Re: Xen 4.7 crash

[Julien Grall <julien.grall@arm.com>]

Hi,

On 01/06/2016 22:35, Andrew Cooper wrote:
> On 01/06/2016 20:54, Aaron Cornelius wrote:
>> <snip>
>> (XEN) Xen call trace:
>> (XEN)    [<0021fdd4>] free_domheap_pages+0x1c/0x324 (PC)
>> (XEN)    [<0025b0cc>] p2m_teardown+0xa0/0x108 (LR)
>> (XEN)    [<0025b0cc>] p2m_teardown+0xa0/0x108
>> (XEN)    [<0024f668>] arch_domain_destroy+0x20/0x50
>> (XEN)    [<0024f8f0>] arch_domain_create+0x258/0x284
>> (XEN)    [<0020854c>] domain_create+0x2dc/0x510
>> (XEN)    [<00206d6c>] do_domctl+0x5b4/0x1928
>> (XEN)    [<00260130>] do_trap_hypervisor+0x1170/0x15b0
>> (XEN)    [<00263b10>] entry.o#return_from_trap+0/0x4
>> (XEN)
>> (XEN)
>> (XEN) ****************************************
>> (XEN) Panic on CPU 0:
>> (XEN) CPU0: Unexpected Trap: Data Abort
>> (XEN)
>> (XEN) ****************************************
>> (XEN)
>> (XEN) Reboot in five seconds...
>
> As for this specific crash itself,  In the case of an early error path,
> p2m->root can be NULL in p2m_teardown(), in which case
> free_domheap_pages() will fall over in a heap.  This patch should
> resolve it.

Good catch!

>
> @@ -1408,7 +1411,8 @@ void p2m_teardown(struct domain *d)
>      while ( (pg = page_list_remove_head(&p2m->pages)) )
>          free_domheap_page(pg);
>
> -    free_domheap_pages(p2m->root, P2M_ROOT_ORDER);
> +    if ( p2m->root )
> +        free_domheap_pages(p2m->root, P2M_ROOT_ORDER);
>
>      p2m->root = NULL;
>
> I would be tempted to suggest making free_domheap_pages() tolerate NULL
> pointers, except that would only be a safe thing to do if we assert that
> the order parameter is 0, which won't help this specific case.

free_xenheap_pages already tolerates NULL (even if an order != 0). Is 
there any reason to not do the same for free_domheap_pages?

Regards,

-- 
Julien Grall

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