Re: [PATCH 15/27] Add mfdec emulation

From: Hollis Blanchard <hollisb@us.ibm.com>
To: kvm-ppc@vger.kernel.org
Subject: Re: [PATCH 15/27] Add mfdec emulation
Date: Fri, 09 Oct 2009 20:45:34 +0000	[thread overview]
Message-ID: <1255121134.2546.139.camel@slab.beaverton.ibm.com> (raw)
In-Reply-To: <1254212303-8737-16-git-send-email-agraf@suse.de>

On Tue, 2009-09-29 at 10:18 +0200, Alexander Graf wrote:
> We support setting the DEC to a certain value right now. Doing that basically
> triggers the CPU local timer.
> 
> But there's also an mfdec command that enabled the OS to read the decrementor.
> 
> This is required at least by all desktop and server PowerPC Linux kernels. It
> can't really hurt to allow embedded ones to do it as well though.
> 
> Signed-off-by: Alexander Graf <agraf@suse.de>
> ---
>  arch/powerpc/kvm/emulate.c |   13 ++++++++++++-
>  1 files changed, 12 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/powerpc/kvm/emulate.c b/arch/powerpc/kvm/emulate.c
> index 7737146..50d411d 100644
> --- a/arch/powerpc/kvm/emulate.c
> +++ b/arch/powerpc/kvm/emulate.c
> @@ -66,12 +66,14 @@
> 
>  void kvmppc_emulate_dec(struct kvm_vcpu *vcpu)
>  {
> +	unsigned long nr_jiffies;
> +
>  	if (vcpu->arch.tcr & TCR_DIE) {
>  		/* The decrementer ticks at the same rate as the timebase, so
>  		 * that's how we convert the guest DEC value to the number of
>  		 * host ticks. */
> -		unsigned long nr_jiffies;
> 
> +		vcpu->arch.dec_jiffies = mftb();
>  		nr_jiffies = vcpu->arch.dec / tb_ticks_per_jiffy;
>  		mod_timer(&vcpu->arch.dec_timer,
>  		          get_jiffies_64() + nr_jiffies);
> @@ -211,6 +213,15 @@ int kvmppc_emulate_instruction(struct kvm_run *run, struct kvm_vcpu *vcpu)
>  			/* Note: SPRG4-7 are user-readable, so we don't get
>  			 * a trap. */
> 
> +			case SPRN_DEC:
> +			{
> +				u64 jd = mftb() - vcpu->arch.dec_jiffies;
> +				vcpu->arch.gpr[rt] = vcpu->arch.dec - jd;
> +#ifdef DEBUG_EMUL
> +				printk(KERN_INFO "mfDEC: %x - %llx = %lx\n", vcpu->arch.dec, jd, vcpu->arch.gpr[rt]);
> +#endif
> +				break;
> +			}
>  			default:
>  				emulated = kvmppc_core_emulate_mfspr(vcpu, sprn, rt);
>  				if (emulated = EMULATE_FAIL) {

mftb() doesn't exist for ppc32, so we'll need to use the get_tb()
wrapper instead.

-- 
Hollis Blanchard
IBM Linux Technology Center