xen/privcmd: improve performance of MMAPBATCH_V2

Make the IOCTL_PRIVCMD_MMAPBATCH_V2 (and older V1 version) map
multiple frames at a time rather than one at a time, despite the pages
being non-consecutive GFNs.

xen_remap_foreign_mfn_array() is added which maps an array of GFNs
(instead of a consecutive range of GFNs).

Since per-frame errors are returned in an array, privcmd must set the
MMAPBATCH_V1 error bits as part of the "report errors" phase, after
all the frames are mapped.

Migrate times are significantly improved (when using a PV toolstack
domain).  For example, for an idle 12 GiB PV guest:

        Before     After
  real  0m38.179s  0m26.868s
  user  0m15.096s  0m13.652s
  sys   0m28.988s  0m18.732s

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

arch/arm/xen/enlighten.c

@@ -53,15 +53,27 @@ EXPORT_SYMBOL_GPL(xen_platform_pci_unplug);
 
 static __read_mostly int xen_events_irq = -1;
 
-int xen_remap_domain_mfn_range(struct vm_area_struct *vma,
+int xen_remap_domain_mfn_array(struct vm_area_struct *vma,
 			       unsigned long addr,
-			       xen_pfn_t mfn, int nr,
-			       pgprot_t prot, unsigned domid,
+			       xen_pfn_t *mfn, int nr,
+			       int *err_ptr, pgprot_t prot,
+			       unsigned domid,
 			       struct page **pages)
 {
-	return xen_xlate_remap_gfn_range(vma, addr, mfn, nr,
+	return xen_xlate_remap_gfn_array(vma, addr, mfn, nr, err_ptr,
 					 prot, domid, pages);
 }
+EXPORT_SYMBOL_GPL(xen_remap_domain_mfn_array);
+
+/* Not used by XENFEAT_auto_translated guests. */
+int xen_remap_domain_mfn_range(struct vm_area_struct *vma,
+                              unsigned long addr,
+                              xen_pfn_t mfn, int nr,
+                              pgprot_t prot, unsigned domid,
+                              struct page **pages)
+{
+	return -ENOSYS;
+}
 EXPORT_SYMBOL_GPL(xen_remap_domain_mfn_range);
 
 int xen_unmap_domain_mfn_range(struct vm_area_struct *vma,

arch/x86/xen/mmu.c

@@ -2439,7 +2439,8 @@ void __init xen_hvm_init_mmu_ops(void)
 #define REMAP_BATCH_SIZE 16
 
 struct remap_data {
-	unsigned long mfn;
+	xen_pfn_t *mfn;
+	bool contiguous;
 	pgprot_t prot;
 	struct mmu_update *mmu_update;
 };
@@ -2448,7 +2449,14 @@ static int remap_area_mfn_pte_fn(pte_t *ptep, pgtable_t token,
 				 unsigned long addr, void *data)
 {
 	struct remap_data *rmd = data;
-	pte_t pte = pte_mkspecial(mfn_pte(rmd->mfn++, rmd->prot));
+	pte_t pte = pte_mkspecial(mfn_pte(*rmd->mfn, rmd->prot));
+
+	/* If we have a contigious range, just update the mfn itself,
+	   else update pointer to be "next mfn". */
+	if (rmd->contiguous)
+		(*rmd->mfn)++;
+	else
+		rmd->mfn++;
 
 	rmd->mmu_update->ptr = virt_to_machine(ptep).maddr;
 	rmd->mmu_update->val = pte_val_ma(pte);
@@ -2457,36 +2465,42 @@ static int remap_area_mfn_pte_fn(pte_t *ptep, pgtable_t token,
 	return 0;
 }
 
-int xen_remap_domain_mfn_range(struct vm_area_struct *vma,
-			       unsigned long addr,
-			       xen_pfn_t mfn, int nr,
-			       pgprot_t prot, unsigned domid,
-			       struct page **pages)
-
+static int do_remap_mfn(struct vm_area_struct *vma,
+			unsigned long addr,
+			xen_pfn_t *mfn, int nr,
+			int *err_ptr, pgprot_t prot,
+			unsigned domid,
+			struct page **pages)
 {
+	int err = 0;
 	struct remap_data rmd;
 	struct mmu_update mmu_update[REMAP_BATCH_SIZE];
-	int batch;
 	unsigned long range;
-	int err = 0;
+	int mapped = 0;
 
 	BUG_ON(!((vma->vm_flags & (VM_PFNMAP | VM_IO)) == (VM_PFNMAP | VM_IO)));
 
 	if (xen_feature(XENFEAT_auto_translated_physmap)) {
 #ifdef CONFIG_XEN_PVH
 		/* We need to update the local page tables and the xen HAP */
-		return xen_xlate_remap_gfn_range(vma, addr, mfn, nr, prot,
-						 domid, pages);
+		return xen_xlate_remap_gfn_array(vma, addr, mfn, nr, err_ptr,
+						 prot, domid, pages);
 #else
 		return -EINVAL;
 #endif
         }
 
 	rmd.mfn = mfn;
 	rmd.prot = prot;
+	/* We use the err_ptr to indicate if there we are doing a contigious
+	 * mapping or a discontigious mapping. */
+	rmd.contiguous = !err_ptr;
 
 	while (nr) {
-		batch = min(REMAP_BATCH_SIZE, nr);
+		int index = 0;
+		int done = 0;
+		int batch = min(REMAP_BATCH_SIZE, nr);
+		int batch_left = batch;
 		range = (unsigned long)batch << PAGE_SHIFT;
 
 		rmd.mmu_update = mmu_update;
@@ -2495,23 +2509,72 @@ int xen_remap_domain_mfn_range(struct vm_area_struct *vma,
 		if (err)
 			goto out;
 
-		err = HYPERVISOR_mmu_update(mmu_update, batch, NULL, domid);
-		if (err < 0)
-			goto out;
+		/* We record the error for each page that gives an error, but
+		 * continue mapping until the whole set is done */
+		do {
+			int i;
+
+			err = HYPERVISOR_mmu_update(&mmu_update[index],
+						    batch_left, &done, domid);
+
+			/*
+			 * @err_ptr may be the same buffer as @mfn, so
+			 * only clear it after each chunk of @mfn is
+			 * used.
+			 */
+			if (err_ptr) {
+				for (i = index; i < index + done; i++)
+					err_ptr[i] = 0;
+			}
+			if (err < 0) {
+				if (!err_ptr)
+					goto out;
+				err_ptr[i] = err;
+				done++; /* Skip failed frame. */
+			} else
+				mapped += done;
+			batch_left -= done;
+			index += done;
+		} while (batch_left);
 
 		nr -= batch;
 		addr += range;
+		if (err_ptr)
+			err_ptr += batch;
 	}
-
-	err = 0;
 out:
 
 	xen_flush_tlb_all();
 
-	return err;
+	return err < 0 ? err : mapped;
+}
+
+int xen_remap_domain_mfn_range(struct vm_area_struct *vma,
+			       unsigned long addr,
+			       xen_pfn_t mfn, int nr,
+			       pgprot_t prot, unsigned domid,
+			       struct page **pages)
+{
+	return do_remap_mfn(vma, addr, &mfn, nr, NULL, prot, domid, pages);
 }
 EXPORT_SYMBOL_GPL(xen_remap_domain_mfn_range);
 
+int xen_remap_domain_mfn_array(struct vm_area_struct *vma,
+			       unsigned long addr,
+			       xen_pfn_t *mfn, int nr,
+			       int *err_ptr, pgprot_t prot,
+			       unsigned domid, struct page **pages)
+{
+	/* We BUG_ON because it's a programmer error to pass a NULL err_ptr,
+	 * and the consequences later is quite hard to detect what the actual
+	 * cause of "wrong memory was mapped in".
+	 */
+	BUG_ON(err_ptr == NULL);
+	return do_remap_mfn(vma, addr, mfn, nr, err_ptr, prot, domid, pages);
+}
+EXPORT_SYMBOL_GPL(xen_remap_domain_mfn_array);
+
+
 /* Returns: 0 success */
 int xen_unmap_domain_mfn_range(struct vm_area_struct *vma,
 			       int numpgs, struct page **pages)

drivers/xen/privcmd.c

@@ -159,6 +159,40 @@ static int traverse_pages(unsigned nelem, size_t size,
 	return ret;
 }
 
+/*
+ * Similar to traverse_pages, but use each page as a "block" of
+ * data to be processed as one unit.
+ */
+static int traverse_pages_block(unsigned nelem, size_t size,
+				struct list_head *pos,
+				int (*fn)(void *data, int nr, void *state),
+				void *state)
+{
+	void *pagedata;
+	unsigned pageidx;
+	int ret = 0;
+
+	BUG_ON(size > PAGE_SIZE);
+
+	pageidx = PAGE_SIZE;
+
+	while (nelem) {
+		int nr = (PAGE_SIZE/size);
+		struct page *page;
+		if (nr > nelem)
+			nr = nelem;
+		pos = pos->next;
+		page = list_entry(pos, struct page, lru);
+		pagedata = page_address(page);
+		ret = (*fn)(pagedata, nr, state);
+		if (ret)
+			break;
+		nelem -= nr;
+	}
+
+	return ret;
+}
+
 struct mmap_mfn_state {
 	unsigned long va;
 	struct vm_area_struct *vma;
@@ -274,39 +308,25 @@ struct mmap_batch_state {
 /* auto translated dom0 note: if domU being created is PV, then mfn is
  * mfn(addr on bus). If it's auto xlated, then mfn is pfn (input to HAP).
  */
-static int mmap_batch_fn(void *data, void *state)
+static int mmap_batch_fn(void *data, int nr, void *state)
 {
 	xen_pfn_t *mfnp = data;
 	struct mmap_batch_state *st = state;
 	struct vm_area_struct *vma = st->vma;
 	struct page **pages = vma->vm_private_data;
-	struct page *cur_page = NULL;
+	struct page **cur_pages = NULL;
 	int ret;
 
 	if (xen_feature(XENFEAT_auto_translated_physmap))
-		cur_page = pages[st->index++];
+		cur_pages = &pages[st->index];
 
-	ret = xen_remap_domain_mfn_range(st->vma, st->va & PAGE_MASK, *mfnp, 1,
-					 st->vma->vm_page_prot, st->domain,
-					 &cur_page);
+	BUG_ON(nr < 0);
+	ret = xen_remap_domain_mfn_array(st->vma, st->va & PAGE_MASK, mfnp, nr,
+					 (int *)mfnp, st->vma->vm_page_prot,
+					 st->domain, cur_pages);
 
-	/* Store error code for second pass. */
-	if (st->version == 1) {
-		if (ret < 0) {
-			/*
-			 * V1 encodes the error codes in the 32bit top nibble of the
-			 * mfn (with its known limitations vis-a-vis 64 bit callers).
-			 */
-			*mfnp |= (ret == -ENOENT) ?
-						PRIVCMD_MMAPBATCH_PAGED_ERROR :
-						PRIVCMD_MMAPBATCH_MFN_ERROR;
-		}
-	} else { /* st->version == 2 */
-		*((int *) mfnp) = ret;
-	}
-
-	/* And see if it affects the global_error. */
-	if (ret < 0) {
+	/* Adjust the global_error? */
+	if (ret != nr) {
 		if (ret == -ENOENT)
 			st->global_error = -ENOENT;
 		else {
@@ -315,23 +335,35 @@ static int mmap_batch_fn(void *data, void *state)
 				st->global_error = 1;
 		}
 	}
-	st->va += PAGE_SIZE;
+	st->va += PAGE_SIZE * nr;
+	st->index += nr;
 
 	return 0;
 }
 
-static int mmap_return_errors(void *data, void *state)
+static int mmap_return_error(int err, struct mmap_batch_state *st)
 {
-	struct mmap_batch_state *st = state;
+	int ret;
 
 	if (st->version == 1) {
-		xen_pfn_t mfnp = *((xen_pfn_t *) data);
-		if (mfnp & PRIVCMD_MMAPBATCH_MFN_ERROR)
-			return __put_user(mfnp, st->user_mfn++);
-		else
+		if (err) {
+			xen_pfn_t mfn;
+
+			ret = get_user(mfn, st->user_mfn);
+			if (ret < 0)
+				return ret;
+			/*
+			 * V1 encodes the error codes in the 32bit top
+			 * nibble of the mfn (with its known
+			 * limitations vis-a-vis 64 bit callers).
+			 */
+			mfn |= (err == -ENOENT) ?
+				PRIVCMD_MMAPBATCH_PAGED_ERROR :
+				PRIVCMD_MMAPBATCH_MFN_ERROR;
+			return __put_user(mfn, st->user_mfn++);
+		} else
 			st->user_mfn++;
 	} else { /* st->version == 2 */
-		int err = *((int *) data);
 		if (err)
 			return __put_user(err, st->user_err++);
 		else
@@ -341,6 +373,21 @@ static int mmap_return_errors(void *data, void *state)
 	return 0;
 }
 
+static int mmap_return_errors(void *data, int nr, void *state)
+{
+	struct mmap_batch_state *st = state;
+	int *errs = data;
+	int i;
+	int ret;
+
+	for (i = 0; i < nr; i++) {
+		ret = mmap_return_error(errs[i], st);
+		if (ret < 0)
+			return ret;
+	}
+	return 0;
+}
+
 /* Allocate pfns that are then mapped with gmfns from foreign domid. Update
  * the vma with the page info to use later.
  * Returns: 0 if success, otherwise -errno
@@ -472,17 +519,17 @@ static long privcmd_ioctl_mmap_batch(void __user *udata, int version)
 	state.version       = version;
 
 	/* mmap_batch_fn guarantees ret == 0 */
-	BUG_ON(traverse_pages(m.num, sizeof(xen_pfn_t),
-			     &pagelist, mmap_batch_fn, &state));
+	BUG_ON(traverse_pages_block(m.num, sizeof(xen_pfn_t),
+				    &pagelist, mmap_batch_fn, &state));
 
 	up_write(&mm->mmap_sem);
 
 	if (state.global_error) {
 		/* Write back errors in second pass. */
 		state.user_mfn = (xen_pfn_t *)m.arr;
 		state.user_err = m.err;
-		ret = traverse_pages(m.num, sizeof(xen_pfn_t),
-							 &pagelist, mmap_return_errors, &state);
+		ret = traverse_pages_block(m.num, sizeof(xen_pfn_t),
+					   &pagelist, mmap_return_errors, &state);
 	} else
 		ret = 0;