Re: [PATCH 5/9] arm/mm: Get rid of READ/WRITE_SYSREG32

[Michal Orzel <michal.orzel@arm.com>]

Hi Julien,

On 20.04.2021 15:37, Julien Grall wrote:
> Hi Michal,
> 
> On 20/04/2021 08:08, Michal Orzel wrote:
>> AArch64 system registers are 64bit whereas AArch32 ones
>> are 32bit or 64bit. MSR/MRS are expecting 64bit values thus
>> we should get rid of helpers READ/WRITE_SYSREG32
>> in favour of using READ/WRITE_SYSREG.
>> We should also use register_t type when reading sysregs
>> which can correspond to uint64_t or uint32_t.
>> Even though many AArch64 sysregs have upper 32bit reserved
>> it does not mean that they can't be widen in the future.
>>
>> Modify SCTLR_EL2 accesses to use READ/WRITE_SYSREG.
> 
> SCTLR_EL2 already has bits defined in the range [32:63]. So this change is going to have a side effect as AFAICT head.S will not touch those bits. So they are now going to be preserved.
> 
> The Arm Arm defines them as unknown if implemented. Therefore shouldn't we zero them somewhere else?
> 
SCTLR_EL2 is set in head.S using SCTLR_EL2_SET which means that we are zeroing the upper 32bit half.

> In any case, I think the commit message ought to contain an analysis for system registers that happened to have bits defined in the range [32:63].
> 
>>
>> Signed-off-by: Michal Orzel <michal.orzel@arm.com>
>> ---
>>   xen/arch/arm/mm.c    | 2 +-
>>   xen/arch/arm/traps.c | 2 +-
>>   2 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
>> index 59f8a3f15f..0e07335291 100644
>> --- a/xen/arch/arm/mm.c
>> +++ b/xen/arch/arm/mm.c
>> @@ -613,7 +613,7 @@ void __init remove_early_mappings(void)
>>    */
>>   static void xen_pt_enforce_wnx(void)
>>   {
>> -    WRITE_SYSREG32(READ_SYSREG32(SCTLR_EL2) | SCTLR_Axx_ELx_WXN, SCTLR_EL2);
>> +    WRITE_SYSREG(READ_SYSREG(SCTLR_EL2) | SCTLR_Axx_ELx_WXN, SCTLR_EL2);
>>       /*
>>        * The TLBs may cache SCTLR_EL2.WXN. So ensure it is synchronized
>>        * before flushing the TLBs.
>> diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
>> index c7acdb2087..e7384381cc 100644
>> --- a/xen/arch/arm/traps.c
>> +++ b/xen/arch/arm/traps.c
>> @@ -915,7 +915,7 @@ static void _show_registers(const struct cpu_user_regs *regs,
>>       printk(" VTTBR_EL2: %016"PRIx64"\n", ctxt->vttbr_el2);
>>       printk("\n");
>>   -    printk(" SCTLR_EL2: %08"PRIx32"\n", READ_SYSREG32(SCTLR_EL2));
>> +    printk(" SCTLR_EL2: %"PRIregister"\n", READ_SYSREG(SCTLR_EL2));
>>       printk("   HCR_EL2: %"PRIregister"\n", READ_SYSREG(HCR_EL2));
>>       printk(" TTBR0_EL2: %016"PRIx64"\n", READ_SYSREG64(TTBR0_EL2));
>>       printk("\n");
>>
> 
> Cheers,
> 

Cheers,
Michal