On Wed, 2016-02-03 at 13:37 +0200, Corneliu ZUZU wrote:
I just now applied a previous v2 which was already in my queue. Was this
just an accidental resend of v2 or is there some important change and this
is really a v3?
> 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 and also adds an ASSERT to ensure that the
> p2m lock
> is already taken upon __p2m_get_mem_access entry.
>
> Signed-off-by: Corneliu ZUZU <cz...@bitdefender.com>
>
> ---
> Changed since v1:
> * added p2m-lock ASSERT
> ---
> xen/arch/arm/p2m.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
> index 2190908..e8e6db4 100644
> --- a/xen/arch/arm/p2m.c
> +++ b/xen/arch/arm/p2m.c
> @@ -468,6 +468,8 @@ static int __p2m_get_mem_access(struct domain *d,
> gfn_t gfn,
> #undef ACCESS
> };
>
> + ASSERT(spin_is_locked(&p2m->lock));
> +
> /* If no setting was ever set, just return rwx. */
> if ( !p2m->mem_access_enabled )
> {
> @@ -490,7 +492,7 @@ static int __p2m_get_mem_access(struct domain *d,
> gfn_t gfn,
> * No setting was found in the Radix tree. Check if the
> * entry exists in the page-tables.
> */
> - paddr_t maddr = p2m_lookup(d, gfn_x(gfn) << PAGE_SHIFT, NULL);
> + paddr_t maddr = __p2m_lookup(d, gfn_x(gfn) << PAGE_SHIFT, NULL);
> if ( INVALID_PADDR == maddr )
> return -ESRCH;
>
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