[PATCH 3/3] xen: use maximum reservation to limit dom0 memory

[David Vrabel <david.vrabel@citrix.com>]

Use the maximum reservation hypercall to set limit the amount of
usable dom0 memory.  This reduces the size of pages tables etc. if
dom0 is to use less memory than the maximum available.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
---
Note this requires a patched Xen that sets max_pages when creating dom0.
---
 arch/x86/xen/setup.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 3421c9e..584e7dc 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -197,7 +197,12 @@ static unsigned long __init xen_get_max_pages(void)
 	unsigned long max_pages = MAX_DOMAIN_PAGES; /* Limited by memory map. */
 
 	if (xen_initial_domain()) {
-		/* FIXME: ask hypervisor for max pages. */
+		domid_t domid = DOMID_SELF;
+		int ret;
+
+		ret = HYPERVISOR_memory_op(XENMEM_maximum_reservation, &domid);
+		if (ret > 0)
+			max_pages = ret;
 	}
 
 	return min(max_pages, MAX_DOMAIN_PAGES);
-- 
1.7.4.1