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Re: [Xen-devel] Debian linux-image-2.6.32-4-xen-amd64 2.6.32-11 doesn't

To: Thomas Schwinge <thomas@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Debian linux-image-2.6.32-4-xen-amd64 2.6.32-11 doesn't boot with > 4 GiB; resets immediatelly, no log messages
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Wed, 28 Apr 2010 14:21:58 -0700
Cc: Ian Campbell <ijc@xxxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
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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?


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

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

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 
        return len;
-static unsigned long __init xen_return_unused_memory(const struct e820map 
+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, 
+       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";

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