powerpc/mm/mce: Keep irqs disabled during lockless page table walk

__find_linux_mm_pte() returns a page table entry pointer after walking
the page table without holding locks. To make it safe against a THP
split and/or collapse, we disable interrupts around the lockless page
table walk. However we need to keep interrupts disabled as long as we
use the page table entry pointer that is returned.

Fix addr_to_pfn() to do that.

Fixes: ba41e1e1ccb9 ("powerpc/mce: Hookup derror (load/store) UE errors")
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
[mpe: Rearrange code slightly and tweak change log wording]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190918145328.28602-1-aneesh.kumar@linux.ibm.com

diff --git a/arch/powerpc/kernel/mce_power.c b/arch/powerpc/kernel/mce_power.c
index 356e7b99f66188dec49d104fd58f8c4d143b1740..1cbf7f1a4e3d899c6008d12f9d6f683adb3906bf 100644 (file)
--- a/arch/powerpc/kernel/mce_power.c
+++ b/arch/powerpc/kernel/mce_power.c
@@ -29,7 +29,7 @@ unsigned long addr_to_pfn(struct pt_regs *regs, unsigned long addr)
 {
        pte_t *ptep;
        unsigned int shift;
-       unsigned long flags;
+       unsigned long pfn, flags;
        struct mm_struct *mm;
 
        if (user_mode(regs))
@@ -39,18 +39,22 @@ unsigned long addr_to_pfn(struct pt_regs *regs, unsigned long addr)
 
        local_irq_save(flags);
        ptep = __find_linux_pte(mm->pgd, addr, NULL, &shift);
-       local_irq_restore(flags);
 
-       if (!ptep || pte_special(*ptep))
-               return ULONG_MAX;
+       if (!ptep || pte_special(*ptep)) {
+               pfn = ULONG_MAX;
+               goto out;
+       }
 
-       if (shift > PAGE_SHIFT) {
+       if (shift <= PAGE_SHIFT)
+               pfn = pte_pfn(*ptep);
+       else {
                unsigned long rpnmask = (1ul << shift) - PAGE_SIZE;
-
-               return pte_pfn(__pte(pte_val(*ptep) | (addr & rpnmask)));
+               pfn = pte_pfn(__pte(pte_val(*ptep) | (addr & rpnmask)));
        }
 
-       return pte_pfn(*ptep);
+out:
+       local_irq_restore(flags);
+       return pfn;
 }
 
 /* flush SLBs and reload */