Re: [Xen-devel] [PATCH v3 2/6] x86 / p2m: remove page_list check in p2m_alloc_table

[Jan Beulich <jbeulich@xxxxxxxx>]

On 05.03.2020 13:45, pdurrant@xxxxxxxx wrote:
> From: Paul Durrant <pdurrant@xxxxxxxxxx>
> 
> There does not seem to be any justification for refusing to create the
> domain's p2m table simply because it may have assigned pages.

I think there is: If any such allocation had happened before, how
would it be represented in the domain's p2m?

> Particularly
> it prevents the prior allocation of PGC_extra pages.

That's unfortunate, but will need taking care of differently then:

> --- a/xen/arch/x86/mm/p2m.c
> +++ b/xen/arch/x86/mm/p2m.c
> @@ -695,14 +695,6 @@ int p2m_alloc_table(struct p2m_domain *p2m)
>  
>      p2m_lock(p2m);
>  
> -    if ( p2m_is_hostp2m(p2m)
> -         && !page_list_empty(&d->page_list) )
> -    {
> -        P2M_ERROR("dom %d already has memory allocated\n", d->domain_id);
> -        p2m_unlock(p2m);
> -        return -EINVAL;
> -    }

Instead of checking the list to be empty, how about checking
domain_tot_pages() to return zero?

Jan

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