xen/grant-table: Avoid m2p_override during mapping

The grant mapping API does m2p_override unnecessarily: only gntdev needs it,
for blkback and future netback patches it just cause a lock contention, as
those pages never go to userspace. Therefore this series does the following:
- the original functions were renamed to __gnttab_[un]map_refs, with a new
  parameter m2p_override
- based on m2p_override either they follow the original behaviour, or just set
  the private flag and call set_phys_to_machine
- gnttab_[un]map_refs are now a wrapper to call __gnttab_[un]map_refs with
  m2p_override false
- a new function gnttab_[un]map_refs_userspace provides the old behaviour

It also removes a stray space from page.h and change ret to 0 if
XENFEAT_auto_translated_physmap, as that is the only possible return value
there.

v2:
- move the storing of the old mfn in page->index to gnttab_map_refs
- move the function header update to a separate patch

v3:
- a new approach to retain old behaviour where it needed
- squash the patches into one

v4:
- move out the common bits from m2p* functions, and pass pfn/mfn as parameter
- clear page->private before doing anything with the page, so m2p_find_override
  won't race with this

v5:
- change return value handling in __gnttab_[un]map_refs
- remove a stray space in page.h
- add detail why ret = 0 now at some places

v6:
- don't pass pfn to m2p* functions, just get it locally

Signed-off-by: Zoltan Kiss <zoltan.kiss@citrix.com>
Suggested-by: David Vrabel <david.vrabel@citrix.com>
Acked-by: David Vrabel <david.vrabel@citrix.com>
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

2 files changed, 84 insertions, 18 deletions

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 073b4a19a8b0..34a2704fbc88 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -284,8 +284,10 @@ static int map_grant_pages(struct grant_map *map)
 	}
 
 	pr_debug("map %d+%d\n", map->index, map->count);
-	err = gnttab_map_refs(map->map_ops, use_ptemod ? map->kmap_ops : NULL,
-			map->pages, map->count);
+	err = gnttab_map_refs_userspace(map->map_ops,
+					use_ptemod ? map->kmap_ops : NULL,
+					map->pages,
+					map->count);
 	if (err)
 		return err;
 
@@ -315,9 +317,10 @@ static int __unmap_grant_pages(struct grant_map *map, int offset, int pages)
 		}
 	}
 
-	err = gnttab_unmap_refs(map->unmap_ops + offset,
-			use_ptemod ? map->kmap_ops + offset : NULL, map->pages + offset,
-			pages);
+	err = gnttab_unmap_refs_userspace(map->unmap_ops + offset,
+					  use_ptemod ? map->kmap_ops + offset : NULL,
+					  map->pages + offset,
+					  pages);
 	if (err)
 		return err;
 
diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
index b84e3ab839aa..8ee13e2e45e2 100644
--- a/drivers/xen/grant-table.c
+++ b/drivers/xen/grant-table.c
@@ -928,15 +928,17 @@ void gnttab_batch_copy(struct gnttab_copy *batch, unsigned count)
 }
 EXPORT_SYMBOL_GPL(gnttab_batch_copy);
 
-int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
+int __gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
 		    struct gnttab_map_grant_ref *kmap_ops,
-		    struct page **pages, unsigned int count)
+		    struct page **pages, unsigned int count,
+		    bool m2p_override)
 {
 	int i, ret;
 	bool lazy = false;
 	pte_t *pte;
-	unsigned long mfn;
+	unsigned long mfn, pfn;
 
+	BUG_ON(kmap_ops && !m2p_override);
 	ret = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, map_ops, count);
 	if (ret)
 		return ret;
@@ -955,10 +957,12 @@ int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
 			set_phys_to_machine(map_ops[i].host_addr >> PAGE_SHIFT,
 					map_ops[i].dev_bus_addr >> PAGE_SHIFT);
 		}
-		return ret;
+		return 0;
 	}
 
-	if (!in_interrupt() && paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE) {
+	if (m2p_override &&
+	    !in_interrupt() &&
+	    paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE) {
 		arch_enter_lazy_mmu_mode();
 		lazy = true;
 	}
@@ -975,8 +979,20 @@ int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
 		} else {
 			mfn = PFN_DOWN(map_ops[i].dev_bus_addr);
 		}
-		ret = m2p_add_override(mfn, pages[i], kmap_ops ?
-				       &kmap_ops[i] : NULL);
+		pfn = page_to_pfn(pages[i]);
+
+		WARN_ON(PagePrivate(pages[i]));
+		SetPagePrivate(pages[i]);
+		set_page_private(pages[i], mfn);
+
+		pages[i]->index = pfn_to_mfn(pfn);
+		if (unlikely(!set_phys_to_machine(pfn, FOREIGN_FRAME(mfn)))) {
+			ret = -ENOMEM;
+			goto out;
+		}
+		if (m2p_override)
+			ret = m2p_add_override(mfn, pages[i], kmap_ops ?
+					       &kmap_ops[i] : NULL);
 		if (ret)
 			goto out;
 	}
@@ -987,15 +1003,32 @@ int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
 
 	return ret;
 }
+
+int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
+		    struct page **pages, unsigned int count)
+{
+	return __gnttab_map_refs(map_ops, NULL, pages, count, false);
+}
 EXPORT_SYMBOL_GPL(gnttab_map_refs);
 
-int gnttab_unmap_refs(struct gnttab_unmap_grant_ref *unmap_ops,
+int gnttab_map_refs_userspace(struct gnttab_map_grant_ref *map_ops,
+			      struct gnttab_map_grant_ref *kmap_ops,
+			      struct page **pages, unsigned int count)
+{
+	return __gnttab_map_refs(map_ops, kmap_ops, pages, count, true);
+}
+EXPORT_SYMBOL_GPL(gnttab_map_refs_userspace);
+
+int __gnttab_unmap_refs(struct gnttab_unmap_grant_ref *unmap_ops,
 		      struct gnttab_map_grant_ref *kmap_ops,
-		      struct page **pages, unsigned int count)
+		      struct page **pages, unsigned int count,
+		      bool m2p_override)
 {
 	int i, ret;
 	bool lazy = false;
+	unsigned long pfn, mfn;
 
+	BUG_ON(kmap_ops && !m2p_override);
 	ret = HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref, unmap_ops, count);
 	if (ret)
 		return ret;
@@ -1006,17 +1039,33 @@ int gnttab_unmap_refs(struct gnttab_unmap_grant_ref *unmap_ops,
 			set_phys_to_machine(unmap_ops[i].host_addr >> PAGE_SHIFT,
 					INVALID_P2M_ENTRY);
 		}
-		return ret;
+		return 0;
 	}
 
-	if (!in_interrupt() && paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE) {
+	if (m2p_override &&
+	    !in_interrupt() &&
+	    paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE) {
 		arch_enter_lazy_mmu_mode();
 		lazy = true;
 	}
 
 	for (i = 0; i < count; i++) {
-		ret = m2p_remove_override(pages[i], kmap_ops ?
-				       &kmap_ops[i] : NULL);
+		pfn = page_to_pfn(pages[i]);
+		mfn = get_phys_to_machine(pfn);
+		if (mfn == INVALID_P2M_ENTRY || !(mfn & FOREIGN_FRAME_BIT)) {
+			ret = -EINVAL;
+			goto out;
+		}
+
+		set_page_private(pages[i], INVALID_P2M_ENTRY);
+		WARN_ON(!PagePrivate(pages[i]));
+		ClearPagePrivate(pages[i]);
+		set_phys_to_machine(pfn, pages[i]->index);
+		if (m2p_override)
+			ret = m2p_remove_override(pages[i],
+						  kmap_ops ?
+						   &kmap_ops[i] : NULL,
+						  mfn);
 		if (ret)
 			goto out;
 	}
@@ -1027,8 +1076,22 @@ int gnttab_unmap_refs(struct gnttab_unmap_grant_ref *unmap_ops,
 
 	return ret;
 }
+
+int gnttab_unmap_refs(struct gnttab_unmap_grant_ref *map_ops,
+		    struct page **pages, unsigned int count)
+{
+	return __gnttab_unmap_refs(map_ops, NULL, pages, count, false);
+}
 EXPORT_SYMBOL_GPL(gnttab_unmap_refs);
 
+int gnttab_unmap_refs_userspace(struct gnttab_unmap_grant_ref *map_ops,
+				struct gnttab_map_grant_ref *kmap_ops,
+				struct page **pages, unsigned int count)
+{
+	return __gnttab_unmap_refs(map_ops, kmap_ops, pages, count, true);
+}
+EXPORT_SYMBOL_GPL(gnttab_unmap_refs_userspace);
+
 static unsigned nr_status_frames(unsigned nr_grant_frames)
 {
 	BUG_ON(grefs_per_grant_frame == 0);