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mm/hugetlb: prepare hugetlb_follow_page_mask() for FOLL_PIN

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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@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: James Houghton <jthoughton@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Kirill A . Shutemov <kirill@shutemov.name>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Peter Xu 2023-06-28 17:53:04 -04:00 committed by Andrew Morton
parent dd767aaa2f
commit 458568c929
1 changed files with 22 additions and 11 deletions
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33
mm/hugetlb.c
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@ -6462,13 +6462,7 @@ struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma,
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(struct vm_area_struct *vma,
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(struct vm_area_struct *vma,
* 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;
}
}