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    arm64: Work around Falkor erratum 1003 · 38fd94b0
    Christopher Covington authored
    
    
    The Qualcomm Datacenter Technologies Falkor v1 CPU may allocate TLB entries
    using an incorrect ASID when TTBRx_EL1 is being updated. When the erratum
    is triggered, page table entries using the new translation table base
    address (BADDR) will be allocated into the TLB using the old ASID. All
    circumstances leading to the incorrect ASID being cached in the TLB arise
    when software writes TTBRx_EL1[ASID] and TTBRx_EL1[BADDR], a memory
    operation is in the process of performing a translation using the specific
    TTBRx_EL1 being written, and the memory operation uses a translation table
    descriptor designated as non-global. EL2 and EL3 code changing the EL1&0
    ASID is not subject to this erratum because hardware is prohibited from
    performing translations from an out-of-context translation regime.
    
    Consider the following pseudo code.
    
      write new BADDR and ASID values to TTBRx_EL1
    
    Replacing the above sequence with the one below will ensure that no TLB
    entries with an incorrect ASID are used by software.
    
      write reserved value to TTBRx_EL1[ASID]
      ISB
      write new value to TTBRx_EL1[BADDR]
      ISB
      write new value to TTBRx_EL1[ASID]
      ISB
    
    When the above sequence is used, page table entries using the new BADDR
    value may still be incorrectly allocated into the TLB using the reserved
    ASID. Yet this will not reduce functionality, since TLB entries incorrectly
    tagged with the reserved ASID will never be hit by a later instruction.
    
    Based on work by Shanker Donthineni <shankerd@codeaurora.org>
    
    Reviewed-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
    Signed-off-by: default avatarChristopher Covington <cov@codeaurora.org>
    Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
    38fd94b0