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| author | Steve Capper <steve.capper@arm.com> | 2018-12-06 23:50:39 +0100 |
|---|---|---|
| committer | Will Deacon <will.deacon@arm.com> | 2018-12-10 19:42:17 +0100 |
| commit | e842dfb5a2d3b4c43766508ef89a4eb67471d53a (patch) | |
| tree | bd1f000f150d08364cf7b306c26ded21f0676f1a /arch/arm64/kernel/hibernate-asm.S | |
| parent | arm64: mm: Define arch_get_mmap_end, arch_get_mmap_base (diff) | |
| download | linux-e842dfb5a2d3b4c43766508ef89a4eb67471d53a.tar.xz linux-e842dfb5a2d3b4c43766508ef89a4eb67471d53a.zip | |
arm64: mm: Offset TTBR1 to allow 52-bit PTRS_PER_PGD
Enabling 52-bit VAs on arm64 requires that the PGD table expands from 64
entries (for the 48-bit case) to 1024 entries. This quantity,
PTRS_PER_PGD is used as follows to compute which PGD entry corresponds
to a given virtual address, addr:
pgd_index(addr) -> (addr >> PGDIR_SHIFT) & (PTRS_PER_PGD - 1)
Userspace addresses are prefixed by 0's, so for a 48-bit userspace
address, uva, the following is true:
(uva >> PGDIR_SHIFT) & (1024 - 1) == (uva >> PGDIR_SHIFT) & (64 - 1)
In other words, a 48-bit userspace address will have the same pgd_index
when using PTRS_PER_PGD = 64 and 1024.
Kernel addresses are prefixed by 1's so, given a 48-bit kernel address,
kva, we have the following inequality:
(kva >> PGDIR_SHIFT) & (1024 - 1) != (kva >> PGDIR_SHIFT) & (64 - 1)
In other words a 48-bit kernel virtual address will have a different
pgd_index when using PTRS_PER_PGD = 64 and 1024.
If, however, we note that:
kva = 0xFFFF << 48 + lower (where lower[63:48] == 0b)
and, PGDIR_SHIFT = 42 (as we are dealing with 64KB PAGE_SIZE)
We can consider:
(kva >> PGDIR_SHIFT) & (1024 - 1) - (kva >> PGDIR_SHIFT) & (64 - 1)
= (0xFFFF << 6) & 0x3FF - (0xFFFF << 6) & 0x3F // "lower" cancels out
= 0x3C0
In other words, one can switch PTRS_PER_PGD to the 52-bit value globally
provided that they increment ttbr1_el1 by 0x3C0 * 8 = 0x1E00 bytes when
running with 48-bit kernel VAs (TCR_EL1.T1SZ = 16).
For kernel configuration where 52-bit userspace VAs are possible, this
patch offsets ttbr1_el1 and sets PTRS_PER_PGD corresponding to the
52-bit value.
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Steve Capper <steve.capper@arm.com>
[will: added comment to TTBR1_BADDR_4852_OFFSET calculation]
Signed-off-by: Will Deacon <will.deacon@arm.com>
Diffstat (limited to 'arch/arm64/kernel/hibernate-asm.S')
| -rw-r--r-- | arch/arm64/kernel/hibernate-asm.S | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/arch/arm64/kernel/hibernate-asm.S b/arch/arm64/kernel/hibernate-asm.S index dd14ab8c9f72..fe36d85c60bd 100644 --- a/arch/arm64/kernel/hibernate-asm.S +++ b/arch/arm64/kernel/hibernate-asm.S @@ -40,6 +40,7 @@ tlbi vmalle1 dsb nsh phys_to_ttbr \tmp, \page_table + offset_ttbr1 \tmp msr ttbr1_el1, \tmp isb .endm |