Re: [XEN RFC PATCH 18/40] xen/arm: Keep memory nodes in dtb for NUMA when boot from EFI

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 11 Aug 2021, Wei Chen wrote:
> EFI can get memory map from EFI system table. But EFI system
> table doesn't contain memory NUMA information, EFI depends on
> ACPI SRAT or device tree memory node to parse memory blocks'
> NUMA mapping.
> 
> But in current code, when Xen is booting from EFI, it will
> delete all memory nodes in device tree. So in UEFI + DTB
> boot, we don't have numa-node-id for memory blocks any more.
> 
> So in this patch, we will keep memory nodes in device tree for
> NUMA code to parse memory numa-node-id later.
> 
> As a side effect, if we still parse boot memory information in
> early_scan_node, bootmem.info will calculate memory ranges in
> memory nodes twice. So we have to prvent early_scan_node to
> parse memory nodes in EFI boot.
> 
> As EFI APIs only can be used in Arm64, so we introduced a wrapper
> in header file to prevent #ifdef CONFIG_ARM_64/32 in code block.
> 
> Signed-off-by: Wei Chen <wei.chen@xxxxxxx>
> ---
>  xen/arch/arm/bootfdt.c      |  8 +++++++-
>  xen/arch/arm/efi/efi-boot.h | 25 -------------------------
>  xen/include/asm-arm/setup.h |  6 ++++++
>  3 files changed, 13 insertions(+), 26 deletions(-)
> 
> diff --git a/xen/arch/arm/bootfdt.c b/xen/arch/arm/bootfdt.c
> index 476e32e0f5..7df149dbca 100644
> --- a/xen/arch/arm/bootfdt.c
> +++ b/xen/arch/arm/bootfdt.c
> @@ -11,6 +11,7 @@
>  #include <xen/lib.h>
>  #include <xen/kernel.h>
>  #include <xen/init.h>
> +#include <xen/efi.h>
>  #include <xen/device_tree.h>
>  #include <xen/libfdt/libfdt.h>
>  #include <xen/sort.h>
> @@ -335,7 +336,12 @@ static int __init early_scan_node(const void *fdt,
>  {
>      int rc = 0;
>  
> -    if ( device_tree_node_matches(fdt, node, "memory") )
> +    /*
> +     * If system boot from EFI, bootinfo.mem has been set by EFI,
> +     * so we don't need to parse memory node from DTB.
> +     */
> +    if ( device_tree_node_matches(fdt, node, "memory") &&
> +         !arch_efi_enabled(EFI_BOOT) )
>          rc = process_memory_node(fdt, node, name, depth,
>                                   address_cells, size_cells, &bootinfo.mem);
>      else if ( depth == 1 && !dt_node_cmp(name, "reserved-memory") )


If we are going to use the device tree info for the numa nodes (and
related memory) does it make sense to still rely on the EFI tables for
the memory map?

I wonder if we should just use device tree for memory and ignore EFI
instead. Do you know what Linux does in this regard?