[PATCH] x86 boot time check for cpu features

[PATCH] x86 boot time check for cpu features

[Brian Gerst]

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This patch allows the real mode setup code to check for required
features (such as cmov, pae, etc.) that would normally just cause the
boot process to silently hang.  Tested with a K6-2 (no cmov) and an
Athlon (has cmov), needs testing on a CPU without cpuid.

-- 

						Brian Gerst

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diff -ur linux-2.4.0t10/arch/i386/boot/setup.S linux/arch/i386/boot/setup.S
--- linux-2.4.0t10/arch/i386/boot/setup.S	Tue Oct 31 17:06:34 2000
+++ linux/arch/i386/boot/setup.S	Thu Nov  2 21:04:01 2000
@@ -364,6 +364,55 @@
 	xorw	%bx, %bx
 	int	$0x16
 
+/* This is butt ugly, but it works. */
+#ifdef CONFIG_X86_CMOV
+# define REQD_CMOV	0x00008000
+#else
+# define REQD_CMOV	0
+#endif
+#ifdef CONFIG_X86_PAE
+# define REQD_PAE	0x00000040
+#else
+# define REQD_PAE	0
+#endif
+#define REQD_FLAGS REQD_CMOV|REQD_PAE
+
+#if REQD_FLAGS
+/*
+ * We must check this here while we can still get a message to the console
+ * because instructions for newer processors (ie. cmovcc) may be present
+ * in C code.
+ */
+	pushfl
+	popl	%eax
+	xorl	$0x200000, %eax			# check ID flag
+	pushl	%eax
+	popfl
+	pushfl
+	popl	%edx
+	xorl	%edx, %eax
+	testl	$0x200000, %eax
+	jnz	cpuid_fail
+	xorl	%eax, %eax
+	cpuid
+	cmpl 	$1, %eax
+	jb	cpuid_fail
+	movl	$1, %eax
+	cpuid
+	andl	$REQD_FLAGS, %edx
+	cmpl	$REQD_FLAGS, %edx
+	je	cpuid_pass
+cpuid_fail:
+	pushw	%cs
+	popw	%ds
+	lea	cpuid_fail_msg, %si
+	call	prtstr
+1:	jmp	1b
+cpuid_fail_msg:
+	.string	"Required CPU features are not present - compile kernel for the proper CPU type."
+cpuid_pass:
+#endif
+	
 # Check for video adapter and its parameters and allow the
 # user to browse video modes.
 	call	video				# NOTE: we need %ds pointing
diff -ur linux-2.4.0t10/arch/i386/config.in linux/arch/i386/config.in
--- linux-2.4.0t10/arch/i386/config.in	Tue Oct 31 17:06:34 2000
+++ linux/arch/i386/config.in	Thu Nov  2 18:53:59 2000
@@ -82,6 +82,7 @@
    define_bool CONFIG_X86_GOOD_APIC y
    define_bool CONFIG_X86_PGE y
    define_bool CONFIG_X86_USE_PPRO_CHECKSUM y
+   define_bool CONFIG_X86_CMOV y
 fi
 if [ "$CONFIG_M686FXSR" = "y" ]; then
    define_int  CONFIG_X86_L1_CACHE_SHIFT 5
@@ -91,6 +92,7 @@
    define_bool CONFIG_X86_USE_PPRO_CHECKSUM y
    define_bool CONFIG_X86_FXSR y
    define_bool CONFIG_X86_XMM y
+   define_bool CONFIG_X86_CMOV y
 fi
 if [ "$CONFIG_MK6" = "y" ]; then
    define_int  CONFIG_X86_L1_CACHE_SHIFT 5
@@ -105,6 +107,7 @@
    define_bool CONFIG_X86_USE_3DNOW y
    define_bool CONFIG_X86_PGE y
    define_bool CONFIG_X86_USE_PPRO_CHECKSUM y
+   define_bool CONFIG_X86_CMOV y
 fi
 if [ "$CONFIG_MCRUSOE" = "y" ]; then
    define_int  CONFIG_X86_L1_CACHE_SHIFT 5

Re: [PATCH] x86 boot time check for cpu features

[Alan Cox]

> +	lea	cpuid_fail_msg, %si
> +	call	prtstr
> +1:	jmp	1b
> +cpuid_fail_msg:
> +	.string	"Required CPU features are not present - compile kernel for the proper CPU type."
> +cpuid_pass:

Only one very minor suggestion

1:	hlt
	j 1b


Q:	are any of the things you test present in processors only after we
	do magic 'cpuid' enable invocations ?

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Re: [PATCH] x86 boot time check for cpu features

[Brian Gerst]

Alan Cox wrote:
> 
> > +     lea     cpuid_fail_msg, %si
> > +     call    prtstr
> > +1:   jmp     1b
> > +cpuid_fail_msg:
> > +     .string "Required CPU features are not present - compile kernel for the proper CPU type."
> > +cpuid_pass:
> 
> Only one very minor suggestion
> 
> 1:      hlt
>         j 1b
> 
> Q:      are any of the things you test present in processors only after we
>         do magic 'cpuid' enable invocations ?

AFAIK, none of the braindead chips have cmov instructions or PAE support
(only PentiumPro+ and Athlon do).  If someone can prove me wrong I'd
like to know.

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						Brian Gerst
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Re: [PATCH] x86 boot time check for cpu features

[Brian Gerst]

Alan Cox wrote:
> Q:      are any of the things you test present in processors only after we
>         do magic 'cpuid' enable invocations ?

Hmm, after a bit more investigation, it appears that the Cyrix MII
processors support cmov instructions, even though we currently don't
compile for that processor with -march=i686.  Please ignore this patch
until I can come up with something better.

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						Brian Gerst
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Re: [PATCH] x86 boot time check for cpu features

[Alan Cox]

> Alan Cox wrote:
> > Q:      are any of the things you test present in processors only after we
> >         do magic 'cpuid' enable invocations ?
> 
> Hmm, after a bit more investigation, it appears that the Cyrix MII
> processors support cmov instructions, even though we currently don't
> compile for that processor with -march=i686.  Please ignore this patch
> until I can come up with something better.

I believe the MII always has CPUID enabled. It was the older Cyrixes that did
not. DaveJ is the guru..

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Re: [PATCH] x86 boot time check for cpu features

[Brian Gerst]

Alan Cox wrote:
> 
> > Alan Cox wrote:
> > > Q:      are any of the things you test present in processors only after we
> > >         do magic 'cpuid' enable invocations ?
> >
> > Hmm, after a bit more investigation, it appears that the Cyrix MII
> > processors support cmov instructions, even though we currently don't
> > compile for that processor with -march=i686.  Please ignore this patch
> > until I can come up with something better.
> 
> I believe the MII always has CPUID enabled. It was the older Cyrixes that did
> not. DaveJ is the guru..

Well, according to comments in bugs.h, some broken BIOSes disable cpuid.

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					Brian Gerst
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Re: [PATCH] x86 boot time check for cpu features

[davej]

Alan Cox wrote..

> > Hmm, after a bit more investigation, it appears that the Cyrix MII
> > processors support cmov instructions, even though we currently don't
> > compile for that processor with -march=i686.  Please ignore this patch
> > until I can come up with something better.

> I believe the MII always has CPUID enabled. It was the older Cyrixes
> that did not.

That was my understanding also.

d.

-- 
| Dave Jones <davej@suse.de>  http://www.suse.de/~davej
| SuSE Labs

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Re: [PATCH] x86 boot time check for cpu features

[davej]

Brian Gerst wrote...
>> I believe the MII always has CPUID enabled. It was the older Cyrixes
>> that did not. DaveJ is the guru..
> Well, according to comments in bugs.h, some broken BIOSes disable cpuid.

That bug fix is for the earlier Cyrix 6x86 if I'm not mistaken.
The MII is a different monster.

d.

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| Dave Jones <davej@suse.de>  http://www.suse.de/~davej
| SuSE Labs

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Re: [PATCH] x86 boot time check for cpu features

[Brian Gerst]

davej@suse.de wrote:
> 
> Brian Gerst wrote...
> >> I believe the MII always has CPUID enabled. It was the older Cyrixes
> >> that did not. DaveJ is the guru..
> > Well, according to comments in bugs.h, some broken BIOSes disable cpuid.
> 
> That bug fix is for the earlier Cyrix 6x86 if I'm not mistaken.
> The MII is a different monster.

According to the docs on VIA's site, the MII's cpuid can still be turned
off, but it is on by default at reset.  I wouldn't trust the BIOS to not
screw it up.

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					Brian Gerst
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Re: [PATCH] x86 boot time check for cpu features

[davej]

On Fri, 3 Nov 2000, Brian Gerst wrote:

> > That bug fix is for the earlier Cyrix 6x86 if I'm not mistaken.
> > The MII is a different monster.
> According to the docs on VIA's site, the MII's cpuid can still be turned
> off, but it is on by default at reset.  I wouldn't trust the BIOS to not
> screw it up.

Err, what? If it's on by default...
A old BIOS that doesn't know about it won't switch it off.
A BIOS that does know about it will leave it (or maybe offer an option to
 disable it)

If neither of the above are true (Ie, a BIOS bug) and it's switched off
by the time Linux boots, I think we'd have heard about it by now, as MII
users would notice a lack of features.

regards,

Dave.

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| Dave Jones <davej@suse.de>  http://www.suse.de/~davej
| SuSE Labs

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