• Steve Capper's avatar
    arm64: mm: introduce 52-bit userspace support · 67e7fdfc
    Steve Capper authored
    On arm64 there is optional support for a 52-bit virtual address space.
    To exploit this one has to be running with a 64KB page size and be
    running on hardware that supports this.
    
    For an arm64 kernel supporting a 48 bit VA with a 64KB page size,
    some changes are needed to support a 52-bit userspace:
     * TCR_EL1.T0SZ needs to be 12 instead of 16,
     * TASK_SIZE needs to reflect the new size.
    
    This patch implements the above when the support for 52-bit VAs is
    detected at early boot time.
    
    On arm64 userspace addresses translation is controlled by TTBR0_EL1. As
    well as userspace, TTBR0_EL1 controls:
     * The identity mapping,
     * EFI runtime code.
    
    It is possible to run a kernel with an identity mapping that has a
    larger VA size than userspace (and for this case __cpu_set_tcr_t0sz()
    would set TCR_EL1.T0SZ as appropriate). However, when the conditions for
    52-bit userspace are met; it is possible to keep TCR_EL1.T0SZ fixed at
    12. Thus in this patch, the TCR_EL1.T0SZ size changing logic is
    disabled.
    Reviewed-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
    Signed-off-by: default avatarSteve Capper <steve.capper@arm.com>
    Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
    67e7fdfc
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