diff options
| author | Andy Shevchenko <andriy.shevchenko@linux.intel.com> | 2024-11-25 12:49:14 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2024-11-25 21:40:56 +0100 |
| commit | be4ca6c53e66cb275cf0d71f32dac0c4606b9dc0 (patch) | |
| tree | 57202f5a75cf2118cc392fcd68efd96bf3e10bea /Documentation | |
| parent | c809b0d0e52d01c30066367b2952c4c4186b1047 (diff) | |
| download | lwn-be4ca6c53e66cb275cf0d71f32dac0c4606b9dc0.tar.gz lwn-be4ca6c53e66cb275cf0d71f32dac0c4606b9dc0.zip | |
x86/Documentation: Update algo in init_size description of boot protocol
The init_size description of boot protocol has an example of the runtime
start address for the compressed bzImage. For non-relocatable kernel
it relies on the pref_address value (if not 0), but for relocatable case
only pays respect to the load_addres and kernel_alignment, and it is
inaccurate for the latter. Boot loader must consider the pref_address
as the Linux kernel relocates to it before being decompressed as nicely
described in this commit message a year ago:
43b1d3e68ee7 ("kexec: Allocate kernel above bzImage's pref_address")
Due to this documentation inaccuracy some of the bootloaders (*) made a
mistake in the calculations and if kernel image is big enough, this may
lead to unbootable configurations.
*)
In particular, kexec-tools missed that and resently got a couple of
changes which will be part of v2.0.30 release. For the record,
commit 43b1d3e68ee7 only fixed the kernel kexec implementation and
also missed to update the init_size description.
While at it, make an example C-like looking as it's done elsewhere in
the document and fix indentation as presribed by the reStructuredText
specifications, so the syntax highliting will work properly.
Fixes: 43b1d3e68ee7 ("kexec: Allocate kernel above bzImage's pref_address")
Fixes: d297366ba692 ("x86: document new bzImage fields")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Link: https://lore.kernel.org/r/20241125105005.1616154-1-andriy.shevchenko@linux.intel.com
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/arch/x86/boot.rst | 17 |
1 files changed, 13 insertions, 4 deletions
diff --git a/Documentation/arch/x86/boot.rst b/Documentation/arch/x86/boot.rst index 4fd492cb4970..ad2d8ddad27f 100644 --- a/Documentation/arch/x86/boot.rst +++ b/Documentation/arch/x86/boot.rst @@ -896,10 +896,19 @@ Offset/size: 0x260/4 The kernel runtime start address is determined by the following algorithm:: - if (relocatable_kernel) - runtime_start = align_up(load_address, kernel_alignment) - else - runtime_start = pref_address + if (relocatable_kernel) { + if (load_address < pref_address) + load_address = pref_address; + runtime_start = align_up(load_address, kernel_alignment); + } else { + runtime_start = pref_address; + } + +Hence the necessary memory window location and size can be estimated by +a boot loader as:: + + memory_window_start = runtime_start; + memory_window_size = init_size; ============ =============== Field name: handover_offset |