Re: [PATCH 2/9] arm/domain: Get rid of READ/WRITE_SYSREG32

[Julien Grall <julien@xen.org>]

On 21/04/2021 08:36, Michal Orzel wrote:
> Hi Julien,

Hi Michal,

> 
> On 20.04.2021 15:12, 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 type of registers: actlr, cntkctl to register_t.
>>
>> ACTLR is implementation defined, so in theory there might already bits already defined in the range [32:63]. So I would consider to split it from the patch so we can backport it.
>>
> You mean not to touch it at all in this series or to create a seperate patch only for ACTLR?

I meant creating a separate patch for ACTLR as part of this series.


>>> Signed-off-by: Michal Orzel <michal.orzel@arm.com>
>>> ---
>>>    xen/arch/arm/domain.c        | 20 ++++++++++----------
>>>    xen/include/asm-arm/domain.h |  4 ++--
>>>    2 files changed, 12 insertions(+), 12 deletions(-)
>>>
>>> diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
>>> index bdd3d3e5b5..c021a03c61 100644
>>> --- a/xen/arch/arm/domain.c
>>> +++ b/xen/arch/arm/domain.c
>>> @@ -113,13 +113,13 @@ static void ctxt_switch_from(struct vcpu *p)
>>>        p->arch.tpidr_el1 = READ_SYSREG(TPIDR_EL1);
>>>          /* Arch timer */
>>> -    p->arch.cntkctl = READ_SYSREG32(CNTKCTL_EL1);
>>> +    p->arch.cntkctl = READ_SYSREG(CNTKCTL_EL1);
>>>        virt_timer_save(p);
>>>          if ( is_32bit_domain(p->domain) && cpu_has_thumbee )
>>>        {
>>> -        p->arch.teecr = READ_SYSREG32(TEECR32_EL1);
>>> -        p->arch.teehbr = READ_SYSREG32(TEEHBR32_EL1);
>>> +        p->arch.teecr = READ_SYSREG(TEECR32_EL1);
>>> +        p->arch.teehbr = READ_SYSREG(TEEHBR32_EL1);
>>
>> It feels strange you converted cntkctl and actlr to use register_t but not teecr and teehbr. Can you explain why?
>>
> Because thumbee and its registers do not appear in any of ARMv8 ARM version.

This was defined on the very first version of the ARMv8-A spec (issue 
a.a) but was dropped on subsequent versinos. Hence why the compiler 
doesn't shout at you when finding TEECR32_EL1 and TEEHBR32_EL1.

> This means that this code could be protected even with #ifdef CONFIG_ARM_32 as AArch64 do not have them.

+1. The feature was completely dropped for Armv8 (even if it appeared in 
earlier version of the spec). I have checked AMD Seattle, QEMU and the 
Foundation model to confirm the feature is not exposed.

Cheers,

-- 
Julien Grall