On 10/30/22 11:52, Nadav Amit wrote:
On Oct 30, 2022, at 11:43 AM, Peter Xu peterx@redhat.com wrote:
The loop comes from 7e027b14d53e ("vm: simplify unmap_vmas() calling convention", 2012-05-06), where zap_page_range() was used to replace a call to unmap_vmas() because the patch wanted to eliminate the zap details pointer for unmap_vmas(), which makes sense.
I didn't check the old code, but from what I can tell (and also as Mike pointed out) I don't think zap_page_range() in the lastest code base is ever used on multi-vma at all. Otherwise the mmu notifier is already broken - see mmu_notifier_range_init() where the vma pointer is also part of the notification.
Perhaps we should just remove the loop?
There is already zap_page_range_single() that does exactly that. Just need to export it.
I was thinking that zap_page_range() should perform a notification call for each vma within the loop. Something like this?
@@ -1704,15 +1704,21 @@ void zap_page_range(struct vm_area_struct *vma, unsigned long start, MA_STATE(mas, mt, vma->vm_end, vma->vm_end);
lru_add_drain(); - mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm, - start, start + size); tlb_gather_mmu(&tlb, vma->vm_mm); update_hiwater_rss(vma->vm_mm); - mmu_notifier_invalidate_range_start(&range); do { - unmap_single_vma(&tlb, vma, start, range.end, NULL); + mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, + vma->vm_mm, + max(start, vma->vm_start), + min(start + size, vma->vm_end)); + if (is_vm_hugetlb_page(vma)) + adjust_range_if_pmd_sharing_possible(vma, + &range.start, + &range.end); + mmu_notifier_invalidate_range_start(&range); + unmap_single_vma(&tlb, vma, start, start + size, NULL); + mmu_notifier_invalidate_range_end(&range); } while ((vma = mas_find(&mas, end - 1)) != NULL); - mmu_notifier_invalidate_range_end(&range); tlb_finish_mmu(&tlb); }
One thing to keep in mind is that this patch is a fix that must be backported to stable. Therefore, I do not think we want to add too many changes out of the direct scope of the fix.
We can always change things like this in follow up patches.