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Subject[PATCH 3/4] x86, head_32: Remove CPUID detection from default_entry
Date
From: Borislav Petkov <bp@suse.de>

We do that once earlier now and cache it into boot_cpu_data.cpuid_level
so no need for the EFLAGS.ID toggling dance anymore.

Signed-off-by: Borislav Petkov <bp@suse.de>
---
arch/x86/kernel/head_32.S | 40 +++++++---------------------------------
1 file changed, 7 insertions(+), 33 deletions(-)

diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
index ce6b557017f4..0dba3598cf02 100644
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -334,25 +334,14 @@ default_entry:
movl %eax,%cr0

/*
- * New page tables may be in 4Mbyte page mode and may
- * be using the global pages.
+ * 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.
+ * NOTE! If we are on a 486 we may have no cr4 at all! Specifically, cr4 exists
+ * if and only if CPUID exists (which has been checked above) and has flags
+ * other than the FPU flag set.
*/
- movl $X86_EFLAGS_ID,%ecx
- pushl %ecx
- popfl
- pushfl
- popl %eax
- pushl $0
- popfl
- pushfl
- popl %edx
- xorl %edx,%eax
- testl %ecx,%eax
- jz 6f # No ID flag = no CPUID = no CR4
+ cmpl $-1, pa(X86_CPUID)
+ je 6f # No CPUID = no CR4

movl $1,%eax
cpuid
@@ -389,7 +378,6 @@ default_entry:
btsl $_EFER_NX, %eax
/* Make changes effective */
wrmsr
-
6:

/*
@@ -417,21 +405,7 @@ default_entry:
call *%eax
1:

-/*
- * Check if it is 486
- */
- movl $-1,X86_CPUID # -1 for no CPUID initially
- movb $4,X86 # at least 486
- pushfl # push EFLAGS
- popl %eax # get EFLAGS
- movl %eax,%ecx # save original EFLAGS
- xorl $0x200000,%eax # flip ID bit in EFLAGS
- pushl %eax # copy to EFLAGS
- popfl # set EFLAGS
- pushfl # get new EFLAGS
- popl %eax # put it in eax
- xorl %ecx,%eax # change in flags
- testl $0x200000,%eax # check if ID bit changed
+ cmpl $-1,X86_CPUID
je is486

/* get vendor info */
--
1.8.1.2.422.g08c0e7f


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