diff options
Diffstat (limited to 'arch/powerpc/include/asm/kvm_ppc.h')
| -rw-r--r-- | arch/powerpc/include/asm/kvm_ppc.h | 100 |
1 files changed, 97 insertions, 3 deletions
diff --git a/arch/powerpc/include/asm/kvm_ppc.h b/arch/powerpc/include/asm/kvm_ppc.h index 8e8514efb124..ee62776e5433 100644 --- a/arch/powerpc/include/asm/kvm_ppc.h +++ b/arch/powerpc/include/asm/kvm_ppc.h @@ -452,9 +452,100 @@ static inline u32 kvmppc_get_xics_latch(void) return xirr; } -static inline void kvmppc_set_host_ipi(int cpu, u8 host_ipi) +/* + * To avoid the need to unnecessarily exit fully to the host kernel, an IPI to + * a CPU thread that's running/napping inside of a guest is by default regarded + * as a request to wake the CPU (if needed) and continue execution within the + * guest, potentially to process new state like externally-generated + * interrupts or IPIs sent from within the guest itself (e.g. H_PROD/H_IPI). + * + * To force an exit to the host kernel, kvmppc_set_host_ipi() must be called + * prior to issuing the IPI to set the corresponding 'host_ipi' flag in the + * target CPU's PACA. To avoid unnecessary exits to the host, this flag should + * be immediately cleared via kvmppc_clear_host_ipi() by the IPI handler on + * the receiving side prior to processing the IPI work. + * + * NOTE: + * + * We currently issue an smp_mb() at the beginning of kvmppc_set_host_ipi(). + * This is to guard against sequences such as the following: + * + * CPU + * X: smp_muxed_ipi_set_message(): + * X: smp_mb() + * X: message[RESCHEDULE] = 1 + * X: doorbell_global_ipi(42): + * X: kvmppc_set_host_ipi(42) + * X: ppc_msgsnd_sync()/smp_mb() + * X: ppc_msgsnd() -> 42 + * 42: doorbell_exception(): // from CPU X + * 42: ppc_msgsync() + * 105: smp_muxed_ipi_set_message(): + * 105: smb_mb() + * // STORE DEFERRED DUE TO RE-ORDERING + * --105: message[CALL_FUNCTION] = 1 + * | 105: doorbell_global_ipi(42): + * | 105: kvmppc_set_host_ipi(42) + * | 42: kvmppc_clear_host_ipi(42) + * | 42: smp_ipi_demux_relaxed() + * | 42: // returns to executing guest + * | // RE-ORDERED STORE COMPLETES + * ->105: message[CALL_FUNCTION] = 1 + * 105: ppc_msgsnd_sync()/smp_mb() + * 105: ppc_msgsnd() -> 42 + * 42: local_paca->kvm_hstate.host_ipi == 0 // IPI ignored + * 105: // hangs waiting on 42 to process messages/call_single_queue + * + * We also issue an smp_mb() at the end of kvmppc_clear_host_ipi(). This is + * to guard against sequences such as the following (as well as to create + * a read-side pairing with the barrier in kvmppc_set_host_ipi()): + * + * CPU + * X: smp_muxed_ipi_set_message(): + * X: smp_mb() + * X: message[RESCHEDULE] = 1 + * X: doorbell_global_ipi(42): + * X: kvmppc_set_host_ipi(42) + * X: ppc_msgsnd_sync()/smp_mb() + * X: ppc_msgsnd() -> 42 + * 42: doorbell_exception(): // from CPU X + * 42: ppc_msgsync() + * // STORE DEFERRED DUE TO RE-ORDERING + * -- 42: kvmppc_clear_host_ipi(42) + * | 42: smp_ipi_demux_relaxed() + * | 105: smp_muxed_ipi_set_message(): + * | 105: smb_mb() + * | 105: message[CALL_FUNCTION] = 1 + * | 105: doorbell_global_ipi(42): + * | 105: kvmppc_set_host_ipi(42) + * | // RE-ORDERED STORE COMPLETES + * -> 42: kvmppc_clear_host_ipi(42) + * 42: // returns to executing guest + * 105: ppc_msgsnd_sync()/smp_mb() + * 105: ppc_msgsnd() -> 42 + * 42: local_paca->kvm_hstate.host_ipi == 0 // IPI ignored + * 105: // hangs waiting on 42 to process messages/call_single_queue + */ +static inline void kvmppc_set_host_ipi(int cpu) { - paca_ptrs[cpu]->kvm_hstate.host_ipi = host_ipi; + /* + * order stores of IPI messages vs. setting of host_ipi flag + * + * pairs with the barrier in kvmppc_clear_host_ipi() + */ + smp_mb(); + paca_ptrs[cpu]->kvm_hstate.host_ipi = 1; +} + +static inline void kvmppc_clear_host_ipi(int cpu) +{ + paca_ptrs[cpu]->kvm_hstate.host_ipi = 0; + /* + * order clearing of host_ipi flag vs. processing of IPI messages + * + * pairs with the barrier in kvmppc_set_host_ipi() + */ + smp_mb(); } static inline void kvmppc_fast_vcpu_kick(struct kvm_vcpu *vcpu) @@ -486,7 +577,10 @@ static inline u32 kvmppc_get_xics_latch(void) return 0; } -static inline void kvmppc_set_host_ipi(int cpu, u8 host_ipi) +static inline void kvmppc_set_host_ipi(int cpu) +{} + +static inline void kvmppc_clear_host_ipi(int cpu) {} static inline void kvmppc_fast_vcpu_kick(struct kvm_vcpu *vcpu) |