The patch titled
Subject: mm/hugetlb: prepare hugetlb_follow_page_mask() for FOLL_PIN
has been added to the -mm mm-unstable branch. Its filename is
mm-hugetlb-prepare-hugetlb_follow_page_mask-for-foll_pin.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-hugetlb-prepare-hugetlb_follow_page_mask-for-foll_pin.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Peter Xu <peterx@xxxxxxxxxx>
Subject: mm/hugetlb: prepare hugetlb_follow_page_mask() for FOLL_PIN
Date: Wed, 28 Jun 2023 17:53:04 -0400
follow_page() doesn't use FOLL_PIN, meanwhile hugetlb seems to not be the
target of FOLL_WRITE either. However add the checks.
Namely, either the need to CoW due to missing write bit, or proper
unsharing on !AnonExclusive pages over R/O pins to reject the follow page.
That brings this function closer to follow_hugetlb_page().
So we don't care before, and also for now. But we'll care if we switch
over slow-gup to use hugetlb_follow_page_mask(). We'll also care when to
return -EMLINK properly, as that's the gup internal api to mean "we should
unshare". Not really needed for follow page path, though.
When at it, switching the try_grab_page() to use WARN_ON_ONCE(), to be
clear that it just should never fail. When error happens, instead of
setting page==NULL, capture the errno instead.
Link: https://lkml.kernel.org/r/20230628215310.73782-3-peterx@xxxxxxxxxx
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: James Houghton <jthoughton@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Kirill A . Shutemov <kirill@xxxxxxxxxxxxx>
Cc: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Mike Rapoport (IBM) <rppt@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/hugetlb.c | 33 ++++++++++++++++++++++-----------
1 file changed, 22 insertions(+), 11 deletions(-)
--- a/mm/hugetlb.c~mm-hugetlb-prepare-hugetlb_follow_page_mask-for-foll_pin
+++ a/mm/hugetlb.c
@@ -6462,13 +6462,7 @@ struct page *hugetlb_follow_page_mask(st
struct page *page = NULL;
spinlock_t *ptl;
pte_t *pte, entry;
-
- /*
- * FOLL_PIN is not supported for follow_page(). Ordinary GUP goes via
- * follow_hugetlb_page().
- */
- if (WARN_ON_ONCE(flags & FOLL_PIN))
- return NULL;
+ int ret;
hugetlb_vma_lock_read(vma);
pte = hugetlb_walk(vma, haddr, huge_page_size(h));
@@ -6478,8 +6472,23 @@ struct page *hugetlb_follow_page_mask(st
ptl = huge_pte_lock(h, mm, pte);
entry = huge_ptep_get(pte);
if (pte_present(entry)) {
- page = pte_page(entry) +
- ((address & ~huge_page_mask(h)) >> PAGE_SHIFT);
+ page = pte_page(entry);
+
+ if (!huge_pte_write(entry)) {
+ if (flags & FOLL_WRITE) {
+ page = NULL;
+ goto out;
+ }
+
+ if (gup_must_unshare(vma, flags, page)) {
+ /* Tell the caller to do unsharing */
+ page = ERR_PTR(-EMLINK);
+ goto out;
+ }
+ }
+
+ page += ((address & ~huge_page_mask(h)) >> PAGE_SHIFT);
+
/*
* Note that page may be a sub-page, and with vmemmap
* optimizations the page struct may be read only.
@@ -6489,8 +6498,10 @@ struct page *hugetlb_follow_page_mask(st
* try_grab_page() should always be able to get the page here,
* because we hold the ptl lock and have verified pte_present().
*/
- if (try_grab_page(page, flags)) {
- page = NULL;
+ ret = try_grab_page(page, flags);
+
+ if (WARN_ON_ONCE(ret)) {
+ page = ERR_PTR(ret);
goto out;
}
}
_
Patches currently in -mm which might be from peterx@xxxxxxxxxx are
mm-hugetlb-handle-foll_dump-well-in-follow_page_mask.patch
mm-hugetlb-prepare-hugetlb_follow_page_mask-for-foll_pin.patch
mm-hugetlb-add-page_mask-for-hugetlb_follow_page_mask.patch
mm-gup-cleanup-next_page-handling.patch
mm-gup-accelerate-thp-gup-even-for-pages-=-null.patch
mm-gup-retire-follow_hugetlb_page.patch
selftests-mm-add-a-to-run_vmtestssh.patch
selftests-mm-add-gup-test-matrix-in-run_vmtestssh.patch
