[PATCH v2 4/7] powerpc: mm: accelerate pagefault when badaccess

[Kefeng Wang]

The access_[pkey]_error() of vma already checked under per-VMA lock, if
it is a bad access, directly handle error, no need to retry with mmap_lock
again. In order to release the correct lock, pass the mm_struct into
bad_access_pkey()/bad_access(), if mm is NULL, release vma lock, or
release mmap_lock. Since the page faut is handled under per-VMA lock,
count it as a vma lock event with VMA_LOCK_SUCCESS.

Signed-off-by: Kefeng Wang <wangkefeng.wang at huawei.com>
---
 arch/powerpc/mm/fault.c | 33 ++++++++++++++++++++-------------
 1 file changed, 20 insertions(+), 13 deletions(-)

diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 53335ae21a40..215690452495 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -71,23 +71,26 @@ static noinline int bad_area_nosemaphore(struct pt_regs *regs, unsigned long add
 	return __bad_area_nosemaphore(regs, address, SEGV_MAPERR);
 }
 
-static int __bad_area(struct pt_regs *regs, unsigned long address, int si_code)
+static int __bad_area(struct pt_regs *regs, unsigned long address, int si_code,
+		      struct mm_struct *mm, struct vm_area_struct *vma)
 {
-	struct mm_struct *mm = current->mm;
 
 	/*
 	 * Something tried to access memory that isn't in our memory map..
 	 * Fix it, but check if it's kernel or user first..
 	 */
-	mmap_read_unlock(mm);
+	if (mm)
+		mmap_read_unlock(mm);
+	else
+		vma_end_read(vma);
 
 	return __bad_area_nosemaphore(regs, address, si_code);
 }
 
 static noinline int bad_access_pkey(struct pt_regs *regs, unsigned long address,
+				    struct mm_struct *mm,
 				    struct vm_area_struct *vma)
 {
-	struct mm_struct *mm = current->mm;
 	int pkey;
 
 	/*
@@ -109,7 +112,10 @@ static noinline int bad_access_pkey(struct pt_regs *regs, unsigned long address,
 	 */
 	pkey = vma_pkey(vma);
 
-	mmap_read_unlock(mm);
+	if (mm)
+		mmap_read_unlock(mm);
+	else
+		vma_end_read(vma);
 
 	/*
 	 * If we are in kernel mode, bail out with a SEGV, this will
@@ -124,9 +130,10 @@ static noinline int bad_access_pkey(struct pt_regs *regs, unsigned long address,
 	return 0;
 }
 
-static noinline int bad_access(struct pt_regs *regs, unsigned long address)
+static noinline int bad_access(struct pt_regs *regs, unsigned long address,
+			       struct mm_struct *mm, struct vm_area_struct *vma)
 {
-	return __bad_area(regs, address, SEGV_ACCERR);
+	return __bad_area(regs, address, SEGV_ACCERR, mm, vma);
 }
 
 static int do_sigbus(struct pt_regs *regs, unsigned long address,
@@ -479,13 +486,13 @@ static int ___do_page_fault(struct pt_regs *regs, unsigned long address,
 
 	if (unlikely(access_pkey_error(is_write, is_exec,
 				       (error_code & DSISR_KEYFAULT), vma))) {
-		vma_end_read(vma);
-		goto lock_mmap;
+		count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
+		return bad_access_pkey(regs, address, NULL, vma);
 	}
 
 	if (unlikely(access_error(is_write, is_exec, vma))) {
-		vma_end_read(vma);
-		goto lock_mmap;
+		count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
+		return bad_access(regs, address, NULL, vma);
 	}
 
 	fault = handle_mm_fault(vma, address, flags | FAULT_FLAG_VMA_LOCK, regs);
@@ -521,10 +528,10 @@ static int ___do_page_fault(struct pt_regs *regs, unsigned long address,
 
 	if (unlikely(access_pkey_error(is_write, is_exec,
 				       (error_code & DSISR_KEYFAULT), vma)))
-		return bad_access_pkey(regs, address, vma);
+		return bad_access_pkey(regs, address, mm, vma);
 
 	if (unlikely(access_error(is_write, is_exec, vma)))
-		return bad_access(regs, address);
+		return bad_access(regs, address, mm, vma);
 
 	/*
 	 * If for any reason at all we couldn't handle the fault,
-- 
2.27.0