Re: [PATCH 11/21] MIPS: KVM: Rewrite count/compare timer emulation

[David Daney <ddaney.cavm@gmail.com>]

[...]
> diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h
> index f56bb699506e..57c1085fd6ab 100644
> --- a/arch/mips/include/asm/kvm_host.h
> +++ b/arch/mips/include/asm/kvm_host.h
> @@ -404,8 +404,15 @@ struct kvm_vcpu_arch {
>
>   	u32 io_gpr;		/* GPR used as IO source/target */
>
> -	/* Used to calibrate the virutal count register for the guest */
> -	int32_t host_cp0_count;
> +	struct hrtimer comparecount_timer;
> +	/* Count bias from the raw time */
> +	uint32_t count_bias;
> +	/* Frequency of timer in Hz */
> +	uint32_t count_hz;

We are currently running with timer frequencies of over 2GHz, so the 
width of this variable is close to the limit.

Your follow-on patch exports this to user-space as part of the KVM ABI.

I would suggest, at least for the user-space ABI, to make this a 64-bit 
wide value.


> +	/* Dynamic nanosecond bias (multiple of count_period) to avoid overflow */
> +	s64 count_dyn_bias;
> +	/* Period of timer tick in ns */
> +	u64 count_period;
>
>   	/* Bitmask of exceptions that are pending */
[...]