Re: [Xen-devel] [PATCH/RFC] Implement the memory_map hypercall

["Jun Koi" <junkoi2004@xxxxxxxxx>]

Glauber, what is this hypercall for? To map hypervisor memory from Dom0?

Thanks.
J

On 11/24/06, Glauber de Oliveira Costa <gcosta@xxxxxxxxxx> wrote:
> Keir,
>
> Here's a first draft on an implementation on the memory_map
> hypercall. I would like to have comments on this, specially at:
>
> 1) I set a new field in the domain structure, and use it whenever it's
> set to determine the maximum map. In case it's not, using max_mem will
> most probably give us a better bound than tot_pages, as it may allow us
> to balloon up later even when using tools that does not call the new
> domctl (yet to come) that sets the map limit.
>
> 2) However, as it currently breaks dom0, I'm leaving it unimplemented in
> this case, and plan to do better than that when you apply the changes
> you said you would in dom0 max_mem representation.
>
> I'm currently working on the domctl side of things, but I'd like to have
> this sorted out first.
>
> Thank you!
>
> --
> Glauber de Oliveira Costa
> Red Hat Inc.
> "Free as in Freedom"
>
>
> # HG changeset patch
> # User gcosta@xxxxxxxxxx
> # Date 1164380458 18000
> # Node ID da7aa8896ab07932160406c8b19a6ad4a61b3af7
> # Parent  47fcd5f768fef50cba2fc6dbadc7b75de55e88a5
> [XEN] Implement the memory_map hypercall
>
> It's needed to provide guests with an idea of a physical
> mapping that may differ from simply what's needed to fit
> tot_pages.
>
> Signed-off-by: Glauber de Oliveira Costa <gcosta@xxxxxxxxxx>
>
> diff -r 47fcd5f768fe -r da7aa8896ab0 xen/arch/x86/mm.c
> --- a/xen/arch/x86/mm.c Fri Nov 17 08:30:43 2006 -0500
> +++ b/xen/arch/x86/mm.c Fri Nov 24 10:00:58 2006 -0500
> @@ -2976,7 +2976,45 @@ long arch_memory_op(int op, XEN_GUEST_HA
>
>      case XENMEM_memory_map:
>      {
> -        return -ENOSYS;
> +        struct xen_memory_map memmap;
> +        struct domain *d;
> +        XEN_GUEST_HANDLE(e820entry_t) buffer;
> +        struct e820entry map;
> +
> +        if ( IS_PRIV(current->domain) )
> +            return -ENOSYS;
> +
> +        d = current->domain;
> +
> +        if ( copy_from_guest(&memmap, arg, 1) )
> +            return -EFAULT;
> +
> +        buffer = guest_handle_cast(memmap.buffer, e820entry_t);
> +        if ( unlikely(guest_handle_is_null(buffer)) )
> +            return -EFAULT;
> +
> +        memmap.nr_entries = 1;
> +
> +        /* if we were not supplied with proper information, the best we can
> +         * do is rely on the current max_pages information as a sane bound */
> +        if (d->memory_map_limit)
> +            map.size = d->memory_map_limit;
> +        else
> +            map.size = d->max_pages << PAGE_SHIFT;
> +
> +        /* 8MB slack (to balance backend allocations). */
> +        map.size += 8 << 20;
> +        map.addr = 0ULL;
> +        map.type = E820_RAM;
> +
> +        if ( copy_to_guest(arg, &memmap, 1) )
> +            return -EFAULT;
> +
> +        if ( copy_to_guest(buffer, &map, 1) < 0 )
> +            return -EFAULT;
> +
> +        return 0;
> +
>      }
>
>      case XENMEM_machine_memory_map:
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