Revert "x86/mm: Set IBPB upon context switch"

CVE-2017-5753 (revert embargoed)
CVE-2017-5715 (revert embargoed)

This reverts commit 49bb7a3c.
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

arch/x86/mm/tlb.c

@@ -14,7 +14,6 @@
 #include <asm/apic.h>
 #include <asm/uv/uv.h>
 #include <asm/kaiser.h>
-#include <asm/microcode.h>
 
 /*
  *	Smarter SMP flushing macros.
@@ -140,9 +139,6 @@ void switch_mm(struct mm_struct *prev, struct mm_struct *next,
 		/* Stop flush ipis for the previous mm */
 		cpumask_clear_cpu(cpu, mm_cpumask(prev));
 
-		if (boot_cpu_has(X86_FEATURE_SPEC_CTRL))
-			native_wrmsrl(MSR_IA32_PRED_CMD, FEATURE_SET_IBPB);
-
 		/* Load per-mm CR4 state */
 		load_mm_cr4(next);