Re: [Xen-devel] [v8][PATCH 10/17] hvmloader/mem_hole_alloc: skip any overlap with reserved device memory

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 01.12.14 at 10:24, <tiejun.chen@xxxxxxxxx> wrote:
> In some cases like igd_opregion_pgbase, guest will use mem_hole_alloc
> to allocate some memory to use in runtime cycle, so we alsoe need to
> make sure all reserved device memory don't overlap such a region.

While ideally this would get switched to the model outlined for
the previous two patches too, it's at least reasonable to keep
this simple allocator simple for the time being.

> --- a/tools/firmware/hvmloader/util.c
> +++ b/tools/firmware/hvmloader/util.c
> @@ -416,9 +416,29 @@ static uint32_t alloc_down = RESERVED_MEMORY_DYNAMIC_END;
>  
>  xen_pfn_t mem_hole_alloc(uint32_t nr_mfns)
>  {
> +    unsigned int i, num = hvm_get_reserved_device_memory_map();
> +    uint64_t rdm_start, rdm_end;
> +    uint32_t alloc_start, alloc_end;
> +
>      alloc_down -= nr_mfns << PAGE_SHIFT;
> +    alloc_start = alloc_down;
> +    alloc_end = alloc_start + (nr_mfns << PAGE_SHIFT);
> +    for ( i = 0; i < num; i++ )
> +    {
> +        rdm_start = (uint64_t)rdm_map[i].start_pfn << PAGE_SHIFT;
> +        rdm_end = rdm_start + ((uint64_t)rdm_map[i].nr_pages << PAGE_SHIFT);
> +        if ( check_rdm_hole_conflict((uint64_t)alloc_start,
> +                                     (uint64_t)alloc_end,

Pointless casts.

> +                                     rdm_start, rdm_end - rdm_start) )
> +        {
> +            alloc_end = rdm_start;
> +            alloc_start = alloc_end - (nr_mfns << PAGE_SHIFT);
> +            BUG_ON(alloc_up >= alloc_start);

This is redundant with the BUG_ON() below afaict. Or at least it
would be, if you would properly update allow_down (if you don't
you may end up returning the same PFN for two allocations).

> +        }
> +    }
> +
>      BUG_ON(alloc_up >= alloc_down);

Jan


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