Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 fixes from Thomas Gleixner:
 "Hopefully the last round of fixes for 3.19

   - regression fix for the LDT changes
   - regression fix for XEN interrupt handling caused by the APIC
     changes
   - regression fixes for the PAT changes
   - last minute fixes for new the MPX support
   - regression fix for 32bit UP
   - fix for a long standing relocation issue on 64bit tagged for stable
   - functional fix for the Hyper-V clocksource tagged for stable
   - downgrade of a pr_err which tends to confuse users

  Looks a bit on the large side, but almost half of it are valuable
  comments"

* 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/tsc: Change Fast TSC calibration failed from error to info
  x86/apic: Re-enable PCI_MSI support for non-SMP X86_32
  x86, mm: Change cachemode exports to non-gpl
  x86, tls: Interpret an all-zero struct user_desc as "no segment"
  x86, tls, ldt: Stop checking lm in LDT_empty
  x86, mpx: Strictly enforce empty prctl() args
  x86, mpx: Fix potential performance issue on unmaps
  x86, mpx: Explicitly disable 32-bit MPX support on 64-bit kernels
  x86, hyperv: Mark the Hyper-V clocksource as being continuous
  x86: Don't rely on VMWare emulating PAT MSR correctly
  x86, irq: Properly tag virtualization entry in /proc/interrupts
  x86, boot: Skip relocs when load address unchanged
  x86/xen: Override ACPI IRQ management callback __acpi_unregister_gsi
  ACPI: pci: Do not clear pci_dev->irq in acpi_pci_irq_disable()
  x86/xen: Treat SCI interrupt as normal GSI interrupt

1 files changed, 19 insertions, 1 deletions

diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index 40269a2bf6f..4b75d591eb5 100644
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -130,7 +130,25 @@ static inline void arch_bprm_mm_init(struct mm_struct *mm,
 static inline void arch_unmap(struct mm_struct *mm, struct vm_area_struct *vma,
 			      unsigned long start, unsigned long end)
 {
-	mpx_notify_unmap(mm, vma, start, end);
+	/*
+	 * mpx_notify_unmap() goes and reads a rarely-hot
+	 * cacheline in the mm_struct.  That can be expensive
+	 * enough to be seen in profiles.
+	 *
+	 * The mpx_notify_unmap() call and its contents have been
+	 * observed to affect munmap() performance on hardware
+	 * where MPX is not present.
+	 *
+	 * The unlikely() optimizes for the fast case: no MPX
+	 * in the CPU, or no MPX use in the process.  Even if
+	 * we get this wrong (in the unlikely event that MPX
+	 * is widely enabled on some system) the overhead of
+	 * MPX itself (reading bounds tables) is expected to
+	 * overwhelm the overhead of getting this unlikely()
+	 * consistently wrong.
+	 */
+	if (unlikely(cpu_feature_enabled(X86_FEATURE_MPX)))
+		mpx_notify_unmap(mm, vma, start, end);
 }
 
 #endif /* _ASM_X86_MMU_CONTEXT_H */