[PATCH] i386: Verify important CPUID bits in real mode

Check some CPUID bits that are needed for compiler generated early in boot.
When the system is still in real mode before changing the VESA BIOS mode
it is possible to still display an visible error message on the screen.

Similar to x86-64.

Includes cleanups from Eric Biederman

Signed-off-by: Andi Kleen <ak@suse.de>

3 files changed, 102 insertions, 2 deletions

diff --git a/arch/i386/Kconfig.cpu b/arch/i386/Kconfig.cpu
index b1af9f5..dce6124 100644
--- a/arch/i386/Kconfig.cpu
+++ b/arch/i386/Kconfig.cpu
@@ -240,14 +240,19 @@ config X86_L1_CACHE_SHIFT
 	default "5" if MWINCHIP3D || MWINCHIP2 || MWINCHIPC6 || MCRUSOE || MEFFICEON || MCYRIXIII || MK6 || MPENTIUMIII || MPENTIUMII || M686 || M586MMX || M586TSC || M586 || MVIAC3_2 || MGEODE_LX
 	default "6" if MK7 || MK8 || MPENTIUMM || MCORE2 || MVIAC7
 
+config X86_XADD
+	bool
+	depends on !M386
+	default y
+
 config RWSEM_GENERIC_SPINLOCK
 	bool
-	depends on M386
+	depends on !X86_XADD
 	default y
 
 config RWSEM_XCHGADD_ALGORITHM
 	bool
-	depends on !M386
+	depends on X86_XADD
 	default y
 
 config ARCH_HAS_ILOG2_U32
@@ -331,3 +336,16 @@ config X86_TSC
 	bool
 	depends on (MWINCHIP3D || MWINCHIP2 || MCRUSOE || MEFFICEON || MCYRIXIII || MK7 || MK6 || MPENTIUM4 || MPENTIUMM || MPENTIUMIII || MPENTIUMII || M686 || M586MMX || M586TSC || MK8 || MVIAC3_2 || MVIAC7 || MGEODEGX1 || MGEODE_LX || MCORE2) && !X86_NUMAQ
 	default y
+
+# this should be set for all -march=.. options where the compiler
+# generates cmov.
+config X86_CMOV
+	bool
+	depends on (MK7 || MPENTIUM4 || MPENTIUMM || MPENTIUMIII || MPENTIUMII || M686 || MVIAC3_2 || MVIAC7)
+	default y
+
+config X86_MINIMUM_CPU_MODEL
+	int
+	default "4" if X86_XADD || X86_CMPXCHG || X86_BSWAP
+	default "0"
+
diff --git a/arch/i386/boot/setup.S b/arch/i386/boot/setup.S
index b74b7f4..f8b3b9c 100644
--- a/arch/i386/boot/setup.S
+++ b/arch/i386/boot/setup.S
@@ -302,7 +302,24 @@ good_sig:
 
 loader_panic_mess: .string "Wrong loader, giving up..."
 
+# check minimum cpuid
+# we do this here because it is the last place we can actually
+# show a user visible error message. Later the video modus
+# might be already messed up.
 loader_ok:
+	call verify_cpu
+	testl  %eax,%eax
+	jz	cpu_ok
+	lea	cpu_panic_mess,%si
+	call	prtstr
+1:	jmp	1b
+
+cpu_panic_mess:
+	.asciz  "PANIC: CPU too old for this kernel."
+
+#include "../kernel/verify_cpu.S"
+
+cpu_ok:
 # Get memory size (extended mem, kB)
 
 	xorl	%eax, %eax
diff --git a/arch/i386/kernel/verify_cpu.S b/arch/i386/kernel/verify_cpu.S
new file mode 100644
index 0000000..e51a869
--- /dev/null
+++ b/arch/i386/kernel/verify_cpu.S
@@ -0,0 +1,65 @@
+/* Check if CPU has some minimum CPUID bits
+   This runs in 16bit mode so that the caller can still use the BIOS
+   to output errors on the screen */
+#include <asm/cpufeature.h>
+
+verify_cpu:
+	pushfl				# Save caller passed flags
+	pushl	$0			# Kill any dangerous flags
+	popfl
+
+#if CONFIG_X86_MINIMUM_CPU_MODEL >= 4
+	pushfl
+	orl	$(1<<18),(%esp)		# try setting AC
+	popfl
+	pushfl
+	popl    %eax
+	testl	$(1<<18),%eax
+	jz	bad
+#endif
+#if REQUIRED_MASK1 != 0
+	pushfl				# standard way to check for cpuid
+	popl	%eax
+	movl	%eax,%ebx
+	xorl	$0x200000,%eax
+	pushl	%eax
+	popfl
+	pushfl
+	popl	%eax
+	cmpl	%eax,%ebx
+	pushfl				# standard way to check for cpuid
+	popl	%eax
+	movl	%eax,%ebx
+	xorl	$0x200000,%eax
+	pushl	%eax
+	popfl
+	pushfl
+	popl	%eax
+	cmpl	%eax,%ebx
+	jz	bad			# REQUIRED_MASK1 != 0 requires CPUID
+
+	movl	$0x0,%eax		# See if cpuid 1 is implemented
+	cpuid
+	cmpl	$0x1,%eax
+	jb	bad			# no cpuid 1
+
+	movl    $0x1,%eax		# Does the cpu have what it takes
+	cpuid
+
+#if CONFIG_X86_MINIMUM_CPU_MODEL > 4
+#error	add proper model checking here
+#endif
+
+	andl	$REQUIRED_MASK1,%edx
+	xorl	$REQUIRED_MASK1,%edx
+	jnz	bad
+#endif /* REQUIRED_MASK1 */
+
+	popfl
+	xor	%eax,%eax
+	ret
+
+bad:
+	popfl
+	movl	$1,%eax
+	ret