Re: [PATCH v3 2/2] s390/mm: re-enable the shared zeropage for !PV and !skeys KVM guests

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On 16.04.24 08:37, Alexander Gordeev wrote:
On Mon, Apr 15, 2024 at 09:14:03PM +0200, David Hildenbrand wrote:
+retry:
+		rc = walk_page_range_vma(vma, addr, vma->vm_end,
+					 &find_zeropage_ops, &addr);
+		if (rc <= 0)
+			continue;

So in case an error is returned for the last vma, __s390_unshare_zeropage()
finishes with that error. By contrast, the error for a non-last vma would
be ignored?

Right, it looks a bit off. walk_page_range_vma() shouldn't fail
unless find_zeropage_pte_entry() would fail -- which would also be
very unexpected.

To handle it cleanly in case we would ever get a weird zeropage where we
don't expect it, we should probably just exit early.

Something like the following (not compiled, addressing the comment below):

@@ -2618,7 +2618,8 @@ static int __s390_unshare_zeropages(struct mm_struct *mm)
  	struct vm_area_struct *vma;
  	VMA_ITERATOR(vmi, mm, 0);
  	unsigned long addr;
-	int rc;
+	vm_fault_t rc;
+	int zero_page;

I would use "fault" for mm faults (just like everywhere else handle_mm_fault() is
called) and leave rc as is:

	vm_fault_t fault;
	int rc;

Sure, let me know once discussion here stopped whether you want a v4 or can fix that up.

--
Cheers,

David / dhildenb





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