Re: [PATCH 1/4] KVM: PPC: Book3s: PR: Disable preemption in vcpu_run

[Scott Wood <scottwood@freescale.com>]

On 12/09/2011 09:26 AM, Alexander Graf wrote:
> When entering the guest, we want to make sure we're not getting preempted
> away, so let's disable preemption on entry, but enable it again while handling
> guest exits.
> 
> Reported-by: Jörg Sommer <joerg@alea.gnuu.de>
> Signed-off-by: Alexander Graf <agraf@suse.de>
> ---
>  arch/powerpc/kvm/book3s_pr.c |    7 +++++++
>  1 files changed, 7 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/powerpc/kvm/book3s_pr.c b/arch/powerpc/kvm/book3s_pr.c
> index 726512b..8e4f800 100644
> --- a/arch/powerpc/kvm/book3s_pr.c
> +++ b/arch/powerpc/kvm/book3s_pr.c
> @@ -519,6 +519,7 @@ int kvmppc_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu,
>  	run->ready_for_interrupt_injection = 1;
>  
>  	trace_kvm_book3s_exit(exit_nr, vcpu);
> +	preempt_enable();
>  	kvm_resched(vcpu);
>  	switch (exit_nr) {
>  	case BOOK3S_INTERRUPT_INST_STORAGE:
> @@ -763,6 +764,8 @@ program_interrupt:
>  			run->exit_reason = KVM_EXIT_INTR;
>  			r = -EINTR;
>  		} else {
> +			preempt_disable();
> +
>  			/* In case an interrupt came in that was triggered
>  			 * from userspace (like DEC), we need to check what
>  			 * to inject now! */

Shouldn't you really have interrupts disabled here, as booke does?

Otherwise an interrupt (including an IPI kick) could send you a signal
or guest exception after you check.

Likewise for other guest entry points.

-Scott