[PATCH V2 12/14] arm64/mm: Relax KASAN shadow alignment for FEAT_D128

[Anshuman Khandual]

D128 reduces the number of descriptors in each translation table, causing
some VA size and page granule combinations that use two page table levels
with D64 to now require three levels.

For three-level page tables, the PUD level is folded while the PMD level
remains a real translation level. Hence, PUD_SIZE represents a root-level
span. With D128, some configurations have a KASAN shadow region smaller
than this span, making it impossible for both KASAN shadow boundaries to
satisfy the existing PUD_SIZE alignment requirement.

The KASAN initialization code on arm64 already supports shadow boundaries
which are not root-level aligned, by installing or cloning the next-level
table as required.

Similarly for three level D128 page tables, relax SHADOW_ALIGN to PMD_SIZE,
which corresponds to the first non-folded level below the root level. Keep
the existing alignment requirements unchanged for all other configurations.

Cc: Andrey Ryabinin <ryabinin.a.a at gmail.com>
Cc: Alexander Potapenko <glider at google.com>
Cc: Andrey Konovalov <andreyknvl at gmail.com>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Will Deacon <will at kernel.org>
Cc: Mark Rutland <mark.rutland at arm.com>
Cc: kasan-dev at googlegroups.com
Cc: linux-arm-kernel at lists.infradead.org
Cc: linux-kernel at vger.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual at arm.com>
---
 arch/arm64/mm/kasan_init.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
index f61f5bc09467..e12abea6ad15 100644
--- a/arch/arm64/mm/kasan_init.c
+++ b/arch/arm64/mm/kasan_init.c
@@ -178,7 +178,9 @@ static void __init kasan_pgd_populate(unsigned long addr, unsigned long end,
 	} while (pgdp++, addr = next, addr != end);
 }
 
-#if defined(CONFIG_ARM64_64K_PAGES) || CONFIG_PGTABLE_LEVELS > 4
+#if defined(CONFIG_ARM64_D128) && CONFIG_PGTABLE_LEVELS == 3
+#define SHADOW_ALIGN	PMD_SIZE
+#elif defined(CONFIG_ARM64_64K_PAGES) || CONFIG_PGTABLE_LEVELS > 4
 #define SHADOW_ALIGN	P4D_SIZE
 #else
 #define SHADOW_ALIGN	PUD_SIZE
-- 
2.43.0