arm64: Work around convergence issue with LLD linker

LLD will occasionally error out with a '__init_end does not converge'
error if INIT_IDMAP_DIR_SIZE is defined in terms of _end, as this
results in a circular dependency.

Counter this by dimensioning the initial IDMAP page tables based on a
new boundary marker 'kimage_limit', and define it such that its value
should not change as a result of the initdata segment being pushed over
a 64k segment boundary due to changes in INIT_IDMAP_DIR_SIZE, provided
that its value doesn't change by more than 2M between linker passes.

Reported-by: Arnd Bergmann <[e-mail]>
Signed-off-by: Ard Biesheuvel <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Will Deacon <[e-mail]>

arch/arm64/include/asm/kernel-pgtable.h

···
 #define INIT_DIR_SIZE (PAGE_SIZE * (EARLY_PAGES(SWAPPER_PGTABLE_LEVELS, KIMAGE_VADDR, _end, EXTRA_PAGE) \
 				    + EARLY_SEGMENT_EXTRA_PAGES))
 
-#define INIT_IDMAP_DIR_PAGES	(EARLY_PAGES(INIT_IDMAP_PGTABLE_LEVELS, KIMAGE_VADDR, _end, 1))
+#define INIT_IDMAP_DIR_PAGES	(EARLY_PAGES(INIT_IDMAP_PGTABLE_LEVELS, KIMAGE_VADDR, kimage_limit, 1))
 #define INIT_IDMAP_DIR_SIZE	((INIT_IDMAP_DIR_PAGES + EARLY_IDMAP_EXTRA_PAGES) * PAGE_SIZE)
 
 #define INIT_IDMAP_FDT_PAGES	(EARLY_PAGES(INIT_IDMAP_PGTABLE_LEVELS, 0UL, UL(MAX_FDT_SIZE), 1) - 1)

arch/arm64/kernel/image-vars.h

···
 _kernel_codesize = ABSOLUTE(__inittext_end - _text);
 #endif
 
+/*
+ * LLD will occasionally error out with a '__init_end does not converge' error
+ * if INIT_IDMAP_DIR_SIZE is defined in terms of _end, as this results in a
+ * circular dependency. Counter this by dimensioning the initial IDMAP page
+ * tables based on kimage_limit, which is defined such that its value should
+ * not change as a result of the initdata segment being pushed over a 64k
+ * segment boundary due to changes in INIT_IDMAP_DIR_SIZE, provided that its
+ * value doesn't change by more than 2M between linker passes.
+ */
+kimage_limit = ALIGN(ABSOLUTE(_end + SZ_64K), SZ_2M);
+
 #undef ASSERT
 
 #endif /* __ARM64_KERNEL_IMAGE_VARS_H */