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

From: Juergen Gross
Date: Fri Dec 08 2017 - 03:36:55 EST


On 08/12/17 08:16, Ingo Molnar wrote:
>
> * 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

Okay.

>
>> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
>> Reviewed-by: Roger Pau Monnà <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!

Okay.

>
>> +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.

Sure, but this is valid for booting via EFI only.

>
>> **** 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

Okay.

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

I think Jan has answered this question quite well.


Juergen