The setup_data is a bit awkward to use for extremely large data objects,
both because the setup_data header has to be adjacent to the data object
and because it has a 32-bit length field. However, it is important that
intermediate stages of the boot process have a way to identify which
chunks of memory are occupied by kernel data.
Thus we introduce a uniform way to specify such indirect data as
setup_indirect struct and SETUP_INDIRECT type.
This patch does not bump setup_header version in arch/x86/boot/header.S
because it will be followed by additional changes coming into the
Linux/x86 boot protocol.
Suggested-by: H. Peter Anvin <hpa@xxxxxxxxx>
Signed-off-by: Daniel Kiper <daniel.kiper@xxxxxxxxxx>
Reviewed-by: Eric Snowberg <eric.snowberg@xxxxxxxxxx>
Reviewed-by: Ross Philipson <ross.philipson@xxxxxxxxxx>
---
v2 - suggestions/fixes:
- add setup_indirect usage example
(suggested by Eric Snowberg and Ross Philipson).
---
Documentation/x86/boot.rst | 38 ++++++++++++++++++++++++++++++++++-
arch/x86/include/uapi/asm/bootparam.h | 11 +++++++++-
2 files changed, 47 insertions(+), 2 deletions(-)
diff --git a/Documentation/x86/boot.rst b/Documentation/x86/boot.rst
index a934a56f0516..23d3726d54fc 100644
--- a/Documentation/x86/boot.rst
+++ b/Documentation/x86/boot.rst
@@ -73,7 +73,7 @@ Protocol 2.14: BURNT BY INCORRECT COMMIT ae7e1238e68f2a472a125673ab506d49158c188
(x86/boot: Add ACPI RSDP address to setup_header)
DO NOT USE!!! ASSUME SAME AS 2.13.
-Protocol 2.15: (Kernel 5.3) Added the kernel_info.
+Protocol 2.15: (Kernel 5.3) Added the kernel_info and setup_indirect.
============= ============================================================
.. note::
@@ -827,6 +827,42 @@ Protocol: 2.09+
sure to consider the case where the linked list already contains
entries.
+ The setup_data is a bit awkward to use for extremely large data objects,
+ both because the setup_data header has to be adjacent to the data object
+ and because it has a 32-bit length field. However, it is important that
+ intermediate stages of the boot process have a way to identify which
+ chunks of memory are occupied by kernel data.
+
+ Thus setup_indirect struct and SETUP_INDIRECT type were introduced in
+ protocol 2.15.
+
+ struct setup_indirect {
+ __u32 type;
+ __u32 reserved; /* Reserved, must be set to zero. */
+ __u64 len;
+ __u64 addr;
+ };
+
+ The type member is itself simply a SETUP_* type. However, it cannot be
+ SETUP_INDIRECT since making the setup_indirect a tree structure could
+ require a lot of stack space in something that needs to parse it and
+ stack space can be limited in boot contexts.
+
+ Let's give an example how to point to SETUP_E820_EXT data using setup_indirect.
+ In this case setup_data and setup_indirect will look like this:
+
+ struct setup_data {
+ __u64 next = 0 or <addr_of_next_setup_data_struct>;
+ __u32 type = SETUP_INDIRECT;
+ __u32 len = sizeof(setup_data);
+ __u8 data[sizeof(setup_indirect)] = struct setup_indirect {
+ __u32 type = SETUP_E820_EXT;
+ __u32 reserved = 0;
+ __u64 len = <len_of_SETUP_E820_EXT_data>;
+ __u64 addr = <addr_of_SETUP_E820_EXT_data>;
+ }
+ }
+
============ ============
Field name: pref_address
Type: read (reloc)
diff --git a/arch/x86/include/uapi/asm/bootparam.h b/arch/x86/include/uapi/asm/bootparam.h
index b05318112452..aaaa17fa6ad6 100644
--- a/arch/x86/include/uapi/asm/bootparam.h
+++ b/arch/x86/include/uapi/asm/bootparam.h
@@ -2,7 +2,7 @@
#ifndef _ASM_X86_BOOTPARAM_H
#define _ASM_X86_BOOTPARAM_H
-/* setup_data types */
+/* setup_data/setup_indirect types */
#define SETUP_NONE 0
#define SETUP_E820_EXT 1
#define SETUP_DTB 2
@@ -10,6 +10,7 @@
#define SETUP_EFI 4
#define SETUP_APPLE_PROPERTIES 5
#define SETUP_JAILHOUSE 6
+#define SETUP_INDIRECT 7
/* ram_size flags */
#define RAMDISK_IMAGE_START_MASK 0x07FF
@@ -47,6 +48,14 @@ struct setup_data {
__u8 data[0];
};
+/* extensible setup indirect data node */
+struct setup_indirect {
+ __u32 type;
+ __u32 reserved; /* Reserved, must be set to zero. */
+ __u64 len;
+ __u64 addr;
+};
+
struct setup_header {
__u8 setup_sects;
__u16 root_flags;
--
2.11.0
