arm64: mm: Update perf accounting to handle poison faults

Re-organise the perf accounting for fault handling in preparation for
enabling handling of hardware poison faults in subsequent commits. The
change updates perf accounting to be inline with the behaviour on
x86.

With this update, the perf fault accounting -

  * Always report PERF_COUNT_SW_PAGE_FAULTS

  * Doesn't report anything else for VM_FAULT_ERROR (which includes
    hwpoison faults)

  * Reports PERF_COUNT_SW_PAGE_FAULTS_MAJ if it's a major
    fault (indicated by VM_FAULT_MAJOR)

  * Otherwise, reports PERF_COUNT_SW_PAGE_FAULTS_MIN

Change-Id: I4be2180ef9d046fb4f8edcbcc9dc30ce0c6622d2
Signed-off-by: Punit Agrawal <punit.agrawal@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index f840220..36d4bd5 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -339,7 +339,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
 {
 	struct task_struct *tsk;
 	struct mm_struct *mm;
-	int fault, sig, code;
+	int fault, sig, code, major = 0;
 	unsigned long vm_flags = VM_READ | VM_WRITE | VM_EXEC;
 	unsigned int mm_flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
 	struct vm_area_struct *vma = NULL;
@@ -380,6 +380,8 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
 			die("Accessing user space memory outside uaccess.h routines", regs, esr);
 	}
 
+	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);
+
 	/*
 	 * let's try a speculative page fault without grabbing the
 	 * mmap_sem.
@@ -414,6 +416,8 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
 		vma = find_vma(mm, addr);
 
 	fault = __do_page_fault(vma, addr, mm_flags, vm_flags, tsk);
+	major |= fault & VM_FAULT_MAJOR;
+
 	if (fault & VM_FAULT_RETRY) {
 		/*
 		 * If we need to retry but a fatal signal is pending, handle the
@@ -449,14 +453,17 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
 done:
 
 	/*
-	 * Major/minor page fault accounting is only done on the initial
-	 * attempt. If we go through a retry, it is extremely likely that the
-	 * page will be found in page cache at that point.
+	 * Handle the "normal" (no error) case first.
 	 */
-
-	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);
-	if (mm_flags & FAULT_FLAG_ALLOW_RETRY) {
-		if (fault & VM_FAULT_MAJOR) {
+	if (likely(!(fault & (VM_FAULT_ERROR | VM_FAULT_BADMAP |
+			      VM_FAULT_BADACCESS)))) {
+		/*
+		 * Major/minor page fault accounting is only done
+		 * once. If we go through a retry, it is extremely
+		 * likely that the page will be found in page cache at
+		 * that point.
+		 */
+		if (major) {
 			tsk->maj_flt++;
 			perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, regs,
 				      addr);
@@ -465,14 +472,8 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
 			perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, regs,
 				      addr);
 		}
-	}
-
-	/*
-	 * Handle the "normal" case first - VM_FAULT_MAJOR
-	 */
-	if (likely(!(fault & (VM_FAULT_ERROR | VM_FAULT_BADMAP |
-			      VM_FAULT_BADACCESS))))
 		return 0;
+	}
 
 	/*
 	 * If we are in kernel mode at this point, we have no context to