On Thu, Feb 05, 2015 at 03:23:51PM -0500, riel@xxxxxxxxxx wrote:
> From: Rik van Riel <riel@xxxxxxxxxx>
>
> The host kernel is not doing anything while the CPU is executing
> a KVM guest VCPU, so it can be marked as being in an extended
> quiescent state, identical to that used when running user space
> code.
>
> The only exception to that rule is when the host handles an
> interrupt, which is already handled by the irq code, which
> calls rcu_irq_enter and rcu_irq_exit.
>
> The guest_enter and guest_exit functions already switch vtime
> accounting independent of context tracking, so leave those calls
> where they are, instead of moving them into the context tracking
> code.
>
> Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>
> ---
> include/linux/context_tracking.h | 8 +++++++-
> include/linux/context_tracking_state.h | 1 +
> include/linux/kvm_host.h | 3 ++-
> 3 files changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
> index bd9f000fc98d..a5d3bb44b897 100644
> --- a/include/linux/context_tracking.h
> +++ b/include/linux/context_tracking.h
> @@ -43,7 +43,7 @@ static inline enum ctx_state exception_enter(void)
> static inline void exception_exit(enum ctx_state prev_ctx)
> {
> if (context_tracking_is_enabled()) {
> - if (prev_ctx == IN_USER)
> + if (prev_ctx == IN_USER || prev_ctx == IN_GUEST)
That's nitpicking but != IN_KERNEL would be more generic. We are exiting an exception
and we know that the exception executes IN_KERNEL, so we want to restore any context
(whether IN_USER, IN_GUEST, or anything added in the future) prior the exception if that
was anything else than IN_KERNEL.
> context_tracking_user_enter(prev_ctx);
> }
> }
> @@ -78,6 +78,9 @@ static inline void guest_enter(void)
> vtime_guest_enter(current);
> else
> current->flags |= PF_VCPU;
> +
> + if (context_tracking_is_enabled())
> + context_tracking_user_enter(IN_GUEST);
> }
>
> static inline void guest_exit(void)
> @@ -86,6 +89,9 @@ static inline void guest_exit(void)
> vtime_guest_exit(current);
> else
> current->flags &= ~PF_VCPU;
> +
> + if (context_tracking_is_enabled())
> + context_tracking_user_exit(IN_GUEST);
I suggest you to restore RCU before anything else. I believe cputime
accounting doesn't use RCU but we never know with all the debug/tracing
code behind, the acct accounting...
Thanks.
> }
>
> #else
> diff --git a/include/linux/context_tracking_state.h b/include/linux/context_tracking_state.h
> index 97a81225d037..f3ef027af749 100644
> --- a/include/linux/context_tracking_state.h
> +++ b/include/linux/context_tracking_state.h
> @@ -15,6 +15,7 @@ struct context_tracking {
> enum ctx_state {
> IN_KERNEL = 0,
> IN_USER,
> + IN_GUEST,
> } state;
> };
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 26f106022c88..c7828a6a9614 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -772,7 +772,8 @@ static inline void kvm_guest_enter(void)
> * one time slice). Lets treat guest mode as quiescent state, just like
> * we do with user-mode execution.
> */
> - rcu_virt_note_context_switch(smp_processor_id());
> + if (!context_tracking_cpu_is_enabled())
> + rcu_virt_note_context_switch(smp_processor_id());
> }
>
> static inline void kvm_guest_exit(void)
> --
> 1.9.3
>
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