[PATCH v2 1/6] riscv/mm/fault: simplify code for do_page_fault()

Palmer Dabbelt
2023-03-15T03:05:30Z

From: Tong Tiangen <tongtiangen@huawei.com>

To make the code more hierarchical and readable, we fold vma related
judgments into __do_page_fault(). And to simplify the code, move the
tsk->thread.bad_cause's setting into bad_area(). No functional change
intended.

Signed-off-by: Tong Tiangen <tongtiangen@huawei.com>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
---
arch/riscv/mm/fault.c | 77 +++++++++++++++++++++++--------------------
1 file changed, 41 insertions(+), 36 deletions(-)

diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
index 460f785f6e09..0a8c9afeee22 100644
--- a/arch/riscv/mm/fault.c
+++ b/arch/riscv/mm/fault.c
@@ -85,6 +85,8 @@ static inline void mm_fault_error(struct pt_regs *regs, unsigned long addr, vm_f

static inline void bad_area(struct pt_regs *regs, struct mm_struct *mm, int code, unsigned long addr)
{
+ current->thread.bad_cause = regs->cause;
+
/*
* Something tried to access memory that isn't in our memory map.
* Fix it, but check if it's kernel or user first.
@@ -200,6 +202,38 @@ static inline bool access_error(unsigned long cause, struct vm_area_struct *vma)
return false;
}

+#define VM_FAULT_BADMAP ((__force vm_fault_t)0x010000)
+#define VM_FAULT_BADACCESS ((__force vm_fault_t)0x020000)
+
+static vm_fault_t __do_page_fault(struct mm_struct *mm, unsigned long addr,
+ unsigned int mm_flags, struct pt_regs *regs)
+{
+ struct vm_area_struct *vma = find_vma(mm, addr);
+
+ if (unlikely(!vma))
+ return VM_FAULT_BADMAP;
+
+ if (unlikely(vma->vm_start > addr)) {
+ if (unlikely(!(vma->vm_flags & VM_GROWSDOWN) ||
+ expand_stack(vma, addr)))
+ return VM_FAULT_BADMAP;
+ }
+
+ /*
+ * Ok, we have a good vm_area for this memory access, so
+ * we can handle it.
+ */
+ if (unlikely(access_error(regs->cause, vma)))
+ return VM_FAULT_BADACCESS;
+
+ /*
+ * If for any reason at all we could not handle the fault,
+ * make sure we exit gracefully rather than endlessly redo
+ * the fault.
+ */
+ return handle_mm_fault(vma, addr, mm_flags, regs);
+}
+
/*
* This routine handles page faults. It determines the address and the
* problem, and then passes it off to one of the appropriate routines.
@@ -207,7 +241,6 @@ static inline bool access_error(unsigned long cause, struct vm_area_struct *vma)
asmlinkage void do_page_fault(struct pt_regs *regs)
{
struct task_struct *tsk;
- struct vm_area_struct *vma;
struct mm_struct *mm;
unsigned long addr, cause;
unsigned int flags = FAULT_FLAG_DEFAULT;
@@ -282,44 +315,16 @@ asmlinkage void do_page_fault(struct pt_regs *regs)
flags |= FAULT_FLAG_INSTRUCTION;
retry:
mmap_read_lock(mm);
- vma = find_vma(mm, addr);
- if (unlikely(!vma)) {
- tsk->thread.bad_cause = cause;
- bad_area(regs, mm, code, addr);
- return;
- }
- if (likely(vma->vm_start <= addr))
- goto good_area;
- if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) {
- tsk->thread.bad_cause = cause;
- bad_area(regs, mm, code, addr);
- return;
- }
- if (unlikely(expand_stack(vma, addr))) {
- tsk->thread.bad_cause = cause;
- bad_area(regs, mm, code, addr);
- return;
- }

- /*
- * Ok, we have a good vm_area for this memory access, so
- * we can handle it.
- */
-good_area:
- code = SEGV_ACCERR;
+ fault = __do_page_fault(mm, addr, flags, regs);

- if (unlikely(access_error(cause, vma))) {
- tsk->thread.bad_cause = cause;
- bad_area(regs, mm, code, addr);
- return;
- }
+ if (unlikely(fault & VM_FAULT_BADMAP))
+ return bad_area(regs, mm, code, addr);

- /*
- * If for any reason at all we could not handle the fault,
- * make sure we exit gracefully rather than endlessly redo
- * the fault.
- */
- fault = handle_mm_fault(vma, addr, flags, regs);
+ if (unlikely(fault & VM_FAULT_BADACCESS)) {
+ code = SEGV_ACCERR;
+ return bad_area(regs, mm, code, addr);
+ }

/*
* If we need to retry but a fatal signal is pending, handle the
--
2.39.2