linux-kernel - Re: [PATCH] KVM: PPC: Book3S HV: Fix guest time accounting with VIRT_CPU_ACCOUNTING

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Message-ID: <ba4aa266-ce9e-cafc-d9bb-8a6686d9e97c@redhat.com>
Date:   Fri, 2 Mar 2018 12:52:24 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Laurent Vivier <lvivier@...hat.com>, linux-kernel@...r.kernel.org
Cc:     linuxppc-dev@...ts.ozlabs.org, kvm-ppc@...r.kernel.org,
        Paul Mackerras <paulus@...abs.org>,
        David Gibson <david@...son.dropbear.id.au>
Subject: Re: [PATCH] KVM: PPC: Book3S HV: Fix guest time accounting with
 VIRT_CPU_ACCOUNTING_GEN

On 02/03/2018 11:51, Laurent Vivier wrote:
> Since commit 8b24e69fc47e ("KVM: PPC: Book3S HV: Close race with testing
> for signals on guest entry"), if CONFIG_VIRT_CPU_ACCOUNTING_GEN is set, the
> guest time is not accounted to guest time and user time, but instead to
> system time.
> 
> This is because guest_enter()/guest_exit() are called while interrupts
> are disabled and the tick counter cannot be updated between them.
> 
> To fix that, move guest_exit() after local_irq_enable(), and as
> guest_enter() is called with IRQ disabled, calls guest_enter_irqoff()
> instead.
> 
> Fixes: 8b24e69fc47e
> ("KVM: PPC: Book3S HV: Close race with testing for signals on guest entry")
> Signed-off-by: Laurent Vivier <lvivier@...hat.com>

Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>

> ---
>  arch/powerpc/kvm/book3s_hv.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 89707354c2ef..8274c2807202 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -2885,7 +2885,7 @@ static noinline void kvmppc_run_core(struct kvmppc_vcore *vc)
>  	 */
>  	trace_hardirqs_on();
>  
> -	guest_enter();
> +	guest_enter_irqoff();
>  
>  	srcu_idx = srcu_read_lock(&vc->kvm->srcu);
>  
> @@ -2893,8 +2893,6 @@ static noinline void kvmppc_run_core(struct kvmppc_vcore *vc)
>  
>  	srcu_read_unlock(&vc->kvm->srcu, srcu_idx);
>  
> -	guest_exit();
> -
>  	trace_hardirqs_off();
>  	set_irq_happened(trap);
>  
> @@ -2937,6 +2935,7 @@ static noinline void kvmppc_run_core(struct kvmppc_vcore *vc)
>  	kvmppc_set_host_core(pcpu);
>  
>  	local_irq_enable();
> +	guest_exit();
>  
>  	/* Let secondaries go back to the offline loop */
>  	for (i = 0; i < controlled_threads; ++i) {
>