[PATCH v3 20/20] powerpc/mm: Add speculative page fault

[Laurent Dufour]

This patch enable the speculative page fault on the PowerPC
architecture.

This will try a speculative page fault without holding the mmap_sem,
if it returns with VM_FAULT_RETRY, the mmap_sem is acquired and the
traditional page fault processing is done.

Support is only provide for BOOK3S_64 currently because:
- require CONFIG_PPC_STD_MMU because checks done in
  set_access_flags_filter()
- require BOOK3S because we can't support for book3e_hugetlb_preload()
  called by update_mmu_cache()

Signed-off-by: Laurent Dufour <lduf...@linux.vnet.ibm.com>
---
 arch/powerpc/include/asm/book3s/64/pgtable.h |  5 +++++
 arch/powerpc/mm/fault.c                      | 15 +++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h 
b/arch/powerpc/include/asm/book3s/64/pgtable.h
index b9aff515b4de..470203daf97e 100644
--- a/arch/powerpc/include/asm/book3s/64/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
@@ -314,6 +314,11 @@ extern unsigned long pci_io_base;
 /* Advertise support for _PAGE_SPECIAL */
 #define __HAVE_ARCH_PTE_SPECIAL
 
+/* Advertise that we call the Speculative Page Fault handler */
+#if defined(CONFIG_PPC_BOOK3S_64)
+#define __HAVE_ARCH_CALL_SPF
+#endif
+
 #ifndef __ASSEMBLY__
 
 /*
diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 4797d08581ce..97c7de242627 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -442,6 +442,20 @@ static int __do_page_fault(struct pt_regs *regs, unsigned 
long address,
        if (is_exec)
                flags |= FAULT_FLAG_INSTRUCTION;
 
+#if defined(__HAVE_ARCH_CALL_SPF)
+       if (is_user) {
+               /* let's try a speculative page fault without grabbing the
+                * mmap_sem.
+                */
+               fault = handle_speculative_fault(mm, address, flags);
+               if (!(fault & VM_FAULT_RETRY)) {
+                       perf_sw_event(PERF_COUNT_SW_SPF, 1,
+                                     regs, address);
+                       goto done;
+               }
+       }
+#endif /* defined(__HAVE_ARCH_CALL_SPF) */
+
        /* When running in the kernel we expect faults to occur only to
         * addresses in user space.  All other faults represent errors in the
         * kernel and should generate an OOPS.  Unfortunately, in the case of an
@@ -526,6 +540,7 @@ static int __do_page_fault(struct pt_regs *regs, unsigned 
long address,
 
        up_read(&current->mm->mmap_sem);
 
+done:
        if (unlikely(fault & VM_FAULT_ERROR))
                return mm_fault_error(regs, address, fault);
 
-- 
2.7.4