Re: [Xen-devel] [PATCH] xen/setup: Don't relocate p2m/initrd over existing one

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 12/09/2016 10:50 AM, Ross Lagerwall wrote:
> When relocating the p2m/initrd, take special care not to relocate it so
> that is overlaps with the current location of the p2m/initrd. This is
> needed since the full extent of the current location is not marked as a
> reserved region in the e820 (and it shouldn't be since it is about to be
> moved).
>
> This was seen to happen to a dom0 with a large initial p2m and a small
> reserved region in the middle of the initial p2m.
>


>  
>  /*
> - * Find a free area in physical memory not yet reserved and compliant with
> - * E820 map.
> + * Find a free area in physical memory not yet reserved, compliant with the
> + * E820 map and not overlapping with the pre-allocated area.
>   * Used to relocate pre-allocated areas like initrd or p2m list which are in
>   * conflict with the to be used E820 map.
>   * In case no area is found, return 0. Otherwise return the physical address
>   * of the area which is already reserved for convenience.
>   */
> -phys_addr_t __init xen_find_free_area(phys_addr_t size)
> +phys_addr_t __init xen_find_free_area(phys_addr_t size, phys_addr_t 
> cur_start,
> +                                   phys_addr_t cur_size)
>  {
>       unsigned mapcnt;
>       phys_addr_t addr, start;
> @@ -652,7 +653,8 @@ phys_addr_t __init xen_find_free_area(phys_addr_t size)
>                       continue;
>               start = entry->addr;
>               for (addr = start; addr < start + size; addr += PAGE_SIZE) {
> -                     if (!memblock_is_reserved(addr))
> +                     if (!memblock_is_reserved(addr) &&
> +                         (addr < cur_start || addr >= cur_start + cur_size))
>                               continue;
>                       start = addr + PAGE_SIZE;
>                       if (start + size > entry->addr + entry->size)


Wouldn't this in fact make it even more likely to return pointer to the
currently allocated chunk?

If we are in [cur_start, cur_start+cur_size) then we assign this address
to 'start' and may well return it, no?

-boris



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