Re: [PATCH v3 27/38] arm/p2m: Introduce p2m_lookup_attr

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

Hello Sergej,

On 16/08/2016 23:17, Sergej Proskurin wrote:
> The function "p2m_lookup_attr" allows to lookup the mfn, memory type,
> access rights, and page order corresponding to a domain's gfn.
>
> Signed-off-by: Sergej Proskurin <proskurin@sec.in.tum.de>
> ---
> Cc: Stefano Stabellini <sstabellini@kernel.org>
> Cc: Julien Grall <julien.grall@arm.com>
> ---
> v3: Change function prototype of "p2m_lookup_attr" by removing the
>     function parameter "unsigned int *mattr", as it is not needed by the
>     callers.
>
>     Change function prototype of "p2m_lookup_attr" by changing the
>     parameter of type xenmem_access_t to p2m_access_t.
> ---
>  xen/arch/arm/p2m.c        | 15 +++++++++++++++
>  xen/include/asm-arm/p2m.h | 10 ++++++++++
>  2 files changed, 25 insertions(+)
>
> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
> index 1d3df0f..cef05ed 100644
> --- a/xen/arch/arm/p2m.c
> +++ b/xen/arch/arm/p2m.c
> @@ -429,6 +429,21 @@ mfn_t p2m_lookup(struct domain *d, gfn_t gfn, p2m_type_t *t)
>      return ret;
>  }
>
> +mfn_t p2m_lookup_attr(struct p2m_domain *p2m,
> +                      gfn_t gfn,
> +                      p2m_type_t *t,
> +                      p2m_access_t *a,
> +                      unsigned int *page_order)
> +{
> +    mfn_t ret;
> +
> +    p2m_read_lock(p2m);
> +    ret = p2m_get_entry(p2m, gfn, t, a, page_order);
> +    p2m_read_unlock(p2m);
> +
> +    return ret;
> +}
> +

Why don't you directly use p2m_get_entry from altp2m code? Looking at 
the callers, there is a potential chance of deadlock because you use 
sequentially twice p2m_read_lock on the same p2m.

Give a look on how you handle h2pm in altp2m_set_mem_access.

In any case, I really don't think this function is useful as most of the 
time you will already have the lock taken.

Regards,

-- 
Julien Grall

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