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Subject[PATCH v3 20/20] powerpc/mm: Add speculative page fault
Date
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 <ldufour@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
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