From: Borislav Petkov <bp@alien8.de>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: X86 ML <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
Borislav Petkov <bp@suse.de>
Subject: [PATCH 2/4] x86: Detect CPUID support early at boot
Date: Mon, 11 Feb 2013 15:22:16 +0100 [thread overview]
Message-ID: <1360592538-10643-3-git-send-email-bp@alien8.de> (raw)
In-Reply-To: <1360592538-10643-1-git-send-email-bp@alien8.de>
From: Borislav Petkov <bp@suse.de>
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>
---
arch/x86/kernel/head_32.S | 50 +++++++++++++++++++++++------------------------
1 file changed, 25 insertions(+), 25 deletions(-)
diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
index f4d919e2cd2b..73e084a6d2c5 100644
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -318,30 +318,39 @@ default_entry:
movl %eax,%cr0
/*
- * New page tables may be in 4Mbyte page mode and may
- * be using the global pages.
+ * 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.
+ */
+ 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.
+ * 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
- pushfl
- popl %eax
- pushl $0
- popfl
+ 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
@@ -389,14 +398,6 @@ default_entry:
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.
*/
@@ -472,7 +473,6 @@ 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)
--
1.8.1.3.535.ga923c31
next prev parent reply other threads:[~2013-02-11 14:22 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-11 14:22 [PATCH 0/4 -v3] x86, head_32: Some cleanups Borislav Petkov
2013-02-11 14:22 ` [PATCH 1/4] x86, head_32: Remove i386 pieces Borislav Petkov
2013-02-13 0:07 ` [tip:x86/asm] " tip-bot for Borislav Petkov
2013-02-11 14:22 ` Borislav Petkov [this message]
2013-02-13 0:09 ` [tip:x86/asm] x86: Detect CPUID support early at boot tip-bot for Borislav Petkov
2013-02-11 14:22 ` [PATCH 3/4] x86, head_32: Remove second CPUID detection from default_entry Borislav Petkov
2013-02-11 15:49 ` H. Peter Anvin
2013-02-11 17:15 ` Borislav Petkov
2013-02-11 17:21 ` H. Peter Anvin
2013-02-13 0:10 ` [tip:x86/asm] " tip-bot for Borislav Petkov
2013-02-11 14:22 ` [PATCH 4/4] x86, head_32: Give the 6 label a real name Borislav Petkov
2013-02-13 0:11 ` [tip:x86/asm] " tip-bot for Borislav Petkov
2013-02-11 16:56 ` [PATCH 0/4 -v3] x86, head_32: Some cleanups H. Peter Anvin
-- strict thread matches above, loose matches on Subject: below --
2013-02-03 16:14 [PATCH 0/4] " Borislav Petkov
2013-02-03 16:14 ` [PATCH 2/4] x86: Detect CPUID support early at boot Borislav Petkov
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