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DC GZVA, Data Cache set Allocation Tags and Zero by VA

The DC GZVA characteristics are:

Purpose

Zero data and write a value to the Allocation Tags of a naturally aligned block of N bytes, where the size of N is identified in DCZID_EL0. The Allocation Tag used is determined by the input address.

Configuration

This instruction is present only when ARMv8.5-MemTag is implemented. Otherwise, direct accesses to DC GZVA are UNDEFINED.

Attributes

DC GZVA is a 64-bit System instruction.

Field descriptions

The DC GZVA input value bit assignments are:

6362616059585756555453525150494847464544434241403938373635343332
Virtual address to use
Virtual address to use
313029282726252423222120191817161514131211109876543210

Bits [63:0]

Virtual address to use. There is no alignment restriction on the address within the block of N bytes that is used.

Executing the DC GZVA instruction

When this instruction is executed, it can generate memory faults or watchpoints which are prioritized in the same way as other memory-related faults or watchpoints. If a synchronous data abort fault or a watchpoint is generated, the CM bit in the ESR_ELx.ISS field is not set.

If the memory region being zeroed is any type of Device memory, this instruction can give an alignment fault which is prioritized in the same way as other alignment faults that are determined by the memory type.

This instruction applies to Normal memory regardless of cacheability attributes.

This instruction behaves as a set of Stores to each byte within the block being accessed, and so it:

  • Generates a Permission Fault if the translation system does not permit writes to the locations.
  • Requires the same considerations for ordering and the management of coherency as any other store instructions.

Accesses to this instruction use the following encodings:

DC GZVA, <Xt>

op0op1CRnCRmop2
0b010b0110b01110b01000b100
if PSTATE.EL == EL0 then
    if !ELUsingAArch32(EL1) && !(EL2Enabled() && HCR_EL2.<E2H,TGE> == '11') && SCTLR_EL1.DZE == '0' then
        if EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.TGE == '1' then
            AArch64.SystemAccessTrap(EL2, 0x18);
        else
            AArch64.SystemAccessTrap(EL1, 0x18);
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.<E2H,TGE> != '11' && HCR_EL2.TDZ == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.<E2H,TGE> == '11' && SCTLR_EL2.DZE == '0' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    else
        DC_GZVA(X[t]);
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.TDZ == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    else
        DC_GZVA(X[t]);
elsif PSTATE.EL == EL2 then
    DC_GZVA(X[t]);
elsif PSTATE.EL == EL3 then
    DC_GZVA(X[t]);
              


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