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arm64/mm: Describe TTBR1_BADDR_4852_OFFSET

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TTBR1_BADDR_4852_OFFSET is a constant offset which gets added into kernel
page table physical address for TTBR1_EL1 when kernel is build for 52 bit
VA but found to be running on 48 bit VA capable system. Although there is
no explanation on how the macro is computed.

Describe TTBR1_BADDR_4852_OFFSET computation in detail via deriving from
all required parameters involved thus improving clarity and readability.

Cc: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Anshuman Khandual 2026-02-25 06:40:28 +00:00 committed by Catalin Marinas
parent 1f318b96cc
commit 2615924e45
1 changed files with 5 additions and 2 deletions
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7
arch/arm64/include/asm/pgtable-hwdef.h
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@ -287,9 +287,12 @@
#endif
#ifdef CONFIG_ARM64_VA_BITS_52
#define PTRS_PER_PGD_52_VA (UL(1) << (52 - PGDIR_SHIFT))
#define PTRS_PER_PGD_48_VA (UL(1) << (48 - PGDIR_SHIFT))
#define PTRS_PER_PGD_EXTRA (PTRS_PER_PGD_52_VA - PTRS_PER_PGD_48_VA)
/* Must be at least 64-byte aligned to prevent corruption of the TTBR */
#define TTBR1_BADDR_4852_OFFSET (((UL(1) << (52 - PGDIR_SHIFT)) - \
(UL(1) << (48 - PGDIR_SHIFT))) * 8)
#define TTBR1_BADDR_4852_OFFSET (PTRS_PER_PGD_EXTRA << PTDESC_ORDER)
#endif
#endif