mm/hmm: mirror hugetlbfs (snapshoting, faulting and DMA mapping)

HMM mirror is a device driver helpers to mirror range of virtual address.
It means that the process jobs running on the device can access the same
virtual address as the CPU threads of that process.  This patch adds
support for hugetlbfs mapping (ie range of virtual address that are mmap
of a hugetlbfs).

[rcampbell@nvidia.com: fix initial PFN for hugetlbfs pages]
  Link: http://lkml.kernel.org/r/20190419233536.8080-1-rcampbell@nvidia.com
Link: http://lkml.kernel.org/r/20190403193318.16478-9-jglisse@redhat.com
Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Souptick Joarder <jrdr.linux@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 109 insertions, 14 deletions

diff --git a/mm/hmm.c b/mm/hmm.c
index 0e21d3594ab6..52e40be56dc7 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -391,11 +391,13 @@ static int hmm_vma_walk_hole_(unsigned long addr, unsigned long end,
 	struct hmm_vma_walk *hmm_vma_walk = walk->private;
 	struct hmm_range *range = hmm_vma_walk->range;
 	uint64_t *pfns = range->pfns;
-	unsigned long i;
+	unsigned long i, page_size;
 
 	hmm_vma_walk->last = addr;
-	i = (addr - range->start) >> PAGE_SHIFT;
-	for (; addr < end; addr += PAGE_SIZE, i++) {
+	page_size = hmm_range_page_size(range);
+	i = (addr - range->start) >> range->page_shift;
+
+	for (; addr < end; addr += page_size, i++) {
 		pfns[i] = range->values[HMM_PFN_NONE];
 		if (fault || write_fault) {
 			int ret;
@@ -707,6 +709,69 @@ again:
 	return 0;
 }
 
+static int hmm_vma_walk_hugetlb_entry(pte_t *pte, unsigned long hmask,
+				      unsigned long start, unsigned long end,
+				      struct mm_walk *walk)
+{
+#ifdef CONFIG_HUGETLB_PAGE
+	unsigned long addr = start, i, pfn, mask, size, pfn_inc;
+	struct hmm_vma_walk *hmm_vma_walk = walk->private;
+	struct hmm_range *range = hmm_vma_walk->range;
+	struct vm_area_struct *vma = walk->vma;
+	struct hstate *h = hstate_vma(vma);
+	uint64_t orig_pfn, cpu_flags;
+	bool fault, write_fault;
+	spinlock_t *ptl;
+	pte_t entry;
+	int ret = 0;
+
+	size = 1UL << huge_page_shift(h);
+	mask = size - 1;
+	if (range->page_shift != PAGE_SHIFT) {
+		/* Make sure we are looking at full page. */
+		if (start & mask)
+			return -EINVAL;
+		if (end < (start + size))
+			return -EINVAL;
+		pfn_inc = size >> PAGE_SHIFT;
+	} else {
+		pfn_inc = 1;
+		size = PAGE_SIZE;
+	}
+
+
+	ptl = huge_pte_lock(hstate_vma(walk->vma), walk->mm, pte);
+	entry = huge_ptep_get(pte);
+
+	i = (start - range->start) >> range->page_shift;
+	orig_pfn = range->pfns[i];
+	range->pfns[i] = range->values[HMM_PFN_NONE];
+	cpu_flags = pte_to_hmm_pfn_flags(range, entry);
+	fault = write_fault = false;
+	hmm_pte_need_fault(hmm_vma_walk, orig_pfn, cpu_flags,
+			   &fault, &write_fault);
+	if (fault || write_fault) {
+		ret = -ENOENT;
+		goto unlock;
+	}
+
+	pfn = pte_pfn(entry) + ((start & mask) >> range->page_shift);
+	for (; addr < end; addr += size, i++, pfn += pfn_inc)
+		range->pfns[i] = hmm_pfn_from_pfn(range, pfn) | cpu_flags;
+	hmm_vma_walk->last = end;
+
+unlock:
+	spin_unlock(ptl);
+
+	if (ret == -ENOENT)
+		return hmm_vma_walk_hole_(addr, end, fault, write_fault, walk);
+
+	return ret;
+#else /* CONFIG_HUGETLB_PAGE */
+	return -EINVAL;
+#endif
+}
+
 static void hmm_pfns_clear(struct hmm_range *range,
 			   uint64_t *pfns,
 			   unsigned long addr,
@@ -730,6 +795,7 @@ static void hmm_pfns_special(struct hmm_range *range)
  * @mm: the mm struct for the range of virtual address
  * @start: start virtual address (inclusive)
  * @end: end virtual address (exclusive)
+ * @page_shift: expect page shift for the range
  * Returns 0 on success, -EFAULT if the address space is no longer valid
  *
  * Track updates to the CPU page table see include/linux/hmm.h
@@ -737,16 +803,20 @@ static void hmm_pfns_special(struct hmm_range *range)
 int hmm_range_register(struct hmm_range *range,
 		       struct mm_struct *mm,
 		       unsigned long start,
-		       unsigned long end)
+		       unsigned long end,
+		       unsigned page_shift)
 {
-	range->start = start & PAGE_MASK;
-	range->end = end & PAGE_MASK;
+	unsigned long mask = ((1UL << page_shift) - 1UL);
+
 	range->valid = false;
 	range->hmm = NULL;
 
-	if (range->start >= range->end)
+	if ((start & mask) || (end & mask))
+		return -EINVAL;
+	if (start >= end)
 		return -EINVAL;
 
+	range->page_shift = page_shift;
 	range->start = start;
 	range->end = end;
 
@@ -816,6 +886,7 @@ EXPORT_SYMBOL(hmm_range_unregister);
  */
 long hmm_range_snapshot(struct hmm_range *range)
 {
+	const unsigned long device_vma = VM_IO | VM_PFNMAP | VM_MIXEDMAP;
 	unsigned long start = range->start, end;
 	struct hmm_vma_walk hmm_vma_walk;
 	struct hmm *hmm = range->hmm;
@@ -832,15 +903,26 @@ long hmm_range_snapshot(struct hmm_range *range)
 			return -EAGAIN;
 
 		vma = find_vma(hmm->mm, start);
-		if (vma == NULL || (vma->vm_flags & VM_SPECIAL))
+		if (vma == NULL || (vma->vm_flags & device_vma))
 			return -EFAULT;
 
-		/* FIXME support hugetlb fs/dax */
-		if (is_vm_hugetlb_page(vma) || vma_is_dax(vma)) {
+		/* FIXME support dax */
+		if (vma_is_dax(vma)) {
 			hmm_pfns_special(range);
 			return -EINVAL;
 		}
 
+		if (is_vm_hugetlb_page(vma)) {
+			struct hstate *h = hstate_vma(vma);
+
+			if (huge_page_shift(h) != range->page_shift &&
+			    range->page_shift != PAGE_SHIFT)
+				return -EINVAL;
+		} else {
+			if (range->page_shift != PAGE_SHIFT)
+				return -EINVAL;
+		}
+
 		if (!(vma->vm_flags & VM_READ)) {
 			/*
 			 * If vma do not allow read access, then assume that it
@@ -866,6 +948,7 @@ long hmm_range_snapshot(struct hmm_range *range)
 		mm_walk.hugetlb_entry = NULL;
 		mm_walk.pmd_entry = hmm_vma_walk_pmd;
 		mm_walk.pte_hole = hmm_vma_walk_hole;
+		mm_walk.hugetlb_entry = hmm_vma_walk_hugetlb_entry;
 
 		walk_page_range(start, end, &mm_walk);
 		start = end;
@@ -884,7 +967,7 @@ EXPORT_SYMBOL(hmm_range_snapshot);
  *          then one of the following values may be returned:
  *
  *           -EINVAL  invalid arguments or mm or virtual address are in an
- *                    invalid vma (ie either hugetlbfs or device file vma).
+ *                    invalid vma (for instance device file vma).
  *           -ENOMEM: Out of memory.
  *           -EPERM:  Invalid permission (for instance asking for write and
  *                    range is read only).
@@ -905,6 +988,7 @@ EXPORT_SYMBOL(hmm_range_snapshot);
  */
 long hmm_range_fault(struct hmm_range *range, bool block)
 {
+	const unsigned long device_vma = VM_IO | VM_PFNMAP | VM_MIXEDMAP;
 	unsigned long start = range->start, end;
 	struct hmm_vma_walk hmm_vma_walk;
 	struct hmm *hmm = range->hmm;
@@ -924,15 +1008,25 @@ long hmm_range_fault(struct hmm_range *range, bool block)
 		}
 
 		vma = find_vma(hmm->mm, start);
-		if (vma == NULL || (vma->vm_flags & VM_SPECIAL))
+		if (vma == NULL || (vma->vm_flags & device_vma))
 			return -EFAULT;
 
-		/* FIXME support hugetlb fs/dax */
-		if (is_vm_hugetlb_page(vma) || vma_is_dax(vma)) {
+		/* FIXME support dax */
+		if (vma_is_dax(vma)) {
 			hmm_pfns_special(range);
 			return -EINVAL;
 		}
 
+		if (is_vm_hugetlb_page(vma)) {
+			if (huge_page_shift(hstate_vma(vma)) !=
+			    range->page_shift &&
+			    range->page_shift != PAGE_SHIFT)
+				return -EINVAL;
+		} else {
+			if (range->page_shift != PAGE_SHIFT)
+				return -EINVAL;
+		}
+
 		if (!(vma->vm_flags & VM_READ)) {
 			/*
 			 * If vma do not allow read access, then assume that it
@@ -959,6 +1053,7 @@ long hmm_range_fault(struct hmm_range *range, bool block)
 		mm_walk.hugetlb_entry = NULL;
 		mm_walk.pmd_entry = hmm_vma_walk_pmd;
 		mm_walk.pte_hole = hmm_vma_walk_hole;
+		mm_walk.hugetlb_entry = hmm_vma_walk_hugetlb_entry;
 
 		do {
 			ret = walk_page_range(start, end, &mm_walk);