xen/setup: Remap Xen Identity Mapped RAM

Instead of ballooning up and down dom0 memory this remaps the existing mfns
that were replaced by the identity map. The reason for this is that the
existing implementation ballooned memory up and and down which caused dom0
to have discontiguous pages. In some cases this resulted in the use of bounce
buffers which reduced network I/O performance significantly. This change will
honor the existing order of the pages with the exception of some boundary
conditions.

To do this we need to update both the Linux p2m table and the Xen m2p table.
Particular care must be taken when updating the p2m table since it's important
to limit table memory consumption and reuse the existing leaf pages which get
freed when an entire leaf page is set to the identity map. To implement this,
mapping updates are grouped into blocks with table entries getting cached
temporarily and then released.

On my test system before:
Total pages: 2105014
Total contiguous: 1640635

After:
Total pages: 2105014
Total contiguous: 2098904

Signed-off-by: Matthew Rushton <mrushton@amazon.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/arch/x86/xen/p2m.h b/arch/x86/xen/p2m.h
new file mode 100644
index 000000000000..ad8aee24ab72
--- /dev/null
+++ b/arch/x86/xen/p2m.h
@@ -0,0 +1,15 @@
+#ifndef _XEN_P2M_H
+#define _XEN_P2M_H
+
+#define P2M_PER_PAGE        (PAGE_SIZE / sizeof(unsigned long))
+#define P2M_MID_PER_PAGE    (PAGE_SIZE / sizeof(unsigned long *))
+#define P2M_TOP_PER_PAGE    (PAGE_SIZE / sizeof(unsigned long **))
+
+#define MAX_P2M_PFN         (P2M_TOP_PER_PAGE * P2M_MID_PER_PAGE * P2M_PER_PAGE)
+
+#define MAX_REMAP_RANGES    10
+
+extern unsigned long __init set_phys_range_identity(unsigned long pfn_s,
+                                      unsigned long pfn_e);
+
+#endif  /* _XEN_P2M_H */