linux-kernel - [PATCH 2/7] x86/enter: MACROS to set/clear IBRS

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Date:   Thu,  4 Jan 2018 09:56:43 -0800
From:   Tim Chen <tim.c.chen@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg KH <gregkh@...uxfoundation.org>
Cc:     Tim Chen <tim.c.chen@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@...el.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 2/7] x86/enter: MACROS to set/clear IBRS

Create macros to control IBRS.  Use these macros to enable IBRS on kernel entry
paths and disable IBRS on kernel exit paths.

The registers rax, rcx and rdx are touched when controlling IBRS
so they need to be saved when they can't be clobbered.

Signed-off-by: Tim Chen <tim.c.chen@...ux.intel.com>
---
 arch/x86/include/asm/spec_ctrl.h | 80 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 80 insertions(+)
 create mode 100644 arch/x86/include/asm/spec_ctrl.h

diff --git a/arch/x86/include/asm/spec_ctrl.h b/arch/x86/include/asm/spec_ctrl.h
new file mode 100644
index 0000000..16fc4f58
--- /dev/null
+++ b/arch/x86/include/asm/spec_ctrl.h
@@ -0,0 +1,80 @@
+#ifndef _ASM_X86_SPEC_CTRL_H
+#define _ASM_X86_SPEC_CTRL_H
+
+#include <linux/stringify.h>
+#include <asm/msr-index.h>
+#include <asm/cpufeatures.h>
+#include <asm/alternative-asm.h>
+
+#ifdef __ASSEMBLY__
+
+.macro PUSH_MSR_REGS
+	pushq %rax
+	pushq %rcx
+	pushq %rdx
+.endm
+
+.macro POP_MSR_REGS
+	popq %rdx
+	popq %rcx
+	popq %rax;
+.endm
+
+.macro WRMSR_ASM msr_nr:req eax_val:req
+	movl \msr_nr, %ecx
+	movl $0, %edx
+	movl \eax_val, %eax
+.endm
+
+.macro ENABLE_IBRS
+	ALTERNATIVE "jmp 10f", "", X86_FEATURE_SPEC_CTRL
+	PUSH_MSR_REGS
+	WRMSR_ASM $MSR_IA32_SPEC_CTRL, $SPEC_CTRL_FEATURE_ENABLE_IBRS
+	POP_MSR_REGS
+10:
+.endm
+
+.macro DISABLE_IBRS
+	ALTERNATIVE "jmp 10f", "", X86_FEATURE_SPEC_CTRL
+	PUSH_MSR_REGS
+	WRMSR_ASM $MSR_IA32_SPEC_CTRL, $SPEC_CTRL_FEATURE_DISABLE_IBRS
+	POP_MSR_REGS
+10:
+.endm
+
+.macro ENABLE_IBRS_CLOBBER
+	ALTERNATIVE "jmp 10f", "", X86_FEATURE_SPEC_CTRL
+	WRMSR_ASM $MSR_IA32_SPEC_CTRL, $SPEC_CTRL_FEATURE_ENABLE_IBRS
+10:
+.endm
+
+.macro DISABLE_IBRS_CLOBBER
+	ALTERNATIVE "jmp 10f", "", X86_FEATURE_SPEC_CTRL
+	WRMSR_ASM $MSR_IA32_SPEC_CTRL, $SPEC_CTRL_FEATURE_DISABLE_IBRS
+10:
+.endm
+
+.macro ENABLE_IBRS_SAVE_AND_CLOBBER save_reg:req
+	ALTERNATIVE "jmp 10f", "", X86_FEATURE_SPEC_CTRL
+	movl	$MSR_IA32_SPEC_CTRL, %ecx
+	rdmsr
+	movl	%eax, \save_reg
+
+	movl	$0, %edx
+	movl	$SPEC_CTRL_FEATURE_ENABLE_IBRS, %eax
+	wrmsr
+10:
+.endm
+
+.macro RESTORE_IBRS_CLOBBER save_reg:req
+	ALTERNATIVE "jmp 10f", "", X86_FEATURE_SPEC_CTRL
+	/* Set IBRS to the value saved in the save_reg */
+	movl    $MSR_IA32_SPEC_CTRL, %ecx
+        movl    $0, %edx
+	movl    \save_reg, %eax
+	wrmsr
+10:
+.endm
+
+#endif /* __ASSEMBLY__ */
+#endif /* _ASM_X86_SPEC_CTRL_H */
-- 
2.9.4