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c2689266e5
microblaze handles TLB misses in software, and the handler builds the address of the L1 entry by ORing the index into the page directory base instead of adding it (hw_exception_handler.S): bsrli r5, r3, PGDIR_SHIFT - 2 andi r5, r5, PAGE_SIZE - 4 /* Assume pgdir aligned on 4K boundary, no need for "andi r4,r4,0xfffff003" */ or r4, r4, r5 lwi r4, r4, 0 /* Get L1 entry */ The index is masked to the low 12 bits, so the OR only works if those bits of the base are zero -- which is exactly the assumption the comment states and the reason the masking of the base can be skipped. swapper_pg_dir had no alignment directive of its own. It was aligned because it followed empty_zero_page in head.S, and that one carried the .align 12: .section .data .global empty_zero_page .align 12 empty_zero_page: .space PAGE_SIZE .global swapper_pg_dir swapper_pg_dir: .space PAGE_SIZE Commit6215d9f447("arch, mm: consolidate empty_zero_page") removed empty_zero_page from head.S, and with it the .align 12 that -- despite sitting next to empty_zero_page -- was what page aligned swapper_pg_dir. Since then swapper_pg_dir lands wherever .data happens to put it, its low bits are no longer zero, and every kernel TLB miss ORs the index into a base with a nonzero offset. The resulting L1 lookups read the wrong words, no valid translation is ever installed, and the kernel spins in exceptions long before it can print anything. On qemu-system-microblazeel (petalogix-s3adsp1800) the console stays completely silent at 100% CPU; there is no oops and no guest error reported by qemu, which makes this awkward to diagnose. Give swapper_pg_dir the alignment it requires, rather than relying on a neighbour to provide it. microblaze has no noMMU variant left in mainline -- CONFIG_MMU is def_bool y and mmu_defconfig is the only defconfig -- so this is not a corner case: every mainline microblaze kernel since v7.1-rc1 fails to boot, including the v7.1 release. v7.0: swapper_pg_dir = 0xc05fd000 (aligned) v7.1-rc1: swapper_pg_dir = 0xc0603140 (offset 320) v7.1-rc1 + this fix: swapper_pg_dir = 0xc0604000 (aligned) next-20260726: swapper_pg_dir = 0xc0615140 (offset 320) next-20260726 + this fix: swapper_pg_dir = 0xc0616000 (aligned) Verified on qemu-system-microblazeel (petalogix-s3adsp1800) with mmu_defconfig and microblazeel gcc 12.5.0: v7.1-rc1 and next-20260726 both print nothing at all without the fix, and both boot to userspace with it. Link: https://lore.kernel.org/20260727215823.1422701-1-ramin.moussavi@yacoub.de Fixes:6215d9f447("arch, mm: consolidate empty_zero_page") Signed-off-by: Ramin Moussavi <ramin.moussavi@yacoub.de> Cc: Michal Simek <monstr@monstr.eu> Cc: Mike Rapoport <rppt@kernel.org> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>