[PATCH 4/4] arm64: mm: Defer remap of linear alias of data/bss

[Ard Biesheuvel <ardb+git@google.com>]

From: Ard Biesheuvel <ardb@kernel.org>

Marking the linear alias of data/bss invalid involves calling
set_memory_valid(), which calls split_kernel_leaf_mapping() under the
hood.

On BBML2_NOABORT capable systems, this may result in the need to
allocate page tables at a time when the generic memory allocation APIs
are not yet available, resulting in a splat like

   WARNING: arch/arm64/mm/mmu.c:821 at split_kernel_leaf_mapping+0x15c/0x170, CPU#0: swapper/0
   Modules linked in:
   CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 7.1.0-rc6 #1 PREEMPT(undef)
   pstate: a04000c9 (NzCv daIF +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
   pc : split_kernel_leaf_mapping+0x15c/0x170
   lr : update_range_prot+0x40/0x128
   sp : ffffc99ad3863c80
   ...
   Call trace:
    split_kernel_leaf_mapping+0x15c/0x170 (P)
    update_range_prot+0x40/0x128
    set_memory_valid+0x94/0xe0
    mark_linear_data_alias_valid+0x54/0x68
    map_mem+0x1fc/0x240
    paging_init+0x48/0x210
    setup_arch+0x274/0x338
    start_kernel+0x98/0x538
    __primary_switched+0x88/0x98

as reported by CKI automated testing.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/arm64/mm/mmu.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index d68e691c093a..3134f1c1097c 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1095,6 +1095,9 @@ void __init mark_linear_text_alias_ro(void)
 			    (unsigned long)__init_begin - (unsigned long)_text,
 			    PAGE_KERNEL_RO);
 
+	/* Map the kernel data/bss as invalid in the linear map */
+	mark_linear_data_alias_valid(false);
+
 	/*
 	 * Register a PM notifier to remap the linear alias of data/bss as
 	 * valid read-only before hibernation. This is needed because the
@@ -1237,9 +1240,6 @@ static void __init map_mem(void)
 		__map_memblock(start, end, pgprot_tagged(PAGE_KERNEL),
 			       flags);
 	}
-
-	/* Map the kernel data/bss as invalid in the linear map */
-	mark_linear_data_alias_valid(false);
 }
 
 void mark_rodata_ro(void)
-- 
2.54.0.1013.g208068f2d8-goog