[RFC 1/3] powerpc/mce: Bug fixes for MCE handling in kernel space

[Balbir Singh]

The code currently assumes PAGE_SHIFT as the shift value of
the pfn, this works correctly (mostly) for user space pages,
but the correct thing to do is

1. Extrace the shift value returned via the pte-walk API's
2. Use the shift value to access the instruction address.

Note, the final physical address still use PAGE_SHIFT for
computation. handle_ierror() is not modified and handle_derror()
is modified just for extracting the correct instruction
address.

Signed-off-by: Balbir Singh <bsingharora at gmail.com>
---
 arch/powerpc/kernel/mce_power.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/arch/powerpc/kernel/mce_power.c b/arch/powerpc/kernel/mce_power.c
index fe6fc63251fe..69c8cc1e8e4f 100644
--- a/arch/powerpc/kernel/mce_power.c
+++ b/arch/powerpc/kernel/mce_power.c
@@ -36,7 +36,8 @@
  * Convert an address related to an mm to a PFN. NOTE: we are in real
  * mode, we could potentially race with page table updates.
  */
-static unsigned long addr_to_pfn(struct pt_regs *regs, unsigned long addr)
+static unsigned long addr_to_pfn(struct pt_regs *regs, unsigned long addr,
+		unsigned int *shift)
 {
 	pte_t *ptep;
 	unsigned long flags;
@@ -49,9 +50,9 @@ static unsigned long addr_to_pfn(struct pt_regs *regs, unsigned long addr)
 
 	local_irq_save(flags);
 	if (mm == current->mm)
-		ptep = find_current_mm_pte(mm->pgd, addr, NULL, NULL);
+		ptep = find_current_mm_pte(mm->pgd, addr, NULL, shift);
 	else
-		ptep = find_init_mm_pte(addr, NULL);
+		ptep = find_init_mm_pte(addr, shift);
 	local_irq_restore(flags);
 	if (!ptep || pte_special(*ptep))
 		return ULONG_MAX;
@@ -353,13 +354,14 @@ static int mce_find_instr_ea_and_pfn(struct pt_regs *regs, uint64_t *addr,
 	unsigned long pfn, instr_addr;
 	struct instruction_op op;
 	struct pt_regs tmp = *regs;
+	unsigned int shift;
 
-	pfn = addr_to_pfn(regs, regs->nip);
+	pfn = addr_to_pfn(regs, regs->nip, &shift);
 	if (pfn != ULONG_MAX) {
-		instr_addr = (pfn << PAGE_SHIFT) + (regs->nip & ~PAGE_MASK);
+		instr_addr = (pfn << shift) + (regs->nip & ((1 << shift) - 1));
 		instr = *(unsigned int *)(instr_addr);
 		if (!analyse_instr(&op, &tmp, instr)) {
-			pfn = addr_to_pfn(regs, op.ea);
+			pfn = addr_to_pfn(regs, op.ea, &shift);
 			*addr = op.ea;
 			*phys_addr = (pfn << PAGE_SHIFT);
 			return 0;
@@ -437,7 +439,8 @@ static int mce_handle_ierror(struct pt_regs *regs,
 				unsigned long pfn;
 
 				if (get_paca()->in_mce < MAX_MCE_DEPTH) {
-					pfn = addr_to_pfn(regs, regs->nip);
+					pfn = addr_to_pfn(regs, regs->nip,
+							NULL);
 					if (pfn != ULONG_MAX) {
 						*phys_addr =
 							(pfn << PAGE_SHIFT);
-- 
2.13.6