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Commit 9efb58de authored by Borislav Petkov's avatar Borislav Petkov Committed by H. Peter Anvin
Browse files

x86: Detect CPUID support early at boot 



We detect CPUID function support on each CPU and save it for later use,
obviating the need to play the toggle EFLAGS.ID game every time. C code
is looking at ->cpuid_level anyway.

Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Link: http://lkml.kernel.org/r/1360592538-10643-3-git-send-email-bp@alien8.de


Signed-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
parent 166df91d

arch/x86/kernel/head_32.S

+25 −25
Original line number Original line Diff line number Diff line
@@ -307,25 +307,34 @@ default_entry: 
	movl %eax,%cr0

	movl %eax,%cr0





/*

/*

 *	New page tables may be in 4Mbyte page mode and may

 * We want to start out with EFLAGS unambiguously cleared. Some BIOSes leave

 *	be using the global pages. 

 * bits like NT set. This would confuse the debugger if this code is traced. So

 * initialize them properly now before switching to protected mode. That means

 * DF in particular (even though we have cleared it earlier after copying the

 * command line) because GCC expects it.

 */

	pushl $0

	popfl



/*

 * New page tables may be in 4Mbyte page mode and may be using the global pages.

 *

 *

 *	NOTE! If we are on a 486 we may have no cr4 at all!

 * NOTE! If we are on a 486 we may have no cr4 at all! Specifically, cr4 exists

 *	Specifically, cr4 exists if and only if CPUID exists

 * if and only if CPUID exists and has flags other than the FPU flag set.

 *	and has flags other than the FPU flag set.

 */

 */

	movl $-1,pa(X86_CPUID)		# preset CPUID level

	movl $X86_EFLAGS_ID,%ecx

	movl $X86_EFLAGS_ID,%ecx

	pushl %ecx

	pushl %ecx

	popfl

	popfl				# set EFLAGS=ID

	pushfl

	popl %eax

	pushl $0

	popfl

	pushfl

	pushfl

	popl %edx

	popl %eax			# get EFLAGS

	xorl %edx,%eax

	testl $X86_EFLAGS_ID,%eax	# did EFLAGS.ID remained set?

	testl %ecx,%eax

	jz 6f				# hw disallowed setting of ID bit

	jz 6f			# No ID flag = no CPUID = no CR4

					# which means no CPUID and no CR4



	xorl %eax,%eax

	cpuid

	movl %eax,pa(X86_CPUID)		# save largest std CPUID function





	movl $1,%eax

	movl $1,%eax

	cpuid

	cpuid
@@ -377,14 +386,6 @@ default_entry: 
	/* Shift the stack pointer to a virtual address */

	/* Shift the stack pointer to a virtual address */

	addl $__PAGE_OFFSET, %esp

	addl $__PAGE_OFFSET, %esp





/*

 * Initialize eflags.  Some BIOS's leave bits like NT set.  This would

 * confuse the debugger if this code is traced.

 * XXX - best to initialize before switching to protected mode.

 */

	pushl $0

	popfl



/*

/*

 * start system 32-bit setup. We need to re-do some of the things done

 * start system 32-bit setup. We need to re-do some of the things done

 * in 16-bit mode for the "real" operations.

 * in 16-bit mode for the "real" operations.
@@ -461,7 +462,6 @@ is486: movl $0x50022,%ecx # set AM, WP, NE and MP 
	xorl %eax,%eax			# Clear LDT

	xorl %eax,%eax			# Clear LDT

	lldt %ax

	lldt %ax





	cld			# gcc2 wants the direction flag cleared at all times

	pushl $0		# fake return address for unwinder

	pushl $0		# fake return address for unwinder

	jmp *(initial_code)

	jmp *(initial_code)