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Subject[PATCH v3] xen/grant-table: Avoid m2p_override during mapping
Date
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

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

Signed-off-by: Zoltan Kiss <zoltan.kiss@citrix.com>
Suggested-by: David Vrabel <david.vrabel@citrix.com>
---
drivers/block/xen-blkback/blkback.c | 15 +++----
drivers/xen/gntdev.c | 13 +++---
drivers/xen/grant-table.c | 81 +++++++++++++++++++++++++++++------
include/xen/grant_table.h | 8 +++-
4 files changed, 87 insertions(+), 30 deletions(-)

diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
index 6620b73..875025f 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 e41c79c..e652c0e 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 aa846a4..87ded60 100644
--- a/drivers/xen/grant-table.c
+++ b/drivers/xen/grant-table.c
@@ -880,15 +880,17 @@ 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;

+ BUG_ON(kmap_ops && !m2p_override);
ret = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, map_ops, count);
if (ret)
return ret;
@@ -907,10 +909,12 @@ 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;
}
@@ -927,8 +931,18 @@ 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);
+ if (m2p_override)
+ ret = m2p_add_override(mfn, pages[i], kmap_ops ?
+ &kmap_ops[i] : NULL);
+ else {
+ unsigned long 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))))
+ return -ENOMEM;
+ }
if (ret)
goto out;
}
@@ -937,17 +951,33 @@ int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
if (lazy)
arch_leave_lazy_mmu_mode();

- return ret;
+ return 0;
+}
+
+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;

+ BUG_ON(kmap_ops && !m2p_override);
ret = HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref, unmap_ops, count);
if (ret)
return ret;
@@ -958,17 +988,26 @@ 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);
+ if (m2p_override)
+ ret = m2p_remove_override(pages[i], kmap_ops ?
+ &kmap_ops[i] : NULL);
+ else {
+ unsigned long pfn = page_to_pfn(pages[i]);
+ WARN_ON(!PagePrivate(pages[i]));
+ ClearPagePrivate(pages[i]);
+ set_phys_to_machine(pfn, pages[i]->index);
+ }
if (ret)
goto out;
}
@@ -977,10 +1016,24 @@ int gnttab_unmap_refs(struct gnttab_unmap_grant_ref *unmap_ops,
if (lazy)
arch_leave_lazy_mmu_mode();

- return ret;
+ return 0;
+}
+
+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);
diff --git a/include/xen/grant_table.h b/include/xen/grant_table.h
index 694dcaf..9a919b1 100644
--- a/include/xen/grant_table.h
+++ b/include/xen/grant_table.h
@@ -184,11 +184,15 @@ unsigned int gnttab_max_grant_frames(void);
#define gnttab_map_vaddr(map) ((void *)(map.host_virt_addr))

int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
- struct gnttab_map_grant_ref *kmap_ops,
struct page **pages, unsigned int count);
+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);
int gnttab_unmap_refs(struct gnttab_unmap_grant_ref *unmap_ops,
- struct gnttab_map_grant_ref *kunmap_ops,
struct page **pages, unsigned int count);
+int gnttab_unmap_refs_userspace(struct gnttab_unmap_grant_ref *unmap_ops,
+ struct gnttab_map_grant_ref *kunmap_ops,
+ struct page **pages, unsigned int count);

/* Perform a batch of grant map/copy operations. Retry every batch slot
* for which the hypervisor returns GNTST_eagain. This is typically due

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