Commit-ID:  930ce1a7a55bc0eb8917f453ee22f1b6d67df5cd
Gitweb:     https://git.kernel.org/tip/930ce1a7a55bc0eb8917f453ee22f1b6d67df5cd
Author:     David Woodhouse <d...@amazon.co.uk>
AuthorDate: Sat, 10 Feb 2018 23:39:23 +0000
Committer:  Ingo Molnar <mi...@kernel.org>
CommitDate: Sun, 11 Feb 2018 11:24:15 +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 <d...@amazon.co.uk>
Cc: Andy Lutomirski <l...@kernel.org>
Cc: Arjan van de Ven <ar...@linux.intel.com>
Cc: Borislav Petkov <b...@alien8.de>
Cc: Dan Williams <dan.j.willi...@intel.com>
Cc: Dave Hansen <dave.han...@linux.intel.com>
Cc: David Woodhouse <dw...@infradead.org>
Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org>
Cc: Josh Poimboeuf <jpoim...@redhat.com>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: arjan.van.de....@intel.com
Cc: dave.han...@intel.com
Cc: jmatt...@google.com
Cc: karah...@amazon.de
Cc: k...@vger.kernel.org
Cc: pbonz...@redhat.com
Cc: rkrc...@redhat.com
Cc: sir...@amazon.de
Link: 
http://lkml.kernel.org/r/1518305967-31356-3-git-send-email-d...@amazon.co.uk
Signed-off-by: Ingo Molnar <mi...@kernel.org>
---
 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 4d57894..300cc15 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 513f960..99799fb 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 71949bf..61152aa 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
-
-void __ibp_barrier(void)
-{
-       __wrmsr(MSR_IA32_PRED_CMD, PRED_CMD_IBPB, 0);
-}
-EXPORT_SYMBOL_GPL(__ibp_barrier);

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