Revert "x86/speculation: Simplify indirect_branch_prediction_barrier()"

Web:        https://git.kernel.org/torvalds/c/f208820a321f9b23d77d7eed89945d862d62a3ed
Commit:     f208820a321f9b23d77d7eed89945d862d62a3ed
Parent:     d37fc6d360a404b208547ba112e7dabb6533c7fc
Refname:    refs/heads/master
Author:     David Woodhouse <[email protected]>
AuthorDate: Sat Feb 10 23:39:23 2018 +0000
Committer:  Ingo Molnar <[email protected]>
CommitDate: Tue Feb 13 08:59:00 2018 +0100

    Revert "x86/speculation: Simplify indirect_branch_prediction_barrier()"
    
    This reverts commit 64e16720ea0879f8ab4547e3b9758936d483909b.
    
    We cannot call C functions like that, without marking all the
    call-clobbered registers as, well, clobbered. We might have got away
    with it for now because the __ibp_barrier() function was *fairly*
    unlikely to actually use any other registers. But no. Just no.
    
    Signed-off-by: David Woodhouse <[email protected]>
    Cc: Andy Lutomirski <[email protected]>
    Cc: Arjan van de Ven <[email protected]>
    Cc: Borislav Petkov <[email protected]>
    Cc: Dan Williams <[email protected]>
    Cc: Dave Hansen <[email protected]>
    Cc: David Woodhouse <[email protected]>
    Cc: Greg Kroah-Hartman <[email protected]>
    Cc: Josh Poimboeuf <[email protected]>
    Cc: Linus Torvalds <[email protected]>
    Cc: Peter Zijlstra <[email protected]>
    Cc: Thomas Gleixner <[email protected]>
    Cc: [email protected]
    Cc: [email protected]
    Cc: [email protected]
    Cc: [email protected]
    Cc: [email protected]
    Cc: [email protected]
    Cc: [email protected]
    Cc: [email protected]
    Link: http://lkml.kernel.org/r/[email protected]
    Signed-off-by: Ingo Molnar <[email protected]>
---
 arch/x86/include/asm/nospec-branch.h | 13 +++++++++----
 arch/x86/include/asm/processor.h     |  3 ---
 arch/x86/kernel/cpu/bugs.c           |  6 ------
 3 files changed, 9 insertions(+), 13 deletions(-)

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 4d57894635f2..300cc159b4a0 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -164,10 +164,15 @@ static inline void vmexit_fill_RSB(void)
 
 static inline void indirect_branch_prediction_barrier(void)
 {
-	alternative_input("",
-			  "call __ibp_barrier",
-			  X86_FEATURE_USE_IBPB,
-			  ASM_NO_INPUT_CLOBBER("eax", "ecx", "edx", "memory"));
+	asm volatile(ALTERNATIVE("",
+				 "movl %[msr], %%ecx\n\t"
+				 "movl %[val], %%eax\n\t"
+				 "movl $0, %%edx\n\t"
+				 "wrmsr",
+				 X86_FEATURE_USE_IBPB)
+		     : : [msr] "i" (MSR_IA32_PRED_CMD),
+			 [val] "i" (PRED_CMD_IBPB)
+		     : "eax", "ecx", "edx", "memory");
 }
 
 #endif /* __ASSEMBLY__ */
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 513f9604c192..99799fbd0f7e 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -969,7 +969,4 @@ bool xen_set_default_idle(void);
 
 void stop_this_cpu(void *dummy);
 void df_debug(struct pt_regs *regs, long error_code);
-
-void __ibp_barrier(void);
-
 #endif /* _ASM_X86_PROCESSOR_H */
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 71949bf2de5a..61152aa53377 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -337,9 +337,3 @@ ssize_t cpu_show_spectre_v2(struct device *dev,
 		       spectre_v2_module_string());
 }
 #endif