[PATCH v2 9/9] userfaultfd/shmem: modify shmem_mcopy_atomic_pte to use install_ptes
From: Axel Rasmussen
Date: Tue Apr 13 2021 - 01:18:07 EST
In a previous commit, we added the mcopy_atomic_install_ptes() helper.
This helper does the job of setting up PTEs for an existing page, to map
it into a given VMA. It deals with both the anon and shmem cases, as
well as the shared and private cases.
In other words, shmem_mcopy_atomic_pte() duplicates a case it already
handles. So, expose it, and let shmem_mcopy_atomic_pte() use it
directly, to reduce code duplication.
This requires that we refactor shmem_mcopy_atomic-pte() a bit:
Instead of doing accounting (shmem_recalc_inode() et al) part-way
through the PTE setup, do it beforehand. This frees up
mcopy_atomic_install_ptes() from having to care about this accounting,
but it does mean we need to clean it up if we get a failure afterwards
(shmem_uncharge()).
We can *almost* use shmem_charge() to do this, reducing code
duplication. But, it does `inode->i_mapping->nrpages++`, which would
double-count since shmem_add_to_page_cache() also does this.
Signed-off-by: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
---
include/linux/userfaultfd_k.h | 5 ++++
mm/shmem.c | 52 +++++++----------------------------
mm/userfaultfd.c | 25 ++++++++---------
3 files changed, 27 insertions(+), 55 deletions(-)
diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h
index 794d1538b8ba..3e20bfa9ef80 100644
--- a/include/linux/userfaultfd_k.h
+++ b/include/linux/userfaultfd_k.h
@@ -53,6 +53,11 @@ enum mcopy_atomic_mode {
MCOPY_ATOMIC_CONTINUE,
};
+extern int mcopy_atomic_install_ptes(struct mm_struct *dst_mm, pmd_t *dst_pmd,
+ struct vm_area_struct *dst_vma,
+ unsigned long dst_addr, struct page *page,
+ bool newly_allocated, bool wp_copy);
+
extern ssize_t mcopy_atomic(struct mm_struct *dst_mm, unsigned long dst_start,
unsigned long src_start, unsigned long len,
bool *mmap_changing, __u64 mode);
diff --git a/mm/shmem.c b/mm/shmem.c
index 3f48cb5e8404..9b12298405a4 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2376,10 +2376,8 @@ int shmem_mcopy_atomic_pte(struct mm_struct *dst_mm,
struct address_space *mapping = inode->i_mapping;
gfp_t gfp = mapping_gfp_mask(mapping);
pgoff_t pgoff = linear_page_index(dst_vma, dst_addr);
- spinlock_t *ptl;
void *page_kaddr;
struct page *page;
- pte_t _dst_pte, *dst_pte;
int ret;
pgoff_t max_off;
@@ -2389,8 +2387,10 @@ int shmem_mcopy_atomic_pte(struct mm_struct *dst_mm,
if (!*pagep) {
page = shmem_alloc_page(gfp, info, pgoff);
- if (!page)
- goto out_unacct_blocks;
+ if (!page) {
+ shmem_inode_unacct_blocks(inode, 1);
+ goto out;
+ }
if (!zeropage) { /* COPY */
page_kaddr = kmap_atomic(page);
@@ -2430,59 +2430,27 @@ int shmem_mcopy_atomic_pte(struct mm_struct *dst_mm,
if (ret)
goto out_release;
- _dst_pte = mk_pte(page, dst_vma->vm_page_prot);
- if (dst_vma->vm_flags & VM_WRITE)
- _dst_pte = pte_mkwrite(pte_mkdirty(_dst_pte));
- else {
- /*
- * We don't set the pte dirty if the vma has no
- * VM_WRITE permission, so mark the page dirty or it
- * could be freed from under us. We could do it
- * unconditionally before unlock_page(), but doing it
- * only if VM_WRITE is not set is faster.
- */
- set_page_dirty(page);
- }
-
- dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
-
- ret = -EFAULT;
- max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
- if (unlikely(pgoff >= max_off))
- goto out_release_unlock;
-
- ret = -EEXIST;
- if (!pte_none(*dst_pte))
- goto out_release_unlock;
-
- lru_cache_add(page);
-
spin_lock_irq(&info->lock);
info->alloced++;
inode->i_blocks += BLOCKS_PER_PAGE;
shmem_recalc_inode(inode);
spin_unlock_irq(&info->lock);
- inc_mm_counter(dst_mm, mm_counter_file(page));
- page_add_file_rmap(page, false);
- set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
+ ret = mcopy_atomic_install_ptes(dst_mm, dst_pmd, dst_vma, dst_addr,
+ page, true, false);
+ if (ret)
+ goto out_release_uncharge;
- /* No need to invalidate - it was non-present before */
- update_mmu_cache(dst_vma, dst_addr, dst_pte);
- pte_unmap_unlock(dst_pte, ptl);
unlock_page(page);
ret = 0;
out:
return ret;
-out_release_unlock:
- pte_unmap_unlock(dst_pte, ptl);
- ClearPageDirty(page);
+out_release_uncharge:
delete_from_page_cache(page);
+ shmem_uncharge(inode, 1);
out_release:
unlock_page(page);
put_page(page);
-out_unacct_blocks:
- shmem_inode_unacct_blocks(inode, 1);
goto out;
}
#endif /* CONFIG_USERFAULTFD */
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 8df0438f5d6a..3f73ba0b99f0 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -51,18 +51,13 @@ struct vm_area_struct *find_dst_vma(struct mm_struct *dst_mm,
/*
* Install PTEs, to map dst_addr (within dst_vma) to page.
*
- * This function handles MCOPY_ATOMIC_CONTINUE (which is always file-backed),
- * whether or not dst_vma is VM_SHARED. It also handles the more general
- * MCOPY_ATOMIC_NORMAL case, when dst_vma is *not* VM_SHARED (it may be file
- * backed, or not).
- *
- * Note that MCOPY_ATOMIC_NORMAL for a VM_SHARED dst_vma is handled by
- * shmem_mcopy_atomic_pte instead.
+ * This function handles both MCOPY_ATOMIC_NORMAL and _CONTINUE for both shmem
+ * and anon, and for both shared and private VMAs.
*/
-static int mcopy_atomic_install_ptes(struct mm_struct *dst_mm, pmd_t *dst_pmd,
- struct vm_area_struct *dst_vma,
- unsigned long dst_addr, struct page *page,
- bool newly_allocated, bool wp_copy)
+int mcopy_atomic_install_ptes(struct mm_struct *dst_mm, pmd_t *dst_pmd,
+ struct vm_area_struct *dst_vma,
+ unsigned long dst_addr, struct page *page,
+ bool newly_allocated, bool wp_copy)
{
int ret;
pte_t _dst_pte, *dst_pte;
@@ -116,8 +111,12 @@ static int mcopy_atomic_install_ptes(struct mm_struct *dst_mm, pmd_t *dst_pmd,
else
page_add_new_anon_rmap(page, dst_vma, dst_addr, false);
- if (newly_allocated)
- lru_cache_add_inactive_or_unevictable(page, dst_vma);
+ if (newly_allocated) {
+ if (vma_is_shmem(dst_vma) && vm_shared)
+ lru_cache_add(page);
+ else
+ lru_cache_add_inactive_or_unevictable(page, dst_vma);
+ }
set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
--
2.31.1.295.g9ea45b61b8-goog