[Xen-devel] [PATCH v2] xen/gntdev, gntalloc: Remove unneeded VM flags

[Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>]

The only time when granted pages need to be treated specially is when
using Xen's PTE modification for grant mappings owned by another domain
(that is, only gntdev on PV guests).  Otherwise, the area does not
require VM_DONTCOPY and VM_PFNMAP, since it can be accessed just like
any other page of RAM.

Since the vm_operations_struct close operations decrement reference
counts, a corresponding open function that increments them is required
now that it is possible to have multiple references to a single area.

Signed-off-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
---
 drivers/xen/gntalloc.c |   14 ++++++++++++--
 drivers/xen/gntdev.c   |   16 ++++++++++++++--
 2 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/drivers/xen/gntalloc.c b/drivers/xen/gntalloc.c
index a7ffdfe..f6832f4 100644
--- a/drivers/xen/gntalloc.c
+++ b/drivers/xen/gntalloc.c
@@ -427,6 +427,17 @@ static long gntalloc_ioctl(struct file *filp, unsigned int 
cmd,
        return 0;
 }
 
+static void gntalloc_vma_open(struct vm_area_struct *vma)
+{
+       struct gntalloc_gref *gref = vma->vm_private_data;
+       if (!gref)
+               return;
+
+       spin_lock(&gref_lock);
+       gref->users++;
+       spin_unlock(&gref_lock);
+}
+
 static void gntalloc_vma_close(struct vm_area_struct *vma)
 {
        struct gntalloc_gref *gref = vma->vm_private_data;
@@ -441,6 +452,7 @@ static void gntalloc_vma_close(struct vm_area_struct *vma)
 }
 
 static struct vm_operations_struct gntalloc_vmops = {
+       .open = gntalloc_vma_open,
        .close = gntalloc_vma_close,
 };
 
@@ -471,8 +483,6 @@ static int gntalloc_mmap(struct file *filp, struct 
vm_area_struct *vma)
        vma->vm_private_data = gref;
 
        vma->vm_flags |= VM_RESERVED;
-       vma->vm_flags |= VM_DONTCOPY;
-       vma->vm_flags |= VM_PFNMAP | VM_PFN_AT_MMAP;
 
        vma->vm_ops = &gntalloc_vmops;
 
diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 2faf797..69c787a 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -334,17 +334,26 @@ static int unmap_grant_pages(struct grant_map *map, int 
offset, int pages)
 
 /* ------------------------------------------------------------------ */
 
+static void gntdev_vma_open(struct vm_area_struct *vma)
+{
+       struct grant_map *map = vma->vm_private_data;
+
+       pr_debug("gntdev_vma_open %p\n", vma);
+       atomic_inc(&map->users);
+}
+
 static void gntdev_vma_close(struct vm_area_struct *vma)
 {
        struct grant_map *map = vma->vm_private_data;
 
-       pr_debug("close %p\n", vma);
+       pr_debug("gntdev_vma_close %p\n", vma);
        map->vma = NULL;
        vma->vm_private_data = NULL;
        gntdev_put_map(map);
 }
 
 static struct vm_operations_struct gntdev_vmops = {
+       .open = gntdev_vma_open,
        .close = gntdev_vma_close,
 };
 
@@ -656,7 +665,10 @@ static int gntdev_mmap(struct file *flip, struct 
vm_area_struct *vma)
 
        vma->vm_ops = &gntdev_vmops;
 
-       vma->vm_flags |= VM_RESERVED|VM_DONTCOPY|VM_DONTEXPAND|VM_PFNMAP;
+       vma->vm_flags |= VM_RESERVED|VM_DONTEXPAND;
+
+       if (use_ptemod)
+               vma->vm_flags |= VM_DONTCOPY|VM_PFNMAP;
 
        vma->vm_private_data = map;
 
-- 
1.7.3.4


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