Re: [PATCH v7u1 22/31] x86, boot: add fields to support load bzImageand ramdisk above 4G

From: Borislav Petkov
Date: Sun Jan 13 2013 - 16:42:53 EST

On Thu, Jan 03, 2013 at 04:48:42PM -0800, Yinghai Lu wrote:
> ext_ramdisk_image/size will record high 32bits for ramdisk info.
>
> xloadflags bit0 will be set if relocatable with 64bit.

Let's describe that in more detail:

"Bit 0 of xloadflags is set if we are both a 64-bit and a relocatable
kernel. In that case, it denotes that ramdisk can be loaded above 4Gb."

> Let get_ramdisk_image/size to use ext_ramdisk_image/size to get
> right positon for ramdisk.
>
> bootloader will fill value to ext_ramdisk_image/size when it load
> ramdisk above 4G.
>
> Also bootloader will check if xloadflags bit0 is set to decicde if

decide

> it could load ramdisk high above 4G.
>
> sentinel is used to make sure kernel have ext_* valid values set

The explanation of the sentinel field from "-v6" below should be
actually up here. We absolutely want to have it in the commit message
*and* in the code so that it is well documented why we've added it.

> Update header version to 2.12.
>
> -v2: add ext_cmd_line_ptr for above 4G support.
> -v3: update to xloadflags from HPA.
> -v4: use fields from bootparam instead setup_header according to HPA.
> -v5: add checking for USE_EXT_BOOT_PARAMS
> -v6: use sentinel to check if ext_* are valid suggested by HPA.
> HPA said:
> 1. add a field in the uninitialized portion, call it "sentinel";
> 2. make sure the byte position corresponding to the "sentinel" field is
> nonzero in the bzImage file;
> 3. if the kernel boots up and sentinel is nonzero, erase those fields
> that you identified as uninitialized;

Question: if the bootloader sets ext_* properly, is it going to set
sentinel to 0 so that it can signal to the code further on that ext_*
are valid?

This is kinda missing from the mechanism of the sentinel and it should
be documented too.

> -v7: change to 0x1ef instead of 0x1f0, HPA said:
> it is quite plausible that someone may (fairly sanely) start the
> copy range at 0x1f0 instead of 0x1f1

Right, all those -vX notes are all important and should *definitely* be
at least in the commit message.

> Signed-off-by: Yinghai Lu <yinghai@xxxxxxxxxx>
> Cc: Rob Landley <rob@xxxxxxxxxxx>
> Cc: Matt Fleming <matt.fleming@xxxxxxxxx>
> Cc: Gokul Caushik <caushik1@xxxxxxxxx>
> Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
> Cc: Joe Millenbach <jmillenbach@xxxxxxxxx>
> ---
> Documentation/x86/boot.txt | 15 ++++++++++++++-
> Documentation/x86/zero-page.txt | 4 ++++
> arch/x86/boot/compressed/cmdline.c | 2 ++
> arch/x86/boot/compressed/misc.c | 12 ++++++++++++
> arch/x86/boot/header.S | 12 ++++++++++--
> arch/x86/boot/setup.ld | 7 +++++++
> arch/x86/include/uapi/asm/bootparam.h | 13 ++++++++++---
> arch/x86/kernel/head64.c | 2 ++
> arch/x86/kernel/setup.c | 4 ++++
> 9 files changed, 65 insertions(+), 6 deletions(-)
>
> diff --git a/Documentation/x86/boot.txt b/Documentation/x86/boot.txt
> index 406d82d..18ca9fb 100644
> --- a/Documentation/x86/boot.txt
> +++ b/Documentation/x86/boot.txt
> @@ -57,6 +57,9 @@ Protocol 2.10: (Kernel 2.6.31) Added a protocol for relaxed alignment
> Protocol 2.11: (Kernel 3.6) Added a field for offset of EFI handover
> protocol entry point.
>
> +Protocol 2.12: (Kernel 3.9) Added three fields for loading bzImage and
> + ramdisk above 4G with 64bit in bootparam.

change to:

"Added three additional fields to bootparam used for loading bzImage and
ramdisk above 4Gb in 64-bit."

> +
> **** MEMORY LAYOUT
>
> The traditional memory map for the kernel loader, used for Image or
> @@ -182,7 +185,7 @@ Offset Proto Name Meaning
> 0230/4 2.05+ kernel_alignment Physical addr alignment required for kernel
> 0234/1 2.05+ relocatable_kernel Whether kernel is relocatable or not
> 0235/1 2.10+ min_alignment Minimum alignment, as a power of two
> -0236/2 N/A pad3 Unused
> +0236/2 2.12+ xloadflags Boot protocol option flags
> 0238/4 2.06+ cmdline_size Maximum size of the kernel command line
> 023C/4 2.07+ hardware_subarch Hardware subarchitecture
> 0240/8 2.07+ hardware_subarch_data Subarchitecture-specific data
> @@ -582,6 +585,16 @@ Protocol: 2.10+
> misaligned kernel. Therefore, a loader should typically try each
> power-of-two alignment from kernel_alignment down to this alignment.
>
> +Field name: xloadflags
> +Type: modify (obligatory)
> +Offset/size: 0x236/2
> +Protocol: 2.12+
> +
> + This field is a bitmask.
> +
> + Bit 0 (read): CAN_BE_LOADED_ABOVE_4G
> + - If 1, kernel/boot_params/cmdline/ramdisk can be above 4g,

fullstop at the
end.

> +
> Field name: cmdline_size
> Type: read
> Offset/size: 0x238/4
> diff --git a/Documentation/x86/zero-page.txt b/Documentation/x86/zero-page.txt
> index cf5437d..1140e59 100644
> --- a/Documentation/x86/zero-page.txt
> +++ b/Documentation/x86/zero-page.txt
> @@ -19,6 +19,9 @@ Offset Proto Name Meaning
> 090/010 ALL hd1_info hd1 disk parameter, OBSOLETE!!
> 0A0/010 ALL sys_desc_table System description table (struct sys_desc_table)
> 0B0/010 ALL olpc_ofw_header OLPC's OpenFirmware CIF and friends
> +0C0/004 ALL ext_ramdisk_image ramdisk_image high 32bits
> +0C4/004 ALL ext_ramdisk_size ramdisk_size high 32bits
> +0C8/004 ALL ext_cmd_line_ptr cmd_line_ptr high 32bits
> 140/080 ALL edid_info Video mode setup (struct edid_info)
> 1C0/020 ALL efi_info EFI 32 information (struct efi_info)
> 1E0/004 ALL alk_mem_k Alternative mem check, in KB
> @@ -27,6 +30,7 @@ Offset Proto Name Meaning
> 1E9/001 ALL eddbuf_entries Number of entries in eddbuf (below)
> 1EA/001 ALL edd_mbr_sig_buf_entries Number of entries in edd_mbr_sig_buffer
> (below)
> +1EF/001 ALL sentinel 0: states _ext_* fields are valid
> 290/040 ALL edd_mbr_sig_buffer EDD MBR signatures
> 2D0/A00 ALL e820_map E820 memory map table
> (array of struct e820entry)
> diff --git a/arch/x86/boot/compressed/cmdline.c b/arch/x86/boot/compressed/cmdline.c
> index b4c913c..bffd73b 100644
> --- a/arch/x86/boot/compressed/cmdline.c
> +++ b/arch/x86/boot/compressed/cmdline.c
> @@ -17,6 +17,8 @@ static unsigned long get_cmd_line_ptr(void)
> {
> unsigned long cmd_line_ptr = real_mode->hdr.cmd_line_ptr;
>
> + cmd_line_ptr |= (u64)real_mode->ext_cmd_line_ptr << 32;
> +
> return cmd_line_ptr;
> }

On 32-bit, this unsigned long cmd_line_ptr is 4 bytes and the OR doesn't
have any effect on the final result. You probably want to do:

#ifdef CONFIG_64BIT
cmd_line_ptr |= (u64)real_mode->ext_cmd_line_ptr << 32;
#endif

right?

Or instead look at ->sentinel to know whether the ext_* fields are valid
or not, and save yourself the OR if not.

> int cmdline_find_option(const char *option, char *buffer, int bufsize)
> diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
> index 88f7ff6..f714576 100644
> --- a/arch/x86/boot/compressed/misc.c
> +++ b/arch/x86/boot/compressed/misc.c
> @@ -318,6 +318,16 @@ static void parse_elf(void *output)
> free(phdrs);
> }
>
> +static void sanitize_real_mode(struct boot_params *real_mode)
> +{
> + if (real_mode->sentinel) {
> + /* ext_* fields in boot_params are not valid, clear them */
> + real_mode->ext_ramdisk_image = 0;
> + real_mode->ext_ramdisk_size = 0;
> + real_mode->ext_cmd_line_ptr = 0;
> + }
> +}
> +
> asmlinkage void decompress_kernel(void *rmode, memptr heap,
> unsigned char *input_data,
> unsigned long input_len,
> @@ -325,6 +335,8 @@ asmlinkage void decompress_kernel(void *rmode, memptr heap,
> {
> real_mode = rmode;
>
> + sanitize_real_mode(real_mode);
> +
> if (real_mode->screen_info.orig_video_mode == 7) {
> vidmem = (char *) 0xb0000;
> vidport = 0x3b4;
> diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S
> index 8c132a6..0d5790f 100644
> --- a/arch/x86/boot/header.S
> +++ b/arch/x86/boot/header.S
> @@ -279,7 +279,7 @@ _start:
> # Part 2 of the header, from the old setup.S
>
> .ascii "HdrS" # header signature
> - .word 0x020b # header version number (>= 0x0105)
> + .word 0x020c # header version number (>= 0x0105)
> # or else old loadlin-1.5 will fail)
> .globl realmode_swtch
> realmode_swtch: .word 0, 0 # default_switch, SETUPSEG
> @@ -369,7 +369,15 @@ relocatable_kernel: .byte 1
> relocatable_kernel: .byte 0
> #endif
> min_alignment: .byte MIN_KERNEL_ALIGN_LG2 # minimum alignment
> -pad3: .word 0
> +
> +xloadflags:
> +CAN_BE_LOADED_ABOVE_4G = 1 # If set, the kernel/boot_param/
> + # ramdisk could be loaded above 4g
> +#if defined(CONFIG_X86_64) && defined(CONFIG_RELOCATABLE)
> + .word CAN_BE_LOADED_ABOVE_4G
> +#else
> + .word 0
> +#endif
>
> cmdline_size: .long COMMAND_LINE_SIZE-1 #length of the command line,
> #added with boot protocol
> diff --git a/arch/x86/boot/setup.ld b/arch/x86/boot/setup.ld
> index 03c0683..9333d37 100644
> --- a/arch/x86/boot/setup.ld
> +++ b/arch/x86/boot/setup.ld
> @@ -13,6 +13,13 @@ SECTIONS
> .bstext : { *(.bstext) }
> .bsdata : { *(.bsdata) }
>
> + /* sentinel: make sure if boot_params from bootloader is right */

This should say:

/*
* The bootloader signals the validity of the three ext_* boot params with this.
*/

> + . = 495;
> + .sentinel : {
> + sentinel = .;
> + BYTE(0xff);
> + }
> +
> . = 497;
> .header : { *(.header) }
> .entrytext : { *(.entrytext) }
> diff --git a/arch/x86/include/uapi/asm/bootparam.h b/arch/x86/include/uapi/asm/bootparam.h
> index 92862cd..3d8ed8f 100644
> --- a/arch/x86/include/uapi/asm/bootparam.h
> +++ b/arch/x86/include/uapi/asm/bootparam.h
> @@ -58,7 +58,9 @@ struct setup_header {
> __u32 initrd_addr_max;
> __u32 kernel_alignment;
> __u8 relocatable_kernel;
> - __u8 _pad2[3];
> + __u8 min_alignment;

Hehe, this is actually a minor bugfix because min_alignment was only
defined in header.S but was _pad2[0] in the struct definition.

> + __u16 xloadflags;
> +#define CAN_BE_LOADED_ABOVE_4G (1<<0)
> __u32 cmdline_size;
> __u32 hardware_subarch;
> __u64 hardware_subarch_data;
> @@ -106,7 +108,10 @@ struct boot_params {
> __u8 hd1_info[16]; /* obsolete! */ /* 0x090 */
> struct sys_desc_table sys_desc_table; /* 0x0a0 */
> struct olpc_ofw_header olpc_ofw_header; /* 0x0b0 */
> - __u8 _pad4[128]; /* 0x0c0 */
> + __u32 ext_ramdisk_image; /* 0x0c0 */
> + __u32 ext_ramdisk_size; /* 0x0c4 */
> + __u32 ext_cmd_line_ptr; /* 0x0c8 */
> + __u8 _pad4[116]; /* 0x0cc */
> struct edid_info edid_info; /* 0x140 */
> struct efi_info efi_info; /* 0x1c0 */
> __u32 alt_mem_k; /* 0x1e0 */
> @@ -115,7 +120,9 @@ struct boot_params {
> __u8 eddbuf_entries; /* 0x1e9 */
> __u8 edd_mbr_sig_buf_entries; /* 0x1ea */
> __u8 kbd_status; /* 0x1eb */
> - __u8 _pad6[5]; /* 0x1ec */
> + __u8 _pad5[3]; /* 0x1ec */
> + __u8 sentinel; /* 0x1ef */
> + __u8 _pad6[1]; /* 0x1f0 */

This needs the -v7 explanation from above as a comment here or somewhere
around here, for why we've chosen 0x1ef offset.

> struct setup_header hdr; /* setup header */ /* 0x1f1 */
> __u8 _pad7[0x290-0x1f1-sizeof(struct setup_header)];
> __u32 edd_mbr_sig_buffer[EDD_MBR_SIG_MAX]; /* 0x290 */
> diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
> index 316e7b2..e63d29a 100644
> --- a/arch/x86/kernel/head64.c
> +++ b/arch/x86/kernel/head64.c
> @@ -115,6 +115,8 @@ static unsigned long get_cmd_line_ptr(void)
> {
> unsigned long cmd_line_ptr = boot_params.hdr.cmd_line_ptr;
>
> + cmd_line_ptr |= (u64)boot_params.ext_cmd_line_ptr << 32;
> +
> return cmd_line_ptr;

Ditto as above for get_cmd_line_ptr in compressed/...

> }
>
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index 644a123..2509efa 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -298,12 +298,16 @@ static u64 __init get_ramdisk_image(void)
> {
> u64 ramdisk_image = boot_params.hdr.ramdisk_image;
>
> + ramdisk_image |= (u64)boot_params.ext_ramdisk_image << 32;
> +
> return ramdisk_image;
> }
> static u64 __init get_ramdisk_size(void)
> {
> u64 ramdisk_size = boot_params.hdr.ramdisk_size;
>
> + ramdisk_size |= (u64)boot_params.ext_ramdisk_size << 32;
> +
> return ramdisk_size;

Thanks.

--
Regards/Gruss,
Boris.

Sent from a fat crate under my desk. Formatting is fine.
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