[Xen-devel] [PATCH v3 1/4] x86/boot: add acpi rsdp address to setup_header

[Juergen Gross <jgross@xxxxxxxx>]

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 for 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).

While documenting the new setup_header layout and protocol version
2.14 add the missing documentation of protocol version 2.13.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
V3: fix commit message and some documentation bits (Ingo Molnar)
---
 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..cec112909c35 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
+
+Protocol 2.14  (Kernel 4.16) Added acpi_rsdp_addr holding the physical
+               address of the ACPI RSDP table.
+
 **** MEMORY LAYOUT
 
 The traditional memory map for the kernel loader, used for Image or
@@ -197,6 +204,7 @@ Offset      Proto   Name            Meaning
 0258/8 2.10+   pref_address    Preferred loading address
 0260/4 2.10+   init_size       Linear memory required during initialization
 0264/4 2.11+   handover_offset Offset of handover entry point
+0268/8 2.14+   acpi_rsdp_addr  Physical address of RSDP table
 
 (1) For backwards compatibility, if the setup_sects field contains 0, the
     real value is 4.
@@ -744,6 +752,17 @@ Offset/size:       0x264/4
 
   See EFI HANDOVER PROTOCOL below for more details.
 
+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.
+
 
 **** THE IMAGE CHECKSUM
 
diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S
index 850b8762e889..4c881c850125 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 the
+                                               # ACPI RSDP table, added with
+                                               # version 2.14
+
 # End of setup header #####################################################
 
        .section ".entrytext", "ax"
diff --git a/arch/x86/include/uapi/asm/bootparam.h 
b/arch/x86/include/uapi/asm/bootparam.h
index afdd5ae0fcc4..5742e433e93e 100644
--- a/arch/x86/include/uapi/asm/bootparam.h
+++ b/arch/x86/include/uapi/asm/bootparam.h
@@ -85,6 +85,7 @@ struct setup_header {
        __u64   pref_address;
        __u32   init_size;
        __u32   handover_offset;
+       __u64   acpi_rsdp_addr;
 } __attribute__((packed));
 
 struct sys_desc_table {
-- 
2.12.3


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