From: Borislav Petkov <[email protected]> We detect CPUID function support on the boot 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 <[email protected]> --- arch/x86/kernel/head_32.S | 36 +++++++++++++++++++++++++++++------- 1 file changed, 29 insertions(+), 7 deletions(-) diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S index a9c5cc851285..ce6b557017f4 100644 --- a/arch/x86/kernel/head_32.S +++ b/arch/x86/kernel/head_32.S @@ -29,16 +29,16 @@ /* * References to members of the new_cpu_data structure. */ - #define X86 new_cpu_data+CPUINFO_x86 #define X86_VENDOR new_cpu_data+CPUINFO_x86_vendor #define X86_MODEL new_cpu_data+CPUINFO_x86_model #define X86_MASK new_cpu_data+CPUINFO_x86_mask #define X86_HARD_MATH new_cpu_data+CPUINFO_hard_math -#define X86_CPUID new_cpu_data+CPUINFO_cpuid_level #define X86_CAPABILITY new_cpu_data+CPUINFO_x86_capability #define X86_VENDOR_ID new_cpu_data+CPUINFO_x86_vendor_id +#define X86_CPUID boot_cpu_data+CPUINFO_cpuid_level + /* * This is how much memory in addition to the memory covered up to * and including _end we need mapped initially. @@ -263,6 +263,33 @@ subarch_entries: num_subarch_entries = (. - subarch_entries) / 4 .previous #else + +/* + * Initialize EFLAGS. Some BIOS's leave bits like NT set. This would confuse the + * debugger if this code is traced. + */ + pushl $0 + popfl + +/* + * Check whether this CPU supports CPUID, and, if so, save the highest standard + * CPUID function number for later. + */ + movl $X86_EFLAGS_ID,%ecx /* EFLAGS.ID */ + pushl %ecx + popfl /* set EFLAGS=ID */ + pushfl /* get EFLAGS */ + popl %eax + xorl %ecx,%eax + jnz 1f /* hw disallowed setting of ID bit */ + + xorl %eax,%eax + cpuid + movl %eax,pa(X86_CPUID) /* save largest std CPUID function */ + jmp default_entry + +1: + movl $-1,pa(X86_CPUID) jmp default_entry #endif /* CONFIG_PARAVIRT */ @@ -377,11 +404,6 @@ 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 -- 1.8.1.2.422.g08c0e7f -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
