mm: support poison recovery from do_cow_fault()

Patch series "mm: hwpoison: two more poison recovery".

One more CoW path to support poison recorvery in do_cow_fault(), and the
last copy_user_highpage() user is replaced to copy_mc_user_highpage() from
copy_present_page() during fork to support poison recorvery too.


This patch (of 2):

Like commit a873dfe ("mm, hwpoison: try to recover from copy-on
write faults"), there is another path which could crash because it does
not have recovery code where poison is consumed by the kernel in
do_cow_fault(), a crash calltrace shown below on old kernel, but it
could be happened in the lastest mainline code,

  CPU: 7 PID: 3248 Comm: mpi Kdump: loaded Tainted: G           OE     5.10.0 #1
  pc : copy_page+0xc/0xbc
  lr : copy_user_highpage+0x50/0x9c
  Call trace:
    copy_page+0xc/0xbc
    do_cow_fault+0x118/0x2bc
    do_fault+0x40/0x1a4
    handle_pte_fault+0x154/0x230
    __handle_mm_fault+0x1a8/0x38c
    handle_mm_fault+0xf0/0x250
    do_page_fault+0x184/0x454
    do_translation_fault+0xac/0xd4
    do_mem_abort+0x44/0xbc

Fix it by using copy_mc_user_highpage() to handle this case and return
VM_FAULT_HWPOISON for cow fault.

[[email protected]: unlock/put vmf->page, per Miaohe]
  Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Kefeng Wang <[email protected]>
Reviewed-by: Jane Chu <[email protected]>
Reviewed-by: Miaohe Lin <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Jiaqi Yan <[email protected]>
Cc: Naoya Horiguchi <[email protected]>
Cc: Tony Luck <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

mm/memory.c

@@ -5089,10 +5089,14 @@ static vm_fault_t do_cow_fault(struct vm_fault *vmf)
 	if (ret & VM_FAULT_DONE_COW)
 		return ret;
 
-	copy_user_highpage(vmf->cow_page, vmf->page, vmf->address, vma);
+	if (copy_mc_user_highpage(vmf->cow_page, vmf->page, vmf->address, vma)) {
+		ret = VM_FAULT_HWPOISON;
+		goto unlock;
+	}
 	__folio_mark_uptodate(folio);
 
 	ret |= finish_fault(vmf);
+unlock:
 	unlock_page(vmf->page);
 	put_page(vmf->page);
 	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))