Message ID | 1413487800-7162-8-git-send-email-kernelfans@gmail.com (mailing list archive) |
---|---|
State | RFC |
Headers | show |
Hi Liu, On 10/17/2014 12:59 AM, kernelfans@gmail.com wrote: > To enter guest, primary hwtherad schedules the stopper func on > secondary threads and force them into NAP mode. > When exit to host,secondary threads hardcode to restore the stack, > then switch back to the stopper func, i.e host. > > Signed-off-by: Liu Ping Fan <pingfank@linux.vnet.ibm.com> > --- > arch/powerpc/kvm/book3s_hv.c | 15 +++++++++++++++ > arch/powerpc/kvm/book3s_hv_rmhandlers.S | 34 +++++++++++++++++++++++++++++++++ > 2 files changed, 49 insertions(+) > > diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c > index ba258c8..4348abd 100644 > --- a/arch/powerpc/kvm/book3s_hv.c > +++ b/arch/powerpc/kvm/book3s_hv.c > @@ -1486,6 +1486,21 @@ static void kvmppc_remove_runnable(struct kvmppc_vcore *vc, > list_del(&vcpu->arch.run_list); > } > > +#ifdef KVMPPC_ENABLE_SECONDARY > + > +extern void kvmppc_secondary_stopper_enter(); > + > +static int kvmppc_secondary_stopper(void *data) > +{ > + int cpu =smp_processor_id(); > + struct paca_struct *lpaca = get_paca(); > + BUG_ON(!(cpu%thread_per_core)); > + > + kvmppc_secondary_stopper_enter(); > +} > + > +#endif > + > static int kvmppc_grab_hwthread(int cpu) > { > struct paca_struct *tpaca; > diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S > index d5594b0..254038b 100644 > --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S > +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S > @@ -349,7 +349,41 @@ kvm_do_nap: > > #ifdef PPCKVM_ENABLE_SECONDARY > kvm_secondary_exit_trampoline: > + > + /* all register is free to use, later kvmppc_secondary_stopper_exit set up them*/ > + //loop-wait for the primary to signal that host env is ready > + > + LOAD_REG_ADDR(r5, kvmppc_secondary_stopper_exit) > + /* fixme, load msr from lpaca stack */ > + li r6, MSR_IR | MSR_DR > + mtsrr0 r5 > + mtsrr1 r6 > + RFI > + > +_GLOBAL_TOC(kvmppc_secondary_stopper_enter) > + mflr r0 > + std r0, PPC_LR_STKOFF(r1) > + stdu r1, -112(r1) > + > + /* fixme: store other register such as msr */ > + > + /* prevent us to enter kernel */ > + li r0, 1 > + stb r0, HSTATE_HWTHREAD_REQ(r13) > + /* tell the primary that we are ready */ > + li r0,KVM_HWTHREAD_IN_KERNEL > + stb r0,HSTATE_HWTHREAD_STATE(r13) > + nap > b . This does not look right. Let me explain. We can get hypervisor decrementer interrupts on the secondary threads since they are online. And we would ideally want to handle them. They could be scheduler tick interrupts or some timer queued on that thread could have fired. If it is a scheduler tick, we would want to exit to host to schedule the next task if the timeslice of the vcpu running on the secondary thread is over. To the best of my understanding, this is what I can tell happens when we get a hypervisor decrementer interrupt in the guest. We call all threads in the core to exit to the kernel. The secondaries now return to the code in idle_power7.S where the wakeup from idle path takes effect. Then we do an rfid which lands after the nap code above. And we spin. From your above code you seem to be indicating that you do not want the secondary threads to exit to the kernel once they are made to run guest for the first time. Is this right? Or am I missing something ? Moreover the changelog in [patch 10/11] says that you cease the scheduler. This pushes me to think that you do not expect the scheduler to run on the secondary threads ever again after you have launched the guest. This does not look right to me. Regards Preeti U Murthy
On 10/17/2014 12:59 AM, kernelfans@gmail.com wrote: > To enter guest, primary hwtherad schedules the stopper func on > secondary threads and force them into NAP mode. > When exit to host,secondary threads hardcode to restore the stack, > then switch back to the stopper func, i.e host. > > Signed-off-by: Liu Ping Fan <pingfank@linux.vnet.ibm.com> > --- > arch/powerpc/kvm/book3s_hv.c | 15 +++++++++++++++ > arch/powerpc/kvm/book3s_hv_rmhandlers.S | 34 +++++++++++++++++++++++++++++++++ > 2 files changed, 49 insertions(+) > > diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c > index ba258c8..4348abd 100644 > --- a/arch/powerpc/kvm/book3s_hv.c > +++ b/arch/powerpc/kvm/book3s_hv.c > @@ -1486,6 +1486,21 @@ static void kvmppc_remove_runnable(struct kvmppc_vcore *vc, > list_del(&vcpu->arch.run_list); > } > > +#ifdef KVMPPC_ENABLE_SECONDARY > + > +extern void kvmppc_secondary_stopper_enter(); > + > +static int kvmppc_secondary_stopper(void *data) > +{ > + int cpu =smp_processor_id(); > + struct paca_struct *lpaca = get_paca(); > + BUG_ON(!(cpu%thread_per_core)); > + > + kvmppc_secondary_stopper_enter(); > +} > + > +#endif > + > static int kvmppc_grab_hwthread(int cpu) > { > struct paca_struct *tpaca; > diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S > index d5594b0..254038b 100644 > --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S > +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S > @@ -349,7 +349,41 @@ kvm_do_nap: > > #ifdef PPCKVM_ENABLE_SECONDARY > kvm_secondary_exit_trampoline: > + > + /* all register is free to use, later kvmppc_secondary_stopper_exit set up them*/ > + //loop-wait for the primary to signal that host env is ready > + > + LOAD_REG_ADDR(r5, kvmppc_secondary_stopper_exit) > + /* fixme, load msr from lpaca stack */ > + li r6, MSR_IR | MSR_DR > + mtsrr0 r5 > + mtsrr1 r6 > + RFI > + > +_GLOBAL_TOC(kvmppc_secondary_stopper_enter) > + mflr r0 > + std r0, PPC_LR_STKOFF(r1) > + stdu r1, -112(r1) > + > + /* fixme: store other register such as msr */ > + > + /* prevent us to enter kernel */ > + li r0, 1 > + stb r0, HSTATE_HWTHREAD_REQ(r13) > + /* tell the primary that we are ready */ > + li r0,KVM_HWTHREAD_IN_KERNEL > + stb r0,HSTATE_HWTHREAD_STATE(r13) > + nap > b . I see a fundamental issues with this design. Note that the secondaries are still capable of getting IPIs, timer interrupts and scheduler interrupts in nap. Scheduling ticks do not get stopped just because we nap. So the primary thread cannot assume that the secondaries will wait in nap until it has switched to guest context. There will definitely be race conditions here between primary switching context and the secondary handling some interrupt in virtual mode. So your answer to above could be that we are preventing the secondaries from entering the kernel by setting the HSTATE_HWTHREAD_REQ above. But we cannot do this because the secondary thread is as alive and kicking as the primary thread on the host. There can be hrtimers queued, there may be an IPI from a thread in another core. We cannot ignore handling them while we wait for the primary thread to switch context. There is also a bug as far as I can see with having a b . after nap. I mentioned that in one of my earlier replies to this patch. Regards Preeti U Murthy > + > +/* enter with vmode */ > +kvmppc_secondary_stopper_exit: > + /* fixme, restore the stack which we store on lpaca */ > + > + ld r0, 112+PPC_LR_STKOFF(r1) > + addi r1, r1, 112 > + mtlr r0 > + blr > #endif > > /****************************************************************************** >
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c index ba258c8..4348abd 100644 --- a/arch/powerpc/kvm/book3s_hv.c +++ b/arch/powerpc/kvm/book3s_hv.c @@ -1486,6 +1486,21 @@ static void kvmppc_remove_runnable(struct kvmppc_vcore *vc, list_del(&vcpu->arch.run_list); } +#ifdef KVMPPC_ENABLE_SECONDARY + +extern void kvmppc_secondary_stopper_enter(); + +static int kvmppc_secondary_stopper(void *data) +{ + int cpu =smp_processor_id(); + struct paca_struct *lpaca = get_paca(); + BUG_ON(!(cpu%thread_per_core)); + + kvmppc_secondary_stopper_enter(); +} + +#endif + static int kvmppc_grab_hwthread(int cpu) { struct paca_struct *tpaca; diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S index d5594b0..254038b 100644 --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S @@ -349,7 +349,41 @@ kvm_do_nap: #ifdef PPCKVM_ENABLE_SECONDARY kvm_secondary_exit_trampoline: + + /* all register is free to use, later kvmppc_secondary_stopper_exit set up them*/ + //loop-wait for the primary to signal that host env is ready + + LOAD_REG_ADDR(r5, kvmppc_secondary_stopper_exit) + /* fixme, load msr from lpaca stack */ + li r6, MSR_IR | MSR_DR + mtsrr0 r5 + mtsrr1 r6 + RFI + +_GLOBAL_TOC(kvmppc_secondary_stopper_enter) + mflr r0 + std r0, PPC_LR_STKOFF(r1) + stdu r1, -112(r1) + + /* fixme: store other register such as msr */ + + /* prevent us to enter kernel */ + li r0, 1 + stb r0, HSTATE_HWTHREAD_REQ(r13) + /* tell the primary that we are ready */ + li r0,KVM_HWTHREAD_IN_KERNEL + stb r0,HSTATE_HWTHREAD_STATE(r13) + nap b . + +/* enter with vmode */ +kvmppc_secondary_stopper_exit: + /* fixme, restore the stack which we store on lpaca */ + + ld r0, 112+PPC_LR_STKOFF(r1) + addi r1, r1, 112 + mtlr r0 + blr #endif /******************************************************************************
To enter guest, primary hwtherad schedules the stopper func on secondary threads and force them into NAP mode. When exit to host,secondary threads hardcode to restore the stack, then switch back to the stopper func, i.e host. Signed-off-by: Liu Ping Fan <pingfank@linux.vnet.ibm.com> --- arch/powerpc/kvm/book3s_hv.c | 15 +++++++++++++++ arch/powerpc/kvm/book3s_hv_rmhandlers.S | 34 +++++++++++++++++++++++++++++++++ 2 files changed, 49 insertions(+)