write in 30M

hc

2024-02-20 ea08eeccae9297f7aabd2ef7f0c2517ac4549acc

 kernel/arch/x86/include/asm/boot.h
..
..
@@ -40,23 +40,40 @@
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 #ifdef CONFIG_X86_64
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 # define BOOT_STACK_SIZE	0x4000
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-# define BOOT_INIT_PGT_SIZE	(6*4096)
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-# ifdef CONFIG_RANDOMIZE_BASE
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 /*
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- * Assuming all cross the 512GB boundary:
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- * 1 page for level4
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- * (2+2)*4 pages for kernel, param, cmd_line, and randomized kernel
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- * 2 pages for first 2M (video RAM: CONFIG_X86_VERBOSE_BOOTUP).
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- * Total is 19 pages.
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+ * Used by decompressor's startup_32() to allocate page tables for identity
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+ * mapping of the 4G of RAM in 4-level paging mode:
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+ * - 1 level4 table;
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+ * - 1 level3 table;
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+ * - 4 level2 table that maps everything with 2M pages;
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+ *
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+ * The additional level5 table needed for 5-level paging is allocated from
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+ * trampoline_32bit memory.
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  */
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-#  ifdef CONFIG_X86_VERBOSE_BOOTUP
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-#   define BOOT_PGT_SIZE	(19*4096)
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-#  else /* !CONFIG_X86_VERBOSE_BOOTUP */
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-#   define BOOT_PGT_SIZE	(17*4096)
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-#  endif
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-# else /* !CONFIG_RANDOMIZE_BASE */
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-#  define BOOT_PGT_SIZE		BOOT_INIT_PGT_SIZE
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-# endif
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+# define BOOT_INIT_PGT_SIZE	(6*4096)
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+
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+/*
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+ * Total number of page tables kernel_add_identity_map() can allocate,
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+ * including page tables consumed by startup_32().
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+ *
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+ * Worst-case scenario:
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+ *  - 5-level paging needs 1 level5 table;
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+ *  - KASLR needs to map kernel, boot_params, cmdline and randomized kernel,
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+ *    assuming all of them cross 256T boundary:
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+ *    + 4*2 level4 table;
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+ *    + 4*2 level3 table;
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+ *    + 4*2 level2 table;
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+ *  - X86_VERBOSE_BOOTUP needs to map the first 2M (video RAM):
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+ *    + 1 level4 table;
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+ *    + 1 level3 table;
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+ *    + 1 level2 table;
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+ * Total: 28 tables
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+ *
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+ * Add 4 spare table in case decompressor touches anything beyond what is
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+ * accounted above. Warn if it happens.
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+ */
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+# define BOOT_PGT_SIZE_WARN	(28*4096)
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+# define BOOT_PGT_SIZE		(32*4096)
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 #else /* !CONFIG_X86_64 */
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 # define BOOT_STACK_SIZE	0x1000