[PATCH v2 3/3] dax: Support for transparent PUD pages for device DAX

[Dave Jiang <dave.jiang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>]

Adding transparent huge PUD pages support for device DAX by adding a
pud_fault handler.

Signed-off-by: Dave Jiang <dave.jiang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
---
 drivers/dax/dax.c |   48 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/drivers/dax/dax.c b/drivers/dax/dax.c
index 922ec46..b90bb30 100644
--- a/drivers/dax/dax.c
+++ b/drivers/dax/dax.c
@@ -493,6 +493,51 @@ static int __dax_dev_pmd_fault(struct dax_dev *dax_dev, struct vm_fault *vmf)
 			vmf->flags & FAULT_FLAG_WRITE);
 }
 
+#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
+static int __dax_dev_pud_fault(struct dax_dev *dax_dev, struct vm_fault *vmf)
+{
+	unsigned long pud_addr = vmf->address & PUD_MASK;
+	struct device *dev = &dax_dev->dev;
+	struct dax_region *dax_region;
+	phys_addr_t phys;
+	pgoff_t pgoff;
+	pfn_t pfn;
+
+	if (check_vma(dax_dev, vmf->vma, __func__))
+		return VM_FAULT_SIGBUS;
+
+	dax_region = dax_dev->region;
+	if (dax_region->align > PUD_SIZE) {
+		dev_dbg(dev, "%s: alignment > fault size\n", __func__);
+		return VM_FAULT_SIGBUS;
+	}
+
+	/* dax pud mappings require pfn_t_devmap() */
+	if ((dax_region->pfn_flags & (PFN_DEV|PFN_MAP)) != (PFN_DEV|PFN_MAP)) {
+		dev_dbg(dev, "%s: alignment > fault size\n", __func__);
+		return VM_FAULT_SIGBUS;
+	}
+
+	pgoff = linear_page_index(vmf->vma, pud_addr);
+	phys = pgoff_to_phys(dax_dev, pgoff, PUD_SIZE);
+	if (phys == -1) {
+		dev_dbg(dev, "%s: phys_to_pgoff(%#lx) failed\n", __func__,
+				pgoff);
+		return VM_FAULT_SIGBUS;
+	}
+
+	pfn = phys_to_pfn_t(phys, dax_region->pfn_flags);
+
+	return vmf_insert_pfn_pud(vmf->vma, vmf->address, vmf->pud, pfn,
+			vmf->flags & FAULT_FLAG_WRITE);
+}
+#else
+static int __dax_dev_pud_fault(struct dax_dev *dax_dev, struct vm_fault *vmf)
+{
+	return VM_FAULT_FALLBACK;
+}
+#endif /* !CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
+
 static int dax_dev_fault(struct vm_fault *vmf)
 {
 	int rc;
@@ -512,6 +557,9 @@ static int dax_dev_fault(struct vm_fault *vmf)
 	case FAULT_FLAG_SIZE_PMD:
 		rc = __dax_dev_pmd_fault(dax_dev, vmf);
 		break;
+	case FAULT_FLAG_SIZE_PUD:
+		rc = __dax_dev_pud_fault(dax_dev, vmf);
+		break;
 	default:
 		return VM_FAULT_FALLBACK;
 	}