xen/privcmd: add PRIVCMD_MMAPBATCH_V2 ioctl

PRIVCMD_MMAPBATCH_V2 extends PRIVCMD_MMAPBATCH with an additional
field for reporting the error code for every frame that could not be
mapped.  libxc prefers PRIVCMD_MMAPBATCH_V2 over PRIVCMD_MMAPBATCH.

Also expand PRIVCMD_MMAPBATCH to return appropriate error-encoding top nibble
in the mfn array.
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: Andres Lagar-Cavilla <andres@lagarcavilla.org>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

drivers/xen/privcmd.c

@@ -76,7 +76,7 @@ static void free_page_list(struct list_head *pages)
  */
 static int gather_array(struct list_head *pagelist,
 			unsigned nelem, size_t size,
-			void __user *data)
+			const void __user *data)
 {
 	unsigned pageidx;
 	void *pagedata;
@@ -246,61 +246,117 @@ struct mmap_batch_state {
 	domid_t domain;
 	unsigned long va;
 	struct vm_area_struct *vma;
-	int err;
+	/* A tristate:
+	 *      0 for no errors
+	 *      1 if at least one error has happened (and no
+	 *          -ENOENT errors have happened)
+	 *      -ENOENT if at least 1 -ENOENT has happened.
+	 */
+	int global_error;
+	/* An array for individual errors */
+	int *err;
 
-	xen_pfn_t __user *user;
+	/* User-space mfn array to store errors in the second pass for V1. */
+	xen_pfn_t __user *user_mfn;
 };
 
 static int mmap_batch_fn(void *data, void *state)
 {
 	xen_pfn_t *mfnp = data;
 	struct mmap_batch_state *st = state;
+	int ret;
+
+	ret = xen_remap_domain_mfn_range(st->vma, st->va & PAGE_MASK, *mfnp, 1,
+					 st->vma->vm_page_prot, st->domain);
 
-	if (xen_remap_domain_mfn_range(st->vma, st->va & PAGE_MASK, *mfnp, 1,
-				       st->vma->vm_page_prot, st->domain) < 0) {
-		*mfnp |= 0xf0000000U;
-		st->err++;
+	/* Store error code for second pass. */
+	*(st->err++) = ret;
+
+	/* And see if it affects the global_error. */
+	if (ret < 0) {
+		if (ret == -ENOENT)
+			st->global_error = -ENOENT;
+		else {
+			/* Record that at least one error has happened. */
+			if (st->global_error == 0)
+				st->global_error = 1;
+		}
 	}
 	st->va += PAGE_SIZE;
 
 	return 0;
 }
 
-static int mmap_return_errors(void *data, void *state)
+static int mmap_return_errors_v1(void *data, void *state)
 {
 	xen_pfn_t *mfnp = data;
 	struct mmap_batch_state *st = state;
+	int err = *(st->err++);
 
-	return put_user(*mfnp, st->user++);
+	/*
+	 * V1 encodes the error codes in the 32bit top nibble of the
+	 * mfn (with its known limitations vis-a-vis 64 bit callers).
+	 */
+	*mfnp |= (err == -ENOENT) ?
+				PRIVCMD_MMAPBATCH_PAGED_ERROR :
+				PRIVCMD_MMAPBATCH_MFN_ERROR;
+	return __put_user(*mfnp, st->user_mfn++);
 }
 
 static struct vm_operations_struct privcmd_vm_ops;
 
-static long privcmd_ioctl_mmap_batch(void __user *udata)
+static long privcmd_ioctl_mmap_batch(void __user *udata, int version)
 {
 	int ret;
-	struct privcmd_mmapbatch m;
+	struct privcmd_mmapbatch_v2 m;
 	struct mm_struct *mm = current->mm;
 	struct vm_area_struct *vma;
 	unsigned long nr_pages;
 	LIST_HEAD(pagelist);
+	int *err_array = NULL;
 	struct mmap_batch_state state;
 
 	if (!xen_initial_domain())
 		return -EPERM;
 
-	if (copy_from_user(&m, udata, sizeof(m)))
+	switch (version) {
+	case 1:
+		if (copy_from_user(&m, udata, sizeof(struct privcmd_mmapbatch)))
+			return -EFAULT;
+		/* Returns per-frame error in m.arr. */
+		m.err = NULL;
+		if (!access_ok(VERIFY_WRITE, m.arr, m.num * sizeof(*m.arr)))
 			return -EFAULT;
+		break;
+	case 2:
+		if (copy_from_user(&m, udata, sizeof(struct privcmd_mmapbatch_v2)))
+			return -EFAULT;
+		/* Returns per-frame error code in m.err. */
+		if (!access_ok(VERIFY_WRITE, m.err, m.num * (sizeof(*m.err))))
+			return -EFAULT;
+		break;
+	default:
+		return -EINVAL;
+	}
 
 	nr_pages = m.num;
 	if ((m.num <= 0) || (nr_pages > (LONG_MAX >> PAGE_SHIFT)))
 		return -EINVAL;
 
-	ret = gather_array(&pagelist, m.num, sizeof(xen_pfn_t),
-			   m.arr);
+	ret = gather_array(&pagelist, m.num, sizeof(xen_pfn_t), m.arr);
 
-	if (ret || list_empty(&pagelist))
+	if (ret)
+		goto out;
+	if (list_empty(&pagelist)) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	err_array = kcalloc(m.num, sizeof(int), GFP_KERNEL);
+	if (err_array == NULL) {
+		ret = -ENOMEM;
 		goto out;
+	}
 
 	down_write(&mm->mmap_sem);
 
@@ -318,21 +374,31 @@ static long privcmd_ioctl_mmap_batch(void __user *udata)
 	state.domain        = m.dom;
 	state.vma           = vma;
 	state.va            = m.addr;
-	state.err = 0;
+	state.global_error  = 0;
+	state.err           = err_array;
 
-	ret = traverse_pages(m.num, sizeof(xen_pfn_t),
-			     &pagelist, mmap_batch_fn, &state);
+	/* mmap_batch_fn guarantees ret == 0 */
+	BUG_ON(traverse_pages(m.num, sizeof(xen_pfn_t),
+			     &pagelist, mmap_batch_fn, &state));
 
 	up_write(&mm->mmap_sem);
 
-	if (state.err > 0) {
-		state.user = m.arr;
+	if (state.global_error && (version == 1)) {
+		/* Write back errors in second pass. */
+		state.user_mfn = (xen_pfn_t *)m.arr;
+		state.err      = err_array;
 		ret = traverse_pages(m.num, sizeof(xen_pfn_t),
-			       &pagelist,
-			       mmap_return_errors, &state);
-	}
+				     &pagelist, mmap_return_errors_v1, &state);
+	} else
+		ret = __copy_to_user(m.err, err_array, m.num * sizeof(int));
+
+	/* If we have not had any EFAULT-like global errors then set the global
+	 * error to -ENOENT if necessary. */
+	if ((ret == 0) && (state.global_error == -ENOENT))
+		ret = -ENOENT;
 
 out:
+	kfree(err_array);
 	free_page_list(&pagelist);
 
 	return ret;
@@ -354,7 +420,11 @@ static long privcmd_ioctl(struct file *file,
 		break;
 
 	case IOCTL_PRIVCMD_MMAPBATCH:
-		ret = privcmd_ioctl_mmap_batch(udata);
+		ret = privcmd_ioctl_mmap_batch(udata, 1);
+		break;
+
+	case IOCTL_PRIVCMD_MMAPBATCH_V2:
+		ret = privcmd_ioctl_mmap_batch(udata, 2);
 		break;
 
 	default:

include/xen/privcmd.h

@@ -58,13 +58,33 @@ struct privcmd_mmapbatch {
 	int num;     /* number of pages to populate */
 	domid_t dom; /* target domain */
 	__u64 addr;  /* virtual address */
-	xen_pfn_t __user *arr; /* array of mfns - top nibble set on err */
+	xen_pfn_t __user *arr; /* array of mfns - or'd with
+				  PRIVCMD_MMAPBATCH_*_ERROR on err */
+};
+
+#define PRIVCMD_MMAPBATCH_MFN_ERROR     0xf0000000U
+#define PRIVCMD_MMAPBATCH_PAGED_ERROR   0x80000000U
+
+struct privcmd_mmapbatch_v2 {
+	unsigned int num; /* number of pages to populate */
+	domid_t dom;      /* target domain */
+	__u64 addr;       /* virtual address */
+	const xen_pfn_t __user *arr; /* array of mfns */
+	int __user *err;  /* array of error codes */
 };
 
 /*
  * @cmd: IOCTL_PRIVCMD_HYPERCALL
  * @arg: &privcmd_hypercall_t
  * Return: Value returned from execution of the specified hypercall.
+ *
+ * @cmd: IOCTL_PRIVCMD_MMAPBATCH_V2
+ * @arg: &struct privcmd_mmapbatch_v2
+ * Return: 0 on success (i.e., arg->err contains valid error codes for
+ * each frame).  On an error other than a failed frame remap, -1 is
+ * returned and errno is set to EINVAL, EFAULT etc.  As an exception,
+ * if the operation was otherwise successful but any frame failed with
+ * -ENOENT, then -1 is returned and errno is set to ENOENT.
  */
 #define IOCTL_PRIVCMD_HYPERCALL					\
 	_IOC(_IOC_NONE, 'P', 0, sizeof(struct privcmd_hypercall))
@@ -72,5 +92,7 @@ struct privcmd_mmapbatch {
 	_IOC(_IOC_NONE, 'P', 2, sizeof(struct privcmd_mmap))
 #define IOCTL_PRIVCMD_MMAPBATCH					\
 	_IOC(_IOC_NONE, 'P', 3, sizeof(struct privcmd_mmapbatch))
+#define IOCTL_PRIVCMD_MMAPBATCH_V2				\
+	_IOC(_IOC_NONE, 'P', 4, sizeof(struct privcmd_mmapbatch_v2))
 
 #endif /* __LINUX_PUBLIC_PRIVCMD_H__ */