On 11.06.24 16:46, David Hildenbrand wrote:
On 11.06.24 16:18, Andrew Bresticker wrote:
The requirement that the head page be passed to do_set_pmd() was added
in commit ef37b2ea08ac ("mm/memory: page_add_file_rmap() ->
folio_add_file_rmap_[pte|pmd]()") and prevents pmd-mapping in the
finish_fault() path if vmf->page is anything but the head page for an
otherwise suitable vma and pmd-sized page. Have finish_fault() pass in
the head page instead.
Fixes: ef37b2ea08ac ("mm/memory: page_add_file_rmap() -> folio_add_file_rmap_[pte|pmd]()")
Signed-off-by: Andrew Bresticker <abrestic@xxxxxxxxxxxx>
---
mm/memory.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/memory.c b/mm/memory.c
index 0f47a533014e..f13b953b507c 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4764,7 +4764,7 @@ vm_fault_t finish_fault(struct vm_fault *vmf)
if (pmd_none(*vmf->pmd)) {
if (PageTransCompound(page)) {
- ret = do_set_pmd(vmf, page);
+ ret = do_set_pmd(vmf, compound_head(page));
if (ret != VM_FAULT_FALLBACK)
return ret;
}
That certainly makes the "page != &folio->page" check happy.
It is *likely* incorrect if we would ever have folios > PMD size (which
we don't have on that path yet).
I assume that the thp_vma_suitable_order() check would detect any kind
of "different placement of the folio in virtual address space", where we
could mess up.
Question is: should we instead drop the "page != &folio->page" check
that I added?
To be precise, the something like following:
diff --git a/mm/memory.c b/mm/memory.c
index 5e633c9c27a8b..76f48dc5899cd 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4699,8 +4699,9 @@ vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page)
if (!thp_vma_suitable_order(vma, haddr, PMD_ORDER))
return ret;
- if (page != &folio->page || folio_order(folio) != HPAGE_PMD_ORDER)
+ if (folio_order(folio) != HPAGE_PMD_ORDER)
return ret;
+ page = &folio->page;
/*
* Just backoff if any subpage of a THP is corrupted otherwise
--
Cheers,
David / dhildenb
