RE: static-mem preventing dom0 from booting

[Stefano Stabellini <sstabellini@kernel.org>]

+ Julien, Ian and others

On Fri, 5 Nov 2021, Stefano Stabellini wrote:
> On Fri, 5 Nov 2021, Stefano Stabellini wrote:
> > The scenario is extremely simple; you can see the full device tree
> > configuration in the attachment to my previous email.
> > 
> > - dom0
> > - dom0less domU with static-mem
> > 
> > That's it! So basically it is just a normal dom0 + dom0less domU
> > configuration, which already works fine, where I added static-mem to the
> > domU and suddenly dom0 (not the domU!) stopped working.
> 
> I did some more debugging today and I found the problem. The issue is
> that static-mem regions are added to the list of reserved_mem. However,
> reserved_mem is automatically assigned to Dom0 by default at the bottom
> of xen/arch/arm/domain_build.c:handle_node, see the second call to
> make_memory_node. Really, we shouldn't give to dom0 static-mem ranges
> meant for other domUs. E.g. the following change is sufficient to solve
> the problem:
> 
> diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> index 88a79247cb..dc609c4f0e 100644
> --- a/xen/arch/arm/domain_build.c
> +++ b/xen/arch/arm/domain_build.c
> @@ -891,6 +891,9 @@ static int __init make_memory_node(const struct domain *d,
>          u64 start = mem->bank[i].start;
>          u64 size = mem->bank[i].size;
>  
> +        if ( mem->bank[i].xen_domain )
> +            continue;
> +
>          dt_dprintk("  Bank %d: %#"PRIx64"->%#"PRIx64"\n",
>                     i, start, start + size);
>  
> However, maybe a better fix would be to purge reserved_mem of any
> xen_domain items before calling make_memory_node.
> 
> 
> I found one additional issue regarding is_domain_direct_mapped which
> doesn't return true for static-mem domains. I think we need to add a
> direct_map bool to arch_domain and set it for both dom0 and static-mem
> dom0less domUs, so that we can change the implementation of
> is_domain_direct_mapped to:
> 
> #define is_domain_direct_mapped(d) (d->arch.direct_map)
>