Re: [Xen-devel] [PATCH v2 08/10] xen/arm: keep track of reserved-memory regions

[Julien Grall <julien.grall@arm.com>]

Hi Stefano,

On 30/04/2019 22:02, Stefano Stabellini wrote:
> As we parse the device tree in Xen, keep track of the reserved-memory
> regions as they need special treatment (follow-up patches will make use
> of the stored information.)
> 
> Reuse process_memory_node to add reserved-memory regions to the
> bootinfo.reserved_mem array. Remove the warning if there is no reg in
> process_memory_node because it is a normal condition for
> reserved-memory.

And it is not a normal condition for /memory... So your argument here is not 
sufficient for me to not keep the warning here for /memory.

Rather than trying to re-purpose process_memory_node, I would prefer if you move 
out the parsing of "reg" and then provide 2 functions (one for /memory and one 
for /reserved-memory).

The parsing function will return an error if "reg" is not present, but it can be 
ignored by /reserved-memory and a warning is added for /memory.

> 
> Signed-off-by: Stefano Stabellini <stefanos@xilinx.com>
> 
> ---
> 
> Not done: create an e820-like structure on ARM.
> 
> Changes in v2:
> - call process_memory_node from process_reserved_memory_node to avoid
>    duplication
> ---
>   xen/arch/arm/bootfdt.c      | 30 ++++++++++++++++++++++--------
>   xen/include/asm-arm/setup.h |  1 +
>   2 files changed, 23 insertions(+), 8 deletions(-)
> 
> diff --git a/xen/arch/arm/bootfdt.c b/xen/arch/arm/bootfdt.c
> index b6600ab..9355a6e 100644
> --- a/xen/arch/arm/bootfdt.c
> +++ b/xen/arch/arm/bootfdt.c
> @@ -135,6 +135,8 @@ static int __init process_memory_node(const void *fdt, int node,
>       const __be32 *cell;
>       paddr_t start, size;
>       u32 reg_cells = address_cells + size_cells;
> +    struct meminfo *mem;
> +    bool reserved = (bool)data;
>   
>       if ( address_cells < 1 || size_cells < 1 )
>       {
> @@ -143,29 +145,39 @@ static int __init process_memory_node(const void *fdt, int node,
>           return 0;
>       }
>   
> +    if ( reserved )
> +        mem = &bootinfo.reserved_mem;
> +    else
> +        mem = &bootinfo.mem;
> +
>       prop = fdt_get_property(fdt, node, "reg", NULL);
>       if ( !prop )
> -    {
> -        printk("fdt: node `%s': missing `reg' property\n", name);
>           return 0;
> -    }
>   
>       cell = (const __be32 *)prop->data;
>       banks = fdt32_to_cpu(prop->len) / (reg_cells * sizeof (u32));
>   
> -    for ( i = 0; i < banks && bootinfo.mem.nr_banks < NR_MEM_BANKS; i++ )
> +    for ( i = 0; i < banks && mem->nr_banks < NR_MEM_BANKS; i++ )

As I pointed out on v1, this is pretty fragile. While ignoring /memory bank is 
fine if we have no more space, for /reserved-region this may mean using them in 
Xen allocator with the consequences we all know.

If you split the function properly, then you will be able to treat 
reserved-regions and memory differently.

Cheers,

-- 
Julien Grall

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