[PATCH v3 14/17] KVM: arm64: Macros for setting/clearing FGT bits

[Marc Zyngier]

On Thu, 14 Dec 2023 10:01:54 +0000,
Fuad Tabba <tabba at google.com> wrote:
> 
> There's a lot of boilerplate code for setting and clearing FGT
> bits when activating guest traps. Refactor it into macros. These
> macros will also be used in future patch series.
> 
> No functional change intended.
> 
> Signed-off-by: Fuad Tabba <tabba at google.com>
> ---
>  arch/arm64/kvm/hyp/include/hyp/switch.h | 60 +++++++++----------------
>  1 file changed, 21 insertions(+), 39 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h
> index 17ce40f5b006..e223fc0d5193 100644
> --- a/arch/arm64/kvm/hyp/include/hyp/switch.h
> +++ b/arch/arm64/kvm/hyp/include/hyp/switch.h
> @@ -79,6 +79,23 @@ static inline void __activate_traps_fpsimd32(struct kvm_vcpu *vcpu)
>  		clr |= ~hfg & __ ## reg ## _nMASK; 			\
>  	} while(0)
>  
> +#define update_fgt_traps_cs(reg, clr, set)				\
> +	do {								\
> +		struct kvm_cpu_context *hctxt =				\
> +			&this_cpu_ptr(&kvm_host_data)->host_ctxt;	\
> +		u64 val, c = 0, s = 0;					\
> +									\
> +		ctxt_sys_reg(hctxt, reg) = read_sysreg_s(SYS_ ## reg);	\
> +		compute_clr_set(vcpu, reg, c, s);			\

You are referring to a variable name that is in the scope of the macro
user, and not the macro itself. It is so fragile it isn't funny.

Why don't you simply pass the vcpu as a parameter to the function?

Another thing is that this read/write can be expensive. How about not
doing anything when there is no change to the value of the sysreg?

I'll see if I can come up with something.

	M.

-- 
Without deviation from the norm, progress is not possible.