Re: Debian linux-image-2.6.32-4-xen-amd64 2.6.32-11 doesn't boot with > 4 GiB; resets immediatelly, no log messages

[Jeremy Fitzhardinge <jeremy@goop.org>]

On 04/20/2010 04:18 AM, Thomas Schwinge wrote:
> Hello!
>
> On Sat, Apr 10, 2010 at 03:52:45PM -0700, Jeremy Fitzhardinge wrote:
>   
>> On 04/10/2010 03:13 PM, Thomas Schwinge wrote:
>>     
>>>> Normally that would be OK, because it uses:
>>>>
>>>> 	__get_user(pfn, &machine_to_phys_mapping[mfn]);
>>>>
>>>> to dereference the array.  But at this early stage, none of the kernel's
>>>> exception handlers have been set up, so this will just fault into Xen.
>>>>
>>>> It would be interesting to confirm this by building your kernel with
>>>> CONFIG_DEBUG_INFO=y in the .config, and verify that the faulting
>>>> instruction is actually this line.
>>>>     
>>>>         
>>> Bingo!
>>>       
>> Excellent.  Now I just need to work out how to do a proper manual limit
>> check on the mfn.  (I've always been a bit suspicious of this code,
>> because there's no guarantee that a random invalid mfn *won't* happen to
>> return the pfn we're looking for...)
>>     
> Any news already about this one?
>   

Does this help?

    J

From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Subject: [PATCH] xen/core: don't bother trying to free pages beyond the ones Xen gave us

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 8dc1635..9deb6ba 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -78,18 +78,24 @@ static unsigned long __init xen_release_chunk(phys_addr_t start_addr,
 	return len;
 }
 
-static unsigned long __init xen_return_unused_memory(const struct e820map *e820)
+static unsigned long __init xen_return_unused_memory(unsigned long max_pfn,
+						     const struct e820map *e820)
 {
+	phys_addr_t max_addr = PFN_PHYS(max_pfn);
 	phys_addr_t last_end = 0;
 	unsigned long released = 0;
 	int i;
 
-	for (i = 0; i < e820->nr_map; i++) {
-		released += xen_release_chunk(last_end, e820->map[i].addr);
+	for (i = 0; i < e820->nr_map && last_end < max_addr; i++) {
+		phys_addr_t end = e820->map[i].addr;
+		end = min(max_addr, end);
+
+		released += xen_release_chunk(last_end, end);
 		last_end = e820->map[i].addr + e820->map[i].size;
 	}
 
-	released += xen_release_chunk(last_end, PFN_PHYS(xen_start_info->nr_pages));
+	if (last_end < max_addr)
+		released += xen_release_chunk(last_end, max_addr);
 
 	printk(KERN_INFO "released %ld pages of unused memory\n", released);
 	return released;
@@ -129,7 +135,7 @@ char * __init xen_memory_setup(void)
 
 	sanitize_e820_map(e820.map, ARRAY_SIZE(e820.map), &e820.nr_map);
 
-	xen_return_unused_memory(&e820);
+	xen_return_unused_memory(xen_start_info->nr_pages, &e820);
 
 	return "Xen";
 }