7d4d3fc95282334b60a3d..3d86d659021bea0176d54f7aa2e06f2d6b9c8b87 100644 (file)
--- a/arch/x86/boot/main.c
+++ b/arch/x86/boot/main.c
@@ -75,6 +75,10 @@ static void keyboard_set_repeat(void)
  */
 static void query_ist(void)
 {
+       /* Some 486 BIOSes apparently crash on this call */
+       if (cpu.level < 6)
+               return;
+
        asm("int $0x15"
            : "=a" (boot_params.ist_info.signature),
              "=b" (boot_params.ist_info.command),