Re: [Qemu-devel] [PATCH] target/arm: fix CBAR register for AArch64 CPUs

[Luc Michel]

Hi Peter,

On 9/12/19 6:03 PM, Peter Maydell wrote:
> On Thu, 12 Sep 2019 at 12:01, Luc Michel <address@hidden> wrote:
>>
>> For AArch64 CPUs with a CBAR register, we have two views for it:
>>   - in AArch64 state, the CBAR_EL1 register (S3_1_C15_C3_0), returns the
>>     full 64 bits CBAR value
>>   - in AArch32 state, the CBAR register (cp15, opc1=1, CRn=15, CRm=3, opc2=0)
>>     returns a 32 bits view such that:
>>       CBAR = CBAR_EL1[31:18] 0..0 CBAR_EL1[43:32]
>>
>> This commit fixes the current implementation where:
>>   - CBAR_EL1 was returning the 32 bits view instead of the full 64 bits
>>     value,
>>   - CBAR was returning a truncated 32 bits version of the full 64 bits
>>     one, instead of the 32 bits view
>>   - CBAR was declared as cp15, opc1=4, CRn=15, CRm=0, opc2=0, which is
>>     the CBAR register found in the ARMv7 Cortex-Ax CPUs, but not in
>>     ARMv8 CPUs.
>>
>> Signed-off-by: Luc Michel <address@hidden>
>> ---
>>  target/arm/helper.c | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/target/arm/helper.c b/target/arm/helper.c
>> index 507026c915..755aa18a2d 100644
>> --- a/target/arm/helper.c
>> +++ b/target/arm/helper.c
>> @@ -6740,12 +6740,12 @@ void register_cp_regs_for_features(ARMCPU *cpu)
>>              ARMCPRegInfo cbar_reginfo[] = {
>>                  { .name = "CBAR",
>>                    .type = ARM_CP_CONST,
>> -                  .cp = 15, .crn = 15, .crm = 0, .opc1 = 4, .opc2 = 0,
>> -                  .access = PL1_R, .resetvalue = cpu->reset_cbar },
>> +                  .cp = 15, .crn = 15, .crm = 3, .opc1 = 1, .opc2 = 0,
>> +                  .access = PL1_R, .resetvalue = cbar32 },
> 
> This will break the Cortex-A9 &c which use the 15/0/4/0 encoding
> and the un-rearranged value for this register.
I don't think so because we are in the "if (arm_feature(env,
ARM_FEATURE_AARCH64))" branch of the code. The else branch still maps
15/0/4/0 for non-AArch64 CPUs.

> 
> I think we need to check through the TRMs to confirm which CPUs use
> which format for the CBAR, and have a different feature bit for the
> newer format/sysreg encoding, so we can provide the right sysregs for
> the right cores.
I checked all the AArch64 Cortex's TRMs, for those having a PERIPHBASE
signal and CBAR register (namely Cortex-A53, 57, 72, 73), they all match
the mapping I put in this patch, so I think we don't need to split the
CBAR feature further. I believe more recent Cortex's address the GIC
using coprocessor registers, and CBAR does not exist in those ones.

-- 
Luc

> 
> thanks
> -- PMM
>