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>

3 files changed, 90 insertions, 27 deletions

diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
index 6620b73d0490..875025f299b6 100644
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -285,8 +285,7 @@ static void free_persistent_gnts(struct xen_blkif *blkif, struct rb_root *root,
 
                 if (++segs_to_unmap == BLKIF_MAX_SEGMENTS_PER_REQUEST ||
                         !rb_next(&persistent_gnt->node)) {
-                        ret = gnttab_unmap_refs(unmap, NULL, pages,
-                                segs_to_unmap);
+                        ret = gnttab_unmap_refs(unmap, pages, segs_to_unmap);
                         BUG_ON(ret);
                         put_free_pages(blkif, pages, segs_to_unmap);
                         segs_to_unmap = 0;
@@ -321,8 +320,7 @@ static void unmap_purged_grants(struct work_struct *work)
                 pages[segs_to_unmap] = persistent_gnt->page;
 
                 if (++segs_to_unmap == BLKIF_MAX_SEGMENTS_PER_REQUEST) {
-                        ret = gnttab_unmap_refs(unmap, NULL, pages,
-                                segs_to_unmap);
+                        ret = gnttab_unmap_refs(unmap, pages, segs_to_unmap);
                         BUG_ON(ret);
                         put_free_pages(blkif, pages, segs_to_unmap);
                         segs_to_unmap = 0;
@@ -330,7 +328,7 @@ static void unmap_purged_grants(struct work_struct *work)
                 kfree(persistent_gnt);
         }
         if (segs_to_unmap > 0) {
-                ret = gnttab_unmap_refs(unmap, NULL, pages, segs_to_unmap);
+                ret = gnttab_unmap_refs(unmap, pages, segs_to_unmap);
                 BUG_ON(ret);
                 put_free_pages(blkif, pages, segs_to_unmap);
         }
@@ -670,15 +668,14 @@ static void xen_blkbk_unmap(struct xen_blkif *blkif,
                                     GNTMAP_host_map, pages[i]->handle);
                 pages[i]->handle = BLKBACK_INVALID_HANDLE;
                 if (++invcount == BLKIF_MAX_SEGMENTS_PER_REQUEST) {
-                        ret = gnttab_unmap_refs(unmap, NULL, unmap_pages,
-                                                invcount);
+                        ret = gnttab_unmap_refs(unmap, unmap_pages, invcount);
                         BUG_ON(ret);
                         put_free_pages(blkif, unmap_pages, invcount);
                         invcount = 0;
                 }
         }
         if (invcount) {
-                ret = gnttab_unmap_refs(unmap, NULL, unmap_pages, invcount);
+                ret = gnttab_unmap_refs(unmap, unmap_pages, invcount);
                 BUG_ON(ret);
                 put_free_pages(blkif, unmap_pages, invcount);
         }
@@ -740,7 +737,7 @@ again:
         }
 
         if (segs_to_map) {
-                ret = gnttab_map_refs(map, NULL, pages_to_gnt, segs_to_map);
+                ret = gnttab_map_refs(map, pages_to_gnt, segs_to_map);
                 BUG_ON(ret);
         }
 
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);