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Why NEON instructions can't be executed in NSEL1 when HCR_EL2.ID and HCR_EL2_CD are set?

tiger20081015

Hi,  I have a test application on A55 which starts in EL3 mode, then switches to NSEL1 to execute some neon instructions.  I noticed that the value of HCR_EL2.ID (bit 33) and HCR_EL2.CD (bit 32) will affect the behavior of neon instruction execution, which are:

  1. if both bits are 1, the core falls to exception when neon instructions are executed in NSEL1.  However, in EL3, neon instructions works well.

            The NEON instruction is：“str q0 [ x1，#0x60]”

            Exception message: SPSR 0x3c9, ELR 0x400, ESR 0x82000010

            If replace the NEON instruction to normal instruction “str  x0  [x1, #60]”, it works well.

        2. if both bits are 0, neon instructions works well in both NSEL1 and EL3.

On the technical manual, the ID bit and CD bit only affects the behavior of instruction cache and data cache in NSEL0 and NSEL1, and they should not related to neon operations.

Is there any clue that why HCR_EL2 value affects the neon instructions?

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