2018-03-02 10:54:23

by Laurent Vivier

Subject: [PATCH] KVM: PPC: Book3S HV: Fix guest time accounting with VIRT_CPU_ACCOUNTING_GEN

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 <[email protected]>
---
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) {
--
2.14.3

2018-03-02 11:53:32

by Paolo Bonzini

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 <[email protected]>

Reviewed-by: Paolo Bonzini <[email protected]>

> ---
> 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) {
>

2018-03-04 23:02:37

by Paul Mackerras

Subject: Re: [PATCH] KVM: PPC: Book3S HV: Fix guest time accounting with VIRT_CPU_ACCOUNTING_GEN

On Fri, Mar 02, 2018 at 11:51:56AM +0100, 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 <[email protected]>

Thanks, applied to my kvm-ppc-fixes branch.

Paul.