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Subject[PATCH] grant-table: don't set m2p override if kmap_ops is not set
Date
IMHO there's no reason to set a m2p override if the mapping is done in
kernel space, so only set the m2p override when kmap_ops is set.

When kmap_ops is not set, just set the correct p2m translation, this
avoids touching the m2p lock, reducing contention around it.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reported-by: Matt Wilson <msw@amazon.com>
Cc: Matt Wilson <msw@amazon.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Boris Ostrovsky <david.vrabel@citrix.com>
---
drivers/xen/grant-table.c | 30 ++++++++++++++++++++++++++----
1 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
index 04cdeb8..ebf7126 100644
--- a/drivers/xen/grant-table.c
+++ b/drivers/xen/grant-table.c
@@ -909,8 +909,19 @@ 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 (kmap_ops) {
+ ret = m2p_add_override(mfn, pages[i], &kmap_ops[i]);
+ } else {
+ /* No need to set the m2p override, just set p2m */
+ WARN_ON(PagePrivate(pages[i]));
+ SetPagePrivate(pages[i]);
+ set_page_private(pages[i], mfn);
+
+ if (unlikely(!set_phys_to_machine(page_to_pfn(pages[i]), FOREIGN_FRAME(mfn))))
+ ret = -ENOMEM;
+ }
+
if (ret)
return ret;
}
@@ -942,8 +953,19 @@ int gnttab_unmap_refs(struct gnttab_unmap_grant_ref *unmap_ops,
}

for (i = 0; i < count; i++) {
- ret = m2p_remove_override(pages[i], kmap_ops ?
- &kmap_ops[i] : NULL);
+ if (kmap_ops) {
+ ret = m2p_remove_override(pages[i], &kmap_ops[i]);
+ } else {
+ /* Remove p2m entry */
+ unsigned long mfn;
+
+ WARN_ON(!PagePrivate(pages[i]));
+ mfn = page_private(pages[i]);
+ ClearPagePrivate(pages[i]);
+
+ if (unlikely(!set_phys_to_machine(page_to_pfn(pages[i]), mfn)))
+ ret = -ENOMEM;
+ }
if (ret)
return ret;
}
--
1.7.7.5 (Apple Git-26)
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