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mm/memory: slightly simplify copy_present_pte()

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Let's move the pinning check into the caller, to simplify return code
logic and prepare for further changes: relocating the
page_needs_cow_for_dma() into rmap handling code.

While at it, remove the unused pte parameter and simplify the comments a
bit.

No functional change intended.

Link: https://lkml.kernel.org/r/20220428083441.37290-4-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
David Hildenbrand 2022-05-09 18:20:42 -07:00 committed by akpm
parent 623a1ddfeb
commit b51ad4f867
1 changed files with 16 additions and 37 deletions
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53
mm/memory.c
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@ -862,19 +862,11 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
}
/*
* Copy a present and normal page if necessary.
* Copy a present and normal page.
*
* NOTE! The usual case is that this doesn't need to do
* anything, and can just return a positive value. That
* will let the caller know that it can just increase
* the page refcount and re-use the pte the traditional
* way.
*
* But _if_ we need to copy it because it needs to be
* pinned in the parent (and the child should get its own
* copy rather than just a reference to the same page),
* we'll do that here and return zero to let the caller
* know we're done.
* NOTE! The usual case is that this isn't required;
* instead, the caller can just increase the page refcount
* and re-use the pte the traditional way.
*
* And if we need a pre-allocated page but don't yet have
* one, return a negative error to let the preallocation
@ -884,25 +876,10 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
static inline int
copy_present_page(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
pte_t *dst_pte, pte_t *src_pte, unsigned long addr, int *rss,
struct page **prealloc, pte_t pte, struct page *page)
struct page **prealloc, struct page *page)
{
struct page *new_page;
/*
* What we want to do is to check whether this page may
* have been pinned by the parent process. If so,
* instead of wrprotect the pte on both sides, we copy
* the page immediately so that we'll always guarantee
* the pinned page won't be randomly replaced in the
* future.
*
* The page pinning checks are just "has this mm ever
* seen pinning", along with the (inexact) check of
* the page count. That might give false positives for
* for pinning, but it will work correctly.
*/
if (likely(!page_needs_cow_for_dma(src_vma, page)))
return 1;
pte_t pte;
new_page = *prealloc;
if (!new_page)
@ -944,14 +921,16 @@ copy_present_pte(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
struct page *page;
page = vm_normal_page(src_vma, addr, pte);
if (page) {
int retval;
retval = copy_present_page(dst_vma, src_vma, dst_pte, src_pte,
addr, rss, prealloc, pte, page);
if (retval <= 0)
return retval;
if (page && unlikely(page_needs_cow_for_dma(src_vma, page))) {
/*
* If this page may have been pinned by the parent process,
* copy the page immediately for the child so that we'll always
* guarantee the pinned page won't be randomly replaced in the
* future.
*/
return copy_present_page(dst_vma, src_vma, dst_pte, src_pte,
addr, rss, prealloc, page);
} else if (page) {
get_page(page);
page_dup_rmap(page, false);
rss[mm_counter(page)]++;