[PATCH v3 20/27] hugetlb/userfaultfd: Handle UFFDIO_WRITEPROTECT

Peter Xu
2021-05-27T20:23:31Z

This starts from passing cp_flags into hugetlb_change_protection() so hugetlb
will be able to handle MM_CP_UFFD_WP[_RESOLVE] requests.

huge_pte_clear_uffd_wp() is introduced to handle the case where the
UFFDIO_WRITEPROTECT is requested upon migrating huge page entries.

Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
include/linux/hugetlb.h | 6 ++++--
mm/hugetlb.c | 13 ++++++++++++-
mm/mprotect.c | 3 ++-
mm/userfaultfd.c | 8 ++++++++
4 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index d238a69bcbb3..3e4c5c64d867 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -204,7 +204,8 @@ struct page *follow_huge_pgd(struct mm_struct *mm, unsigned long address,
int pmd_huge(pmd_t pmd);
int pud_huge(pud_t pud);
unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
- unsigned long address, unsigned long end, pgprot_t newprot);
+ unsigned long address, unsigned long end, pgprot_t newprot,
+ unsigned long cp_flags);

bool is_hugetlb_entry_migration(pte_t pte);
void hugetlb_unshare_all_pmds(struct vm_area_struct *vma);
@@ -368,7 +369,8 @@ static inline void move_hugetlb_state(struct page *oldpage,

static inline unsigned long hugetlb_change_protection(
struct vm_area_struct *vma, unsigned long address,
- unsigned long end, pgprot_t newprot)
+ unsigned long end, pgprot_t newprot,
+ unsigned long cp_flags)
{
return 0;
}
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 9bdcc208f5d9..b101c3af3ab5 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5444,7 +5444,8 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
}

unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
- unsigned long address, unsigned long end, pgprot_t newprot)
+ unsigned long address, unsigned long end,
+ pgprot_t newprot, unsigned long cp_flags)
{
struct mm_struct *mm = vma->vm_mm;
unsigned long start = address;
@@ -5454,6 +5455,8 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
unsigned long pages = 0;
bool shared_pmd = false;
struct mmu_notifier_range range;
+ bool uffd_wp = cp_flags & MM_CP_UFFD_WP;
+ bool uffd_wp_resolve = cp_flags & MM_CP_UFFD_WP_RESOLVE;

/*
* In the case of shared PMDs, the area to flush could be beyond
@@ -5495,6 +5498,10 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
entry = make_readable_migration_entry(
swp_offset(entry));
newpte = swp_entry_to_pte(entry);
+ if (uffd_wp)
+ newpte = pte_swp_mkuffd_wp(newpte);
+ else if (uffd_wp_resolve)
+ newpte = pte_swp_clear_uffd_wp(newpte);
set_huge_swap_pte_at(mm, address, ptep,
newpte, huge_page_size(h));
pages++;
@@ -5509,6 +5516,10 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
old_pte = huge_ptep_modify_prot_start(vma, address, ptep);
pte = pte_mkhuge(huge_pte_modify(old_pte, newprot));
pte = arch_make_huge_pte(pte, shift, vma->vm_flags);
+ if (uffd_wp)
+ pte = huge_pte_mkuffd_wp(huge_pte_wrprotect(pte));
+ else if (uffd_wp_resolve)
+ pte = huge_pte_clear_uffd_wp(pte);
huge_ptep_modify_prot_commit(vma, address, ptep, old_pte, pte);
pages++;
}
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 3fcb87b59696..96f4df023439 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -426,7 +426,8 @@ unsigned long change_protection(struct vm_area_struct *vma, unsigned long start,
BUG_ON((cp_flags & MM_CP_UFFD_WP_ALL) == MM_CP_UFFD_WP_ALL);

if (is_vm_hugetlb_page(vma))
- pages = hugetlb_change_protection(vma, start, end, newprot);
+ pages = hugetlb_change_protection(vma, start, end, newprot,
+ cp_flags);
else
pages = change_protection_range(vma, start, end, newprot,
cp_flags);
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 424d0adc3f80..82c235f555b8 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -743,6 +743,7 @@ int mwriteprotect_range(struct mm_struct *dst_mm, unsigned long start,
unsigned long len, bool enable_wp, bool *mmap_changing)
{
struct vm_area_struct *dst_vma;
+ unsigned long page_mask;
pgprot_t newprot;
int err;

@@ -779,6 +780,13 @@ int mwriteprotect_range(struct mm_struct *dst_mm, unsigned long start,
if (!vma_is_anonymous(dst_vma))
goto out_unlock;

+ if (is_vm_hugetlb_page(dst_vma)) {
+ err = -EINVAL;
+ page_mask = vma_kernel_pagesize(dst_vma) - 1;
+ if ((start & page_mask) || (len & page_mask))
+ goto out_unlock;
+ }
+
if (enable_wp)
newprot = vm_get_page_prot(dst_vma->vm_flags & ~(VM_WRITE));
else
--
2.31.1