.breaks one of my boxes (Core i3-2100), with Xen 4.1.1 (with and w/out the
23790 changset in it).
I've traced it down to the fact that I booted my dom0 without
dom0_mem=X flag with a machine that has more than 8GB. Weirdly enough
I can only reproduce this under Intel boxes.
Anyhow this patch fixes it for me.
commit e4297f5719e982d95788cd53e284a7a389eedb45
Author: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Date: Mon Sep 12 15:58:25 2011 -0400
 xen/e820: if there is not dom0_mem, don't tweak extra_pages.
 
 The patch "xen: use maximum reservation to limit amount of usable RAM"
 (d312ae878b6aed3912e1acaaf5d0b2a9d08a4f11) breaks machines that
 do not use 'dom0_mem=' argument with:
 
 reserve RAM buffer: 000000133f2e2000 - 000000133fffffff
 (XEN) mm.c:4976:d0 Global bit is set to kernel page fffff8117e
 (XEN) domain_crash_sync called from entry.S
 (XEN) Domain 0 (vcpu#0) crashed on cpu#0:
 ...
 The reason being that the last E820 entry is created using the
 'extra_pages' (which is based on how many pages have been freed).
 The mentioned git commit sets the initial value of 'extra_pages'
 using a hypercall which returns the number of pages (if dom0_mem
 has been used) or -1 otherwise. If the later we return with
 MAX_DOMAIN_PAGES as basis for calculation:
 
 return min(max_pages, MAX_DOMAIN_PAGES);
 
 and use it:
 
 extra_limit = xen_get_max_pages();
 if (extra_limit >= max_pfn)
 extra_pages = extra_limit - max_pfn;
 else
 extra_pages = 0;
 
 which means we end up with extra_pages = 128GB in PFNs (33554432)
 - 8GB in PFNs (2097152, on this specific box, can be larger or smaller),
 and then we add that value to the E820 making it:
 
 Xen: 00000000ff000000 - 0000000100000000 (reserved)
 Xen: 0000000100000000 - 000000133f2e2000 (usable)
 
 which is clearly wrong. It should look as so:
 
 Xen: 00000000ff000000 - 0000000100000000 (reserved)
 Xen: 0000000100000000 - 000000027fbda000 (usable)
 
 Naturally this problem does not present itself if dom0_mem=max:X
 is used.
 
 CC: David Vrabel <david.vrabel@xxxxxxxxxx>
 Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index c3b8d44..0632de1 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -185,16 +185,18 @@ static unsigned long __init xen_set_identity(const struct 
e820entry *list,
 return identity;
 }
 
-static unsigned long __init xen_get_max_pages(void)
+static bool __init xen_get_max_pages(unsigned long *max_pages)
 {
- unsigned long max_pages = MAX_DOMAIN_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);
+ /* If dom0_mem=X is not used, it will return -1. */
+ if (ret > 0) {
+ *max_pages = (unsigned long)min(ret, MAX_DOMAIN_PAGES);
+ return true;
+ }
+ return false;
 }
 
 /**
@@ -210,7 +212,7 @@ char * __init xen_memory_setup(void)
 int rc;
 struct xen_memory_map memmap;
 unsigned long extra_pages = 0;
- unsigned long extra_limit;
+ unsigned long extra_limit = 0;
 unsigned long identity_pages = 0;
 int i;
 int op;
@@ -305,11 +307,12 @@ char * __init xen_memory_setup(void)
 
 sanitize_e820_map(e820.map, ARRAY_SIZE(e820.map), &e820.nr_map);
 
- extra_limit = xen_get_max_pages();
- if (extra_limit >= max_pfn)
- extra_pages = extra_limit - max_pfn;
- else
- extra_pages = 0;
+ if (xen_get_max_pages(&extra_limit)) {
+ if (extra_limit >= max_pfn)
+ extra_pages = extra_limit - max_pfn;
+ else
+ extra_pages = 0;
+ }
 
 extra_pages += xen_return_unused_memory(xen_start_info->nr_pages, 
&e820);
 
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel