Re: [PATCH V14 3/7] xen/arm: Allow hypervisor access to mem_access protected pages

[Ian Campbell <ian.campbell@citrix.com>]

On Thu, 2015-03-26 at 23:05 +0100, Tamas K Lengyel wrote:
> @@ -1209,6 +1306,10 @@ struct page_info *get_page_from_gva(struct domain *d, vaddr_t va,
>  
>  err:
>      spin_unlock(&p2m->lock);
> +
> +    if ( !page && p2m->mem_access_enabled )
> +        page = p2m_mem_access_check_and_get_page(va, flags);

Is this safe/correct to do without continuing to hold the p2m lock?

It seems like the result of gva_to_ipa in the new function perhaps ought
to be? Not sure about the p2m_get_mem_access (or does it have its own
lock? Should it?)

The case I'm thinking about is something else (grant ops etc) changing
the p2m between the first check in get_page_from_gva and this one. Worst
case would be spurious results from a race, which perhaps are tolerable?

The rest of it looked good to me.

Ian.