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x86: Detect CPUID support early at boot

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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: Borislav Petkov <bp@suse.de>
Link: http://lkml.kernel.org/r/1360592538-10643-3-git-send-email-bp@alien8.de
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This commit is contained in:
Borislav Petkov 2013-02-11 15:22:16 +01:00 committed by H. Peter Anvin
parent 166df91daf
commit 9efb58de91
1 changed files with 26 additions and 26 deletions
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52
arch/x86/kernel/head_32.S
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@ -307,30 +307,39 @@ default_entry:
movl %eax,%cr0
/*
* 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!
* Specifically, cr4 exists if and only if CPUID exists
* and has flags other than the FPU flag set.
* We want to start out with EFLAGS unambiguously cleared. Some BIOSes leave
* 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.
*/
movl $X86_EFLAGS_ID,%ecx
pushl %ecx
popfl
pushfl
popl %eax
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! Specifically, cr4 exists
* if and only if CPUID exists and has flags other than the FPU flag set.
*/
movl $-1,pa(X86_CPUID) # preset CPUID level
movl $X86_EFLAGS_ID,%ecx
pushl %ecx
popfl # set EFLAGS=ID
pushfl
popl %edx
xorl %edx,%eax
testl %ecx,%eax
jz 6f # No ID flag = no CPUID = no CR4
popl %eax # get EFLAGS
testl $X86_EFLAGS_ID,%eax # did EFLAGS.ID remained set?
jz 6f # hw disallowed setting of ID bit
# which means no CPUID and no CR4
xorl %eax,%eax
cpuid
movl %eax,pa(X86_CPUID) # save largest std CPUID function
movl $1,%eax
cpuid
andl $~1,%edx # Ignore CPUID.FPU
jz 6f # No flags or only CPUID.FPU = no CR4
andl $~1,%edx # Ignore CPUID.FPU
jz 6f # No flags or only CPUID.FPU = no CR4
movl pa(mmu_cr4_features),%eax
movl %eax,%cr4
@ -377,14 +386,6 @@ default_entry:
/* Shift the stack pointer to a virtual address */
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
* 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
lldt %ax
cld # gcc2 wants the direction flag cleared at all times
pushl $0 # fake return address for unwinder
jmp *(initial_code)