From d79647aea22732f39c81bbdc80931f96b46023f0 Mon Sep 17 00:00:00 2001 From: Daniel De Graaf Date: Mon, 7 Mar 2011 15:18:57 -0500 Subject: [PATCH] xen/gntdev,gntalloc: Remove unneeded VM flags 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. We are careful in the gntdev to check if we can remove those flags. The reason that we need to be careful in gntdev on PV guests is because we are not changing the PFN/MFN mapping on PV; instead, we change the application's page tables to point to the other domain's memory. This means that the vma cannot be copied without using another grant mapping hypercall; it also requires special handling on unmap, which is the reason for gntdev's dependency on the MMU notifier. For gntalloc, this is not a concern - the pages are owned by the domain using the gntalloc device, and can be mapped and unmapped in the same manner as any other page of memory. Acked-by: Ian Campbell Signed-off-by: Daniel De Graaf Signed-off-by: Konrad Rzeszutek Wilk [v2: Added in git commit "We are.." from email correspondence] --- 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 a7ffdfe19fc..f6832f46aea 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 d96d311b858..687761f65e5 100644 --- a/drivers/xen/gntdev.c +++ b/drivers/xen/gntdev.c @@ -358,17 +358,26 @@ 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, }; @@ -680,7 +689,10 @@ 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; -- 2.20.1