[Xen-devel] Re: [PATCH 4/5] xen: Fix the memory registration to reflect of what is done by Xen.

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Fri, 15 Jul 2011, Anthony PERARD wrote:
> A Xen guest memory is allocated by libxc. But this memory is not
> allocated continuously, instead, it leaves the VGA IO memory space not
> allocated, same for the MMIO space (at HVM_BELOW_4G_MMIO_START of size
> HVM_BELOW_4G_MMIO_LENGTH).
> 
> So to reflect that, we do not register the physical memory for this two
> holes. But we still keep only one RAMBlock for the all RAM as it is more
> easier than have two separate blocks (1 above 4G). Also this prevent QEMU
> from use the MMIO space for a ROM.
> 
> Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
> ---
>  xen-all.c |   21 ++++++++++++++-------
>  1 files changed, 14 insertions(+), 7 deletions(-)
> 
> diff --git a/xen-all.c b/xen-all.c
> index 2c0a62d..76d5c5c 100644
> --- a/xen-all.c
> +++ b/xen-all.c
> @@ -144,6 +144,12 @@ static void xen_ram_init(ram_addr_t ram_size)
>      new_block->host = NULL;
>      new_block->offset = 0;
>      new_block->length = ram_size;
> +    if (ram_size >= HVM_BELOW_4G_RAM_END) {
> +        /* Xen does not allocate the memory continuously, and keep a hole at
> +         * HVM_BELOW_4G_MMIO_START of HVM_BELOW_4G_MMIO_LENGTH
> +         */
> +        new_block->length += HVM_BELOW_4G_MMIO_LENGTH;
> +    }
>  
>      QLIST_INSERT_HEAD(&ram_list.blocks, new_block, next);
>  
> @@ -152,20 +158,21 @@ static void xen_ram_init(ram_addr_t ram_size)
>      memset(ram_list.phys_dirty + (new_block->offset >> TARGET_PAGE_BITS),
>             0xff, new_block->length >> TARGET_PAGE_BITS);
>  
> -    if (ram_size >= 0xe0000000 ) {
> -        above_4g_mem_size = ram_size - 0xe0000000;
> -        below_4g_mem_size = 0xe0000000;
> +    if (ram_size >= HVM_BELOW_4G_RAM_END) {
> +        above_4g_mem_size = ram_size - HVM_BELOW_4G_RAM_END;
> +        below_4g_mem_size = HVM_BELOW_4G_RAM_END;
>      } else {
>          below_4g_mem_size = ram_size;
>      }
>  
> -    cpu_register_physical_memory(0, below_4g_mem_size, new_block->offset);
> -#if TARGET_PHYS_ADDR_BITS > 32
> +    cpu_register_physical_memory(0, 0xa0000, 0);
> +    /* Skip of the VGA IO memory space */
> +    cpu_register_physical_memory(0xc0000, below_4g_mem_size - 0xc0000,
> +                                 0xc0000);
 
Shouldn't we avoid registering any memory for the whole video ram area?
I mean:
    
0xa0000 - 0x100000



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