On 12/12/2013 10:23 AM, Peter Maydell wrote:
> On 12 December 2013 02:28, Christoffer Dall <christoffer.dall@xxxxxxxxxx> wrote:
>> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
>> index a30035d..9565e6a 100644
>> --- a/Documentation/virtual/kvm/api.txt
>> +++ b/Documentation/virtual/kvm/api.txt
>> @@ -1889,9 +1889,12 @@ value in the kvm_regs structure seen as a 32bit array.
>> arm64 CCSIDR registers are demultiplexed by CSSELR value:
>> 0x6020 0000 0011 00 <csselr:8>
>>
>> -arm64 system registers have the following id bit patterns:
>> +arm64 64-bit system registers have the following id bit patterns:
>> 0x6030 0000 0013 <op0:2> <op1:3> <crn:4> <crm:4> <op2:3>
>>
>> +arm64 32-bit system registers have the following id bit patterns:
>> + 0x6020 0000 0013 <op0:2> <op1:3> <crn:4> <crm:4> <op2:3>
>
> What does it mean to say that a system register for AArch64
> is "32 bits" given that MRS/MSR always operate on a 64 bit
> register? We have the distinction in AArch32 because the
> instructions (and whether the input/output is in one register
> or a register pair) are different, but I can't see the need for
> AArch64.
But ARMv8 ARM still defines these registers as 32-bit:
D8.5.14: CNTV_CTL_EL0
Attributes
CNTV_CTL_EL0 is a 32-bit register.
But indeed the MSR/MRS instruction references a Xt register, and the
documentation does not seem to tell how this is handled, so I assume
this is zero-extended.
Would be great to have this clarified, though.
Regards,
Andre.
>
> (The code I've just written for QEMU to handle sysregs says
> "they're all 64 bit"...)
>
> thanks
> -- PMM
>
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