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

[Julien Grall <julien@xxxxxxx>]

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.

> Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
Please provide a change log.

Cheers,

--
Julien Grall