Re: [Xen-devel] [PATCH V2] arm: p2m.c bug-fix: hypervisor hang on __p2m_get_mem_access

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Wed, 2016-01-27 at 14:24 +0200, Corneliu ZUZU wrote:
> When __p2m_get_mem_access gets called, the p2m lock is already taken
> by either get_page_from_gva or p2m_get_mem_access.
> 
> Possible code paths:
> 1)    -> get_page_from_gva
>               -> p2m_mem_access_check_and_get_page
>                       -> __p2m_get_mem_access
> 2)    -> p2m_get_mem_access
>               -> __p2m_get_mem_access
> 
> In both cases if __p2m_get_mem_access subsequently gets to
> call p2m_lookup (happens if !radix_tree_lookup(...)), a hypervisor
> hang will occur, since p2m_lookup also spin-locks on the p2m lock.
> 
> This bug-fix simply replaces the p2m_lookup call from
> __p2m_get_mem_access
> with a call to __p2m_lookup.
> 
> Following Ian's suggestion, we also add an ASSERT to ensure that
> the p2m lock is taken upon __p2m_get_mem_access entry.
> 
> Signed-off-by: Corneliu ZUZU <czuzu@xxxxxxxxxxxxxxx>

Acked + applied, thanks.


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