userfaultfd: hugetlbfs: add __mcopy_atomic_hugetlb for huge page UFFDIO_COPY

__mcopy_atomic_hugetlb performs the UFFDIO_COPY operation for huge
pages.  It is based on the existing __mcopy_atomic routine for normal
pages.  Unlike normal pages, there is no huge page support for the
UFFDIO_ZEROPAGE operation.

Link: http://lkml.kernel.org/r/20161216144821.5183-19-aarcange@redhat.com
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Michael Rapoport <RAPOPORT@il.ibm.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 186 insertions, 0 deletions

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 9c2ed70ac78d..ef0495bfd17a 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -14,6 +14,8 @@
 #include <linux/swapops.h>
 #include <linux/userfaultfd_k.h>
 #include <linux/mmu_notifier.h>
+#include <linux/hugetlb.h>
+#include <linux/pagemap.h>
 #include <asm/tlbflush.h>
 #include "internal.h"
 
@@ -139,6 +141,183 @@ static pmd_t *mm_alloc_pmd(struct mm_struct *mm, unsigned long address)
         return pmd;
 }
 
+#ifdef CONFIG_HUGETLB_PAGE
+/*
+ * __mcopy_atomic processing for HUGETLB vmas.  Note that this routine is
+ * called with mmap_sem held, it will release mmap_sem before returning.
+ */
+static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm,
+                                              struct vm_area_struct *dst_vma,
+                                              unsigned long dst_start,
+                                              unsigned long src_start,
+                                              unsigned long len,
+                                              bool zeropage)
+{
+        ssize_t err;
+        pte_t *dst_pte;
+        unsigned long src_addr, dst_addr;
+        long copied;
+        struct page *page;
+        struct hstate *h;
+        unsigned long vma_hpagesize;
+        pgoff_t idx;
+        u32 hash;
+        struct address_space *mapping;
+
+        /*
+         * There is no default zero huge page for all huge page sizes as
+         * supported by hugetlb.  A PMD_SIZE huge pages may exist as used
+         * by THP.  Since we can not reliably insert a zero page, this
+         * feature is not supported.
+         */
+        if (zeropage) {
+                up_read(&dst_mm->mmap_sem);
+                return -EINVAL;
+        }
+
+        src_addr = src_start;
+        dst_addr = dst_start;
+        copied = 0;
+        page = NULL;
+        vma_hpagesize = vma_kernel_pagesize(dst_vma);
+
+        /*
+         * Validate alignment based on huge page size
+         */
+        err = -EINVAL;
+        if (dst_start & (vma_hpagesize - 1) || len & (vma_hpagesize - 1))
+                goto out_unlock;
+
+retry:
+        /*
+         * On routine entry dst_vma is set.  If we had to drop mmap_sem and
+         * retry, dst_vma will be set to NULL and we must lookup again.
+         */
+        if (!dst_vma) {
+                err = -EINVAL;
+                dst_vma = find_vma(dst_mm, dst_start);
+                if (!dst_vma || !is_vm_hugetlb_page(dst_vma))
+                        goto out_unlock;
+
+                if (vma_hpagesize != vma_kernel_pagesize(dst_vma))
+                        goto out_unlock;
+
+                /*
+                 * Make sure the vma is not shared, that the remaining dst
+                 * range is both valid and fully within a single existing vma.
+                 */
+                if (dst_vma->vm_flags & VM_SHARED)
+                        goto out_unlock;
+                if (dst_start < dst_vma->vm_start ||
+                    dst_start + len > dst_vma->vm_end)
+                        goto out_unlock;
+        }
+
+        if (WARN_ON(dst_addr & (vma_hpagesize - 1) ||
+                    (len - copied) & (vma_hpagesize - 1)))
+                goto out_unlock;
+
+        /*
+         * Only allow __mcopy_atomic_hugetlb on userfaultfd registered ranges.
+         */
+        if (!dst_vma->vm_userfaultfd_ctx.ctx)
+                goto out_unlock;
+
+        /*
+         * Ensure the dst_vma has a anon_vma.
+         */
+        err = -ENOMEM;
+        if (unlikely(anon_vma_prepare(dst_vma)))
+                goto out_unlock;
+
+        h = hstate_vma(dst_vma);
+
+        while (src_addr < src_start + len) {
+                pte_t dst_pteval;
+
+                BUG_ON(dst_addr >= dst_start + len);
+                VM_BUG_ON(dst_addr & ~huge_page_mask(h));
+
+                /*
+                 * Serialize via hugetlb_fault_mutex
+                 */
+                idx = linear_page_index(dst_vma, dst_addr);
+                mapping = dst_vma->vm_file->f_mapping;
+                hash = hugetlb_fault_mutex_hash(h, dst_mm, dst_vma, mapping,
+                                                                idx, dst_addr);
+                mutex_lock(&hugetlb_fault_mutex_table[hash]);
+
+                err = -ENOMEM;
+                dst_pte = huge_pte_alloc(dst_mm, dst_addr, huge_page_size(h));
+                if (!dst_pte) {
+                        mutex_unlock(&hugetlb_fault_mutex_table[hash]);
+                        goto out_unlock;
+                }
+
+                err = -EEXIST;
+                dst_pteval = huge_ptep_get(dst_pte);
+                if (!huge_pte_none(dst_pteval)) {
+                        mutex_unlock(&hugetlb_fault_mutex_table[hash]);
+                        goto out_unlock;
+                }
+
+                err = hugetlb_mcopy_atomic_pte(dst_mm, dst_pte, dst_vma,
+                                                dst_addr, src_addr, &page);
+
+                mutex_unlock(&hugetlb_fault_mutex_table[hash]);
+
+                cond_resched();
+
+                if (unlikely(err == -EFAULT)) {
+                        up_read(&dst_mm->mmap_sem);
+                        BUG_ON(!page);
+
+                        err = copy_huge_page_from_user(page,
+                                                (const void __user *)src_addr,
+                                                pages_per_huge_page(h));
+                        if (unlikely(err)) {
+                                err = -EFAULT;
+                                goto out;
+                        }
+                        down_read(&dst_mm->mmap_sem);
+
+                        dst_vma = NULL;
+                        goto retry;
+                } else
+                        BUG_ON(page);
+
+                if (!err) {
+                        dst_addr += vma_hpagesize;
+                        src_addr += vma_hpagesize;
+                        copied += vma_hpagesize;
+
+                        if (fatal_signal_pending(current))
+                                err = -EINTR;
+                }
+                if (err)
+                        break;
+        }
+
+out_unlock:
+        up_read(&dst_mm->mmap_sem);
+out:
+        if (page)
+                put_page(page);
+        BUG_ON(copied < 0);
+        BUG_ON(err > 0);
+        BUG_ON(!copied && !err);
+        return copied ? copied : err;
+}
+#else /* !CONFIG_HUGETLB_PAGE */
+/* fail at build time if gcc attempts to use this */
+extern ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm,
+                                      struct vm_area_struct *dst_vma,
+                                      unsigned long dst_start,
+                                      unsigned long src_start,
+                                      unsigned long len,
+                                      bool zeropage);
+#endif /* CONFIG_HUGETLB_PAGE */
+
 static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
                                               unsigned long dst_start,
                                               unsigned long src_start,
@@ -182,6 +361,13 @@ retry:
                 goto out_unlock;
 
         /*
+         * If this is a HUGETLB vma, pass off to appropriate routine
+         */
+        if (is_vm_hugetlb_page(dst_vma))
+                return  __mcopy_atomic_hugetlb(dst_mm, dst_vma, dst_start,
+                                                src_start, len, zeropage);
+
+        /*
          * Be strict and only allow __mcopy_atomic on userfaultfd
          * registered ranges to prevent userland errors going
          * unnoticed. As far as the VM consistency is concerned, it