korg/linux
0
0
Fork 0
mirror of https://mirrors.bfsu.edu.cn/git/linux.git synced 2024-11-24 20:54:10 +08:00
Code Issues Packages Projects Releases Wiki Activity

x86/boot/compressed: Reserve more memory for page tables

Browse Source 
The decompressor has a hard limit on the number of page tables it can
allocate. This limit is defined at compile-time and will cause boot
failure if it is reached.

The kernel is very strict and calculates the limit precisely for the
worst-case scenario based on the current configuration. However, it is
easy to forget to adjust the limit when a new use-case arises. The
worst-case scenario is rarely encountered during sanity checks.

In the case of enabling 5-level paging, a use-case was overlooked. The
limit needs to be increased by one to accommodate the additional level.
This oversight went unnoticed until Aaron attempted to run the kernel
via kexec with 5-level paging and unaccepted memory enabled.

Update wost-case calculations to include 5-level paging.

To address this issue, let's allocate some extra space for page tables.
128K should be sufficient for any use-case. The logic can be simplified
by using a single value for all kernel configurations.

[ Also add a warning, should this memory run low - by Dave Hansen. ]

Fixes: 34bbb0009f ("x86/boot/compressed: Enable 5-level paging during decompression stage")
Reported-by: Aaron Lu <aaron.lu@intel.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20230915070221.10266-1-kirill.shutemov@linux.intel.com
This commit is contained in:
Kirill A. Shutemov 2023-09-15 10:02:21 +03:00 committed by Ingo Molnar
parent 7575e5a352
commit f530ee95b7
2 changed files with 40 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
arch/x86/boot/compressed/ident_map_64.c
View File

@ -59,6 +59,14 @@ static void *alloc_pgt_page(void *context)
return NULL;
}
/* Consumed more tables than expected? */
if (pages->pgt_buf_offset == BOOT_PGT_SIZE_WARN) {
debug_putstr("pgt_buf running low in " __FILE__ "\n");
debug_putstr("Need to raise BOOT_PGT_SIZE?\n");
debug_putaddr(pages->pgt_buf_offset);
debug_putaddr(pages->pgt_buf_size);
}
entry = pages->pgt_buf + pages->pgt_buf_offset;
pages->pgt_buf_offset += PAGE_SIZE;

47
arch/x86/include/asm/boot.h
View File

@ -40,23 +40,40 @@
#ifdef CONFIG_X86_64
# define BOOT_STACK_SIZE 0x4000
# define BOOT_INIT_PGT_SIZE (6*4096)
# ifdef CONFIG_RANDOMIZE_BASE
/*
* Assuming all cross the 512GB boundary:
* 1 page for level4
* (2+2)*4 pages for kernel, param, cmd_line, and randomized kernel
* 2 pages for first 2M (video RAM: CONFIG_X86_VERBOSE_BOOTUP).
* Total is 19 pages.
* Used by decompressor's startup_32() to allocate page tables for identity
* mapping of the 4G of RAM in 4-level paging mode:
* - 1 level4 table;
* - 1 level3 table;
* - 4 level2 table that maps everything with 2M pages;
*
* The additional level5 table needed for 5-level paging is allocated from
* trampoline_32bit memory.
*/
# ifdef CONFIG_X86_VERBOSE_BOOTUP
# define BOOT_PGT_SIZE (19*4096)
# else /* !CONFIG_X86_VERBOSE_BOOTUP */
# define BOOT_PGT_SIZE (17*4096)
# endif
# else /* !CONFIG_RANDOMIZE_BASE */
# define BOOT_PGT_SIZE BOOT_INIT_PGT_SIZE
# endif
# define BOOT_INIT_PGT_SIZE (6*4096)
/*
* Total number of page tables kernel_add_identity_map() can allocate,
* including page tables consumed by startup_32().
*
* Worst-case scenario:
* - 5-level paging needs 1 level5 table;
* - KASLR needs to map kernel, boot_params, cmdline and randomized kernel,
* assuming all of them cross 256T boundary:
* + 4*2 level4 table;
* + 4*2 level3 table;
* + 4*2 level2 table;
* - X86_VERBOSE_BOOTUP needs to map the first 2M (video RAM):
* + 1 level4 table;
* + 1 level3 table;
* + 1 level2 table;
* Total: 28 tables
*
* Add 4 spare table in case decompressor touches anything beyond what is
* accounted above. Warn if it happens.
*/
# define BOOT_PGT_SIZE_WARN (28*4096)
# define BOOT_PGT_SIZE (32*4096)
#else /* !CONFIG_X86_64 */
# define BOOT_STACK_SIZE 0x1000