This patch enables the speculative page fault on the arm64
architecture.
I completed spf porting in 4.9. From the test result,
we can see app launching time improved by about 10% in average.
For the apps which have more than 50 threads, 15% or even more
improvement can be got.
Signed-off-by: Ganesh Mahendran <opensource.ganesh@xxxxxxxxx>
---
This patch is on top of Laurent's v10 spf
---
arch/arm64/mm/fault.c | 38 +++++++++++++++++++++++++++++++++++---
1 file changed, 35 insertions(+), 3 deletions(-)
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 4165485..e7992a3 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -322,11 +322,13 @@ static void do_bad_area(unsigned long addr, unsigned int esr, struct pt_regs *re
static int __do_page_fault(struct mm_struct *mm, unsigned long addr,
unsigned int mm_flags, unsigned long vm_flags,
- struct task_struct *tsk)
+ struct task_struct *tsk, struct vm_area_struct *vma)
{
- struct vm_area_struct *vma;
int fault;
+ if (!vma || !can_reuse_spf_vma(vma, addr))
+ vma = find_vma(mm, addr);
+
vma = find_vma(mm, addr);
fault = VM_FAULT_BADMAP;
if (unlikely(!vma))
@@ -371,6 +373,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
int fault, major = 0;
unsigned long vm_flags = VM_READ | VM_WRITE;
unsigned int mm_flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+ struct vm_area_struct *vma;
if (notify_page_fault(regs, esr))
return 0;
@@ -409,6 +412,25 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);
+ if (IS_ENABLED(CONFIG_SPECULATIVE_PAGE_FAULT)) {
+ fault = handle_speculative_fault(mm, addr, mm_flags, &vma);
+ /*
+ * Page fault is done if VM_FAULT_RETRY is not returned.
+ * But if the memory protection keys are active, we don't know
+ * if the fault is due to key mistmatch or due to a
+ * classic protection check.
+ * To differentiate that, we will need the VMA we no
+ * more have, so let's retry with the mmap_sem held.
+ */
+ if (fault != VM_FAULT_RETRY &&
+ fault != VM_FAULT_SIGSEGV) {
+ perf_sw_event(PERF_COUNT_SW_SPF, 1, regs, addr);
+ goto done;
+ }
+ } else {
+ vma = NULL;
+ }
+
/*
* As per x86, we may deadlock here. However, since the kernel only
* validly references user space from well defined areas of the code,
@@ -431,7 +453,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
#endif
}
- fault = __do_page_fault(mm, addr, mm_flags, vm_flags, tsk);
+ fault = __do_page_fault(mm, addr, mm_flags, vm_flags, tsk, vma);
major |= fault & VM_FAULT_MAJOR;
if (fault & VM_FAULT_RETRY) {
@@ -454,11 +476,21 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
if (mm_flags & FAULT_FLAG_ALLOW_RETRY) {
mm_flags &= ~FAULT_FLAG_ALLOW_RETRY;
mm_flags |= FAULT_FLAG_TRIED;
+
+ /*
+ * Do not try to reuse this vma and fetch it
+ * again since we will release the mmap_sem.
+ */
+ if (IS_ENABLED(CONFIG_SPECULATIVE_PAGE_FAULT))
+ vma = NULL;
+
goto retry;
}
}
up_read(&mm->mmap_sem);
+done:
+
/*
* Handle the "normal" (no error) case first.
*/
--
1.9.1
