Re: [Xen-devel] [PATCH v2 1/3] x86/boot: add acpi rsdp address to setup_header

[Ingo Molnar <mingo@xxxxxxxxxx>]

* Juergen Gross <jgross@xxxxxxxx> wrote:

> Xen PVH guests receive the address of the RSDP table from Xen. In order
> to support booting a Xen PVH guest via grub2 using the standard x86
> boot entry we need a way fro grub2 to pass the RSDP address to the
> kernel.
> 
> For this purpose expand the struct setup_header to hold the physical
> address of the RSDP address. Being zero means it isn't specified and
> has to be located the legacy way (searching through low memory or
> EBDA).

s/fro
 /for

pedantry:

s/grub2
 /Grub2

> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> ---
>  Documentation/x86/boot.txt            | 19 +++++++++++++++++++
>  arch/x86/boot/header.S                |  6 +++++-
>  arch/x86/include/uapi/asm/bootparam.h |  1 +
>  3 files changed, 25 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/x86/boot.txt b/Documentation/x86/boot.txt
> index 5e9b826b5f62..a33c224797e4 100644
> --- a/Documentation/x86/boot.txt
> +++ b/Documentation/x86/boot.txt
> @@ -61,6 +61,13 @@ Protocol 2.12:     (Kernel 3.8) Added the xloadflags field 
> and extension fields
>               to struct boot_params for loading bzImage and ramdisk
>               above 4G in 64bit.
>  
> +Protocol 2.13:       (Kernel 3.14) Support 32- and 64-bit flags being set in
> +             xloadflags to support booting a 64 bit kernel from 32 bit
> +             EFI

The changelog should I think declare that we add documentation for the 2.13 
protocol iteration as well.

Also, please use a consistent spelling of '32-bit' and '64-bit' in the same 
sentence!

> +Field name:  acpi_rsdp_addr
> +Type:                write
> +Offset/size: 0x268/8
> +Protocol:    2.14+
> +
> +  This field can be set by the boot loader to tell the kernel the
> +  physical address of the ACPI RSDP table.
> +
> +  A value of 0 indicates the kernel should fall back to the standard
> +  methods to locate the RSDP (search in EBDA/low memory).

That's not the only method used: the ACPI RSDP address can also be discovered 
via 
efi.rsdp20 and efi.rsdp, both of which appear to be 32-bit values.

>  **** THE IMAGE CHECKSUM
>  
> diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S
> index 850b8762e889..e7184127f309 100644
> --- a/arch/x86/boot/header.S
> +++ b/arch/x86/boot/header.S
> @@ -300,7 +300,7 @@ _start:
>       # Part 2 of the header, from the old setup.S
>  
>               .ascii  "HdrS"          # header signature
> -             .word   0x020d          # header version number (>= 0x0105)
> +             .word   0x020e          # header version number (>= 0x0105)
>                                       # or else old loadlin-1.5 will fail)
>               .globl realmode_swtch
>  realmode_swtch:      .word   0, 0            # default_switch, SETUPSEG
> @@ -558,6 +558,10 @@ pref_address:            .quad LOAD_PHYSICAL_ADDR        
> # preferred load addr
>  init_size:           .long INIT_SIZE         # kernel initialization size
>  handover_offset:     .long 0                 # Filled in by build.c
>  
> +acpi_rsdp_addr:              .quad 0                 # 64-bit physical 
> pointer to
> +                                             # ACPI RSDP table, added with
> +                                             # version 2.14

s/pointer to ACPI RSDP table
 /pointer to the ACPI RSDP table

Also, a more fundamental question: why doesn't Xen use EFI to hand over 
hardware 
configuration details?

Thanks,

        Ingo

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