Andres Lagar-Cavilla
2013-Aug-21 19:44 UTC
[PATCH v4] Xen: Fix retry calls into PRIVCMD_MMAPBATCH*.
From: Andres Lagar-Cavilla <andres@lagarcavilla.org>
When a foreign mapper attempts to map guest frames that are paged out,
the mapper receives an ENOENT response and will have to try again
while a helper process pages the target frame back in.
Gating checks on PRIVCMD_MMAPBATCH* ioctl args were preventing retries
of mapping calls.
V2: Fixed autotranslated physmap mode breakage introduced by V1.
V3: Enforce full range mapping for first ioctl call on a given VMA.
V4: Shuffle logic to minimize page table walking.
Signed-off-by: Andres Lagar-Cavilla <andres@lagarcavilla.org>
---
drivers/xen/privcmd.c | 63 +++++++++++++++++++++++++++++++++++++++++-------
1 files changed, 53 insertions(+), 10 deletions(-)
diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
index f8e5dd7..f1b2462 100644
--- a/drivers/xen/privcmd.c
+++ b/drivers/xen/privcmd.c
@@ -43,9 +43,12 @@ MODULE_LICENSE("GPL");
#define PRIV_VMA_LOCKED ((void *)1)
-#ifndef HAVE_ARCH_PRIVCMD_MMAP
static int privcmd_enforce_singleshot_mapping(struct vm_area_struct *vma);
-#endif
+
+static int privcmd_enforce_singleshot_mapping_granular(
+ struct vm_area_struct *vma,
+ unsigned long addr,
+ unsigned long nr_pages);
static long privcmd_ioctl_hypercall(void __user *udata)
{
@@ -421,20 +424,34 @@ static long privcmd_ioctl_mmap_batch(void __user *udata,
int version)
vma = find_vma(mm, m.addr);
if (!vma ||
- vma->vm_ops != &privcmd_vm_ops ||
- (m.addr != vma->vm_start) ||
- ((m.addr + (nr_pages << PAGE_SHIFT)) != vma->vm_end) ||
- !privcmd_enforce_singleshot_mapping(vma)) {
- up_write(&mm->mmap_sem);
+ vma->vm_ops != &privcmd_vm_ops) {
ret = -EINVAL;
+ up_write(&mm->mmap_sem);
goto out;
}
- if (xen_feature(XENFEAT_auto_translated_physmap)) {
- ret = alloc_empty_pages(vma, m.num);
- if (ret < 0) {
+
+ /*
+ * Use singleshot mapping to enforce first-time requirements. Must map the
+ * whole VMA range, if ARM or x86-PVH must allocate balloon pages.
+ */
+ if (privcmd_enforce_singleshot_mapping(vma)) {
+ if ((m.addr != vma->vm_start) ||
+ ((m.addr + (nr_pages << PAGE_SHIFT)) != vma->vm_end) ||
+ (xen_feature(XENFEAT_auto_translated_physmap) &&
+ ((ret = alloc_empty_pages(vma, m.num)) < 0))) {
+ if (ret == 0)
+ ret = -EINVAL;
up_write(&mm->mmap_sem);
goto out;
}
+ } else {
+ if ((m.addr < vma->vm_start) ||
+ ((m.addr + (nr_pages << PAGE_SHIFT)) > vma->vm_end) ||
+ !privcmd_enforce_singleshot_mapping_granular(vma, m.addr, nr_pages)) {
+ up_write(&mm->mmap_sem);
+ ret = -EINVAL;
+ goto out;
+ }
}
state.domain = m.dom;
@@ -540,11 +557,37 @@ static int privcmd_mmap(struct file *file, struct
vm_area_struct *vma)
return 0;
}
+/*
+ * For asserting on a whole VMA. This is used by the legacy PRIVCMD_MMAP
+ * call, for MMAPBATCH* to ensure the first ioctl is called on the whole
+ * mapping range, and for autotranslated physmap mode to allocate the ballooned
+ * pages that back a mapping only once.
+ */
static int privcmd_enforce_singleshot_mapping(struct vm_area_struct *vma)
{
return !cmpxchg(&vma->vm_private_data, NULL, PRIV_VMA_LOCKED);
}
+/*
+ * For MMAPBATCH*. This allows asserting the singleshot mapping
+ * on a per pfn/pte basis. Mapping calls that fail with ENOENT
+ * can be then retried until success.
+ */
+static int enforce_singleshot_mapping_fn(pte_t *pte, struct page *pmd_page,
+ unsigned long addr, void *data)
+{
+ return pte_none(*pte) ? 0 : -EBUSY;
+}
+
+static int privcmd_enforce_singleshot_mapping_granular(
+ struct vm_area_struct *vma,
+ unsigned long addr,
+ unsigned long nr_pages)
+{
+ return apply_to_page_range(vma->vm_mm, addr, nr_pages << PAGE_SHIFT,
+ enforce_singleshot_mapping_fn, NULL) == 0;
+}
+
const struct file_operations xen_privcmd_fops = {
.owner = THIS_MODULE,
.unlocked_ioctl = privcmd_ioctl,
--
1.7.1