Re: [PATCH v2] xen/arm64: Remove vreg_emulate_sysreg32

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

Hi Julien,

On 29.07.2021 13:20, Julien Grall wrote:
> Hi Michal,
> 
> On 29/07/2021 11:42, Michal Orzel wrote:
>> According to ARMv8A architecture, AArch64 registers
>> are 64bit wide even though in many cases the upper
>> 32bit is reserved. Therefore there is no need for
>> function vreg_emulate_sysreg32 on arm64. This means
>> that we can have just one function vreg_emulate_sysreg
>> using new function pointer:
>> typedef bool (*vreg_reg_fn_t)(struct cpu_user_regs *regs,
>>                                register_t *r, bool read);
>>
>> Modify vreg_emulate_cp32 to use the new function pointer
>> as well.
>>
>> This change allows to properly use 64bit registers in AArch64
>> state and in case of AArch32 the upper 32 bits of AArch64
>> registers are inaccessible and are ignored(D1.20.1 ARM DDI 0487A.j).
> 
> What you wrote only says that the bits are ignored. It doesn't say whether the bits will be 0.
> 
> They are probably, but as I wrote yesterday, I couldn't confirm it.
> 
Should I then remove this part of the commit or write below?:
"We can assume that those bits will be 0 but the architecture
reference manual does not clarify this."
>>
>> Signed-off-by: Michal Orzel <michal.orzel@arm.com>
> 
> Please provide a change log.
> 
Ok.
> Cheers,
> 
Cheers,