On Fri, Sep 21, 2018 at 08:01:38PM +1000, Paul Mackerras wrote:
> Currently kvmppc_handle_exit_hv() is called with the vcore lock held
> because it is called within a for_each_runnable_thread loop.
> However, we already unlock the vcore within kvmppc_handle_exit_hv()
> under certain circumstances, and this is safe because (a) any vcpus
> that become runnable and are added to the runnable set by
> kvmppc_run_vcpu() have their vcpu->arch.trap == 0 and can't actually
> run in the guest (because the vcore state is VCORE_EXITING), and
> (b) for_each_runnable_thread is safe against addition or removal
> of vcpus from the runnable set.
>
> Therefore, in order to simplify things for following patches, let's
> drop the vcore lock in the for_each_runnable_thread loop, so
> kvmppc_handle_exit_hv() gets called without the vcore lock held.
>
> Signed-off-by: Paul Mackerras <paulus@xxxxxxxxxx>
Reviewed-by: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx>
> ---
> arch/powerpc/kvm/book3s_hv.c | 19 ++++++++++---------
> 1 file changed, 10 insertions(+), 9 deletions(-)
>
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 49a686c..0e17593 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -1084,7 +1084,6 @@ static int kvmppc_emulate_doorbell_instr(struct kvm_vcpu *vcpu)
> return RESUME_GUEST;
> }
>
> -/* Called with vcpu->arch.vcore->lock held */
> static int kvmppc_handle_exit_hv(struct kvm_run *run, struct kvm_vcpu *vcpu,
> struct task_struct *tsk)
> {
> @@ -1205,10 +1204,7 @@ static int kvmppc_handle_exit_hv(struct kvm_run *run, struct kvm_vcpu *vcpu,
> swab32(vcpu->arch.emul_inst) :
> vcpu->arch.emul_inst;
> if (vcpu->guest_debug & KVM_GUESTDBG_USE_SW_BP) {
> - /* Need vcore unlocked to call kvmppc_get_last_inst */
> - spin_unlock(&vcpu->arch.vcore->lock);
> r = kvmppc_emulate_debug_inst(run, vcpu);
> - spin_lock(&vcpu->arch.vcore->lock);
> } else {
> kvmppc_core_queue_program(vcpu, SRR1_PROGILL);
> r = RESUME_GUEST;
> @@ -1224,12 +1220,8 @@ static int kvmppc_handle_exit_hv(struct kvm_run *run, struct kvm_vcpu *vcpu,
> case BOOK3S_INTERRUPT_H_FAC_UNAVAIL:
> r = EMULATE_FAIL;
> if (((vcpu->arch.hfscr >> 56) == FSCR_MSGP_LG) &&
> - cpu_has_feature(CPU_FTR_ARCH_300)) {
> - /* Need vcore unlocked to call kvmppc_get_last_inst */
> - spin_unlock(&vcpu->arch.vcore->lock);
> + cpu_has_feature(CPU_FTR_ARCH_300))
> r = kvmppc_emulate_doorbell_instr(vcpu);
> - spin_lock(&vcpu->arch.vcore->lock);
> - }
> if (r == EMULATE_FAIL) {
> kvmppc_core_queue_program(vcpu, SRR1_PROGILL);
> r = RESUME_GUEST;
> @@ -2599,6 +2591,14 @@ static void post_guest_process(struct kvmppc_vcore *vc, bool is_master)
> spin_lock(&vc->lock);
> now = get_tb();
> for_each_runnable_thread(i, vcpu, vc) {
> + /*
> + * It's safe to unlock the vcore in the loop here, because
> + * for_each_runnable_thread() is safe against removal of
> + * the vcpu, and the vcore state is VCORE_EXITING here,
> + * so any vcpus becoming runnable will have their arch.trap
> + * set to zero and can't actually run in the guest.
> + */
> + spin_unlock(&vc->lock);
> /* cancel pending dec exception if dec is positive */
> if (now < vcpu->arch.dec_expires &&
> kvmppc_core_pending_dec(vcpu))
> @@ -2614,6 +2614,7 @@ static void post_guest_process(struct kvmppc_vcore *vc, bool is_master)
> vcpu->arch.ret = ret;
> vcpu->arch.trap = 0;
>
> + spin_lock(&vc->lock);
> if (is_kvmppc_resume_guest(vcpu->arch.ret)) {
> if (vcpu->arch.pending_exceptions)
> kvmppc_core_prepare_to_enter(vcpu);
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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