Excerpts from Alexey Kardashevskiy's message of March 23, 2021 7:02 pm:
>
>
> On 23/03/2021 12:02, Nicholas Piggin wrote:
>> In the interest of minimising the amount of code that is run in
>> "real-mode", don't handle hcalls in real mode in the P9 path.
>>
>> POWER8 and earlier are much more expensive to exit from HV real mode
>> and switch to host mode, because on those processors HV interrupts get
>> to the hypervisor with the MMU off, and the other threads in the core
>> need to be pulled out of the guest, and SLBs all need to be saved,
>> ERATs invalidated, and host SLB reloaded before the MMU is re-enabled
>> in host mode. Hash guests also require a lot of hcalls to run. The
>> XICS interrupt controller requires hcalls to run.
>>
>> By contrast, POWER9 has independent thread switching, and in radix mode
>> the hypervisor is already in a host virtual memory mode when the HV
>> interrupt is taken. Radix + xive guests don't need hcalls to handle
>> interrupts or manage translations.
>>
>> So it's much less important to handle hcalls in real mode in P9.
>>
>> Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx>
>> ---
>> arch/powerpc/include/asm/kvm_ppc.h | 5 ++
>> arch/powerpc/kvm/book3s_hv.c | 57 ++++++++++++++++----
>> arch/powerpc/kvm/book3s_hv_rmhandlers.S | 5 ++
>> arch/powerpc/kvm/book3s_xive.c | 70 +++++++++++++++++++++++++
>> 4 files changed, 127 insertions(+), 10 deletions(-)
>>
>> diff --git a/arch/powerpc/include/asm/kvm_ppc.h b/arch/powerpc/include/asm/kvm_ppc.h
>> index 73b1ca5a6471..db6646c2ade2 100644
>> --- a/arch/powerpc/include/asm/kvm_ppc.h
>> +++ b/arch/powerpc/include/asm/kvm_ppc.h
>> @@ -607,6 +607,7 @@ extern void kvmppc_free_pimap(struct kvm *kvm);
>> extern int kvmppc_xics_rm_complete(struct kvm_vcpu *vcpu, u32 hcall);
>> extern void kvmppc_xics_free_icp(struct kvm_vcpu *vcpu);
>> extern int kvmppc_xics_hcall(struct kvm_vcpu *vcpu, u32 cmd);
>> +extern int kvmppc_xive_xics_hcall(struct kvm_vcpu *vcpu, u32 req);
>> extern u64 kvmppc_xics_get_icp(struct kvm_vcpu *vcpu);
>> extern int kvmppc_xics_set_icp(struct kvm_vcpu *vcpu, u64 icpval);
>> extern int kvmppc_xics_connect_vcpu(struct kvm_device *dev,
>> @@ -639,6 +640,8 @@ static inline int kvmppc_xics_enabled(struct kvm_vcpu *vcpu)
>> static inline void kvmppc_xics_free_icp(struct kvm_vcpu *vcpu) { }
>> static inline int kvmppc_xics_hcall(struct kvm_vcpu *vcpu, u32 cmd)
>> { return 0; }
>> +static inline int kvmppc_xive_xics_hcall(struct kvm_vcpu *vcpu, u32 req)
>> + { return 0; }
>> #endif
>>
>> #ifdef CONFIG_KVM_XIVE
>> @@ -673,6 +676,7 @@ extern int kvmppc_xive_set_irq(struct kvm *kvm, int irq_source_id, u32 irq,
>> int level, bool line_status);
>> extern void kvmppc_xive_push_vcpu(struct kvm_vcpu *vcpu);
>> extern void kvmppc_xive_pull_vcpu(struct kvm_vcpu *vcpu);
>> +extern void kvmppc_xive_cede_vcpu(struct kvm_vcpu *vcpu);
>>
>> static inline int kvmppc_xive_enabled(struct kvm_vcpu *vcpu)
>> {
>> @@ -714,6 +718,7 @@ static inline int kvmppc_xive_set_irq(struct kvm *kvm, int irq_source_id, u32 ir
>> int level, bool line_status) { return -ENODEV; }
>> static inline void kvmppc_xive_push_vcpu(struct kvm_vcpu *vcpu) { }
>> static inline void kvmppc_xive_pull_vcpu(struct kvm_vcpu *vcpu) { }
>> +static inline void kvmppc_xive_cede_vcpu(struct kvm_vcpu *vcpu) { }
>>
>> static inline int kvmppc_xive_enabled(struct kvm_vcpu *vcpu)
>> { return 0; }
>> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
>> index fa7614c37e08..17739aaee3d8 100644
>> --- a/arch/powerpc/kvm/book3s_hv.c
>> +++ b/arch/powerpc/kvm/book3s_hv.c
>> @@ -1142,12 +1142,13 @@ int kvmppc_pseries_do_hcall(struct kvm_vcpu *vcpu)
>> }
>>
>> /*
>> - * Handle H_CEDE in the nested virtualization case where we haven't
>> - * called the real-mode hcall handlers in book3s_hv_rmhandlers.S.
>> + * Handle H_CEDE in the P9 path where we don't call the real-mode hcall
>> + * handlers in book3s_hv_rmhandlers.S.
>> + *
>> * This has to be done early, not in kvmppc_pseries_do_hcall(), so
>> * that the cede logic in kvmppc_run_single_vcpu() works properly.
>> */
>> -static void kvmppc_nested_cede(struct kvm_vcpu *vcpu)
>> +static void kvmppc_cede(struct kvm_vcpu *vcpu)
>> {
>> vcpu->arch.shregs.msr |= MSR_EE;
>> vcpu->arch.ceded = 1;
>> @@ -1403,9 +1404,15 @@ static int kvmppc_handle_exit_hv(struct kvm_vcpu *vcpu,
>> /* hcall - punt to userspace */
>> int i;
>>
>> - /* hypercall with MSR_PR has already been handled in rmode,
>> - * and never reaches here.
>> - */
>> + if (unlikely(vcpu->arch.shregs.msr & MSR_PR)) {
>> + /*
>> + * Guest userspace executed sc 1, reflect it back as a
>> + * privileged program check interrupt.
>> + */
>> + kvmppc_core_queue_program(vcpu, SRR1_PROGPRIV);
>> + r = RESUME_GUEST;
>> + break;
>> + }
>>
>> run->papr_hcall.nr = kvmppc_get_gpr(vcpu, 3);
>> for (i = 0; i < 9; ++i)
>> @@ -3663,6 +3670,12 @@ static int kvmhv_load_hv_regs_and_go(struct kvm_vcpu *vcpu, u64 time_limit,
>> return trap;
>> }
>>
>> +static inline bool hcall_is_xics(unsigned long req)
>> +{
>> + return (req == H_EOI || req == H_CPPR || req == H_IPI ||
>> + req == H_IPOLL || req == H_XIRR || req == H_XIRR_X);
>
> Do not need braces :)
>
>
>> +}
>> +
>> /*
>> * Virtual-mode guest entry for POWER9 and later when the host and
>> * guest are both using the radix MMU. The LPIDR has already been set.
>> @@ -3774,15 +3787,36 @@ static int kvmhv_p9_guest_entry(struct kvm_vcpu *vcpu, u64 time_limit,
>> /* H_CEDE has to be handled now, not later */
>> if (trap == BOOK3S_INTERRUPT_SYSCALL && !vcpu->arch.nested &&
>> kvmppc_get_gpr(vcpu, 3) == H_CEDE) {
>> - kvmppc_nested_cede(vcpu);
>> + kvmppc_cede(vcpu);
>> kvmppc_set_gpr(vcpu, 3, 0);
>> trap = 0;
>> }
>> } else {
>> kvmppc_xive_push_vcpu(vcpu);
>> trap = kvmhv_load_hv_regs_and_go(vcpu, time_limit, lpcr);
>> + if (trap == BOOK3S_INTERRUPT_SYSCALL && !vcpu->arch.nested &&
>> + !(vcpu->arch.shregs.msr & MSR_PR)) {
>> + unsigned long req = kvmppc_get_gpr(vcpu, 3);
>> +
>> + /* H_CEDE has to be handled now, not later */
>> + if (req == H_CEDE) {
>> + kvmppc_cede(vcpu);
>> + kvmppc_xive_cede_vcpu(vcpu); /* may un-cede */
>> + kvmppc_set_gpr(vcpu, 3, 0);
>> + trap = 0;
>> +
>> + /* XICS hcalls must be handled before xive is pulled */
>> + } else if (hcall_is_xics(req)) {
>> + int ret;
>> +
>> + ret = kvmppc_xive_xics_hcall(vcpu, req);
>> + if (ret != H_TOO_HARD) {
>> + kvmppc_set_gpr(vcpu, 3, ret);
>> + trap = 0;
>> + }
>> + }
>> + }
>> kvmppc_xive_pull_vcpu(vcpu);
>> -
>> }
>>
>> vcpu->arch.slb_max = 0;
>> @@ -4442,8 +4476,11 @@ static int kvmppc_vcpu_run_hv(struct kvm_vcpu *vcpu)
>> else
>> r = kvmppc_run_vcpu(vcpu);
>>
>> - if (run->exit_reason == KVM_EXIT_PAPR_HCALL &&
>> - !(vcpu->arch.shregs.msr & MSR_PR)) {
>> + if (run->exit_reason == KVM_EXIT_PAPR_HCALL) {
>> + if (WARN_ON_ONCE(vcpu->arch.shregs.msr & MSR_PR)) {
>> + r = RESUME_GUEST;
>> + continue;
>> + }
>> trace_kvm_hcall_enter(vcpu);
>> r = kvmppc_pseries_do_hcall(vcpu);
>> trace_kvm_hcall_exit(vcpu, r);
>> diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
>> index c11597f815e4..2d0d14ed1d92 100644
>> --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
>> +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
>> @@ -1397,9 +1397,14 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
>> mr r4,r9
>> bge fast_guest_return
>> 2:
>> + /* If we came in through the P9 short path, no real mode hcalls */
>> + lwz r0, STACK_SLOT_SHORT_PATH(r1)
>> + cmpwi r0, 0
>> + bne no_try_real
>
>
> btw is mmu on at this point? or it gets enabled by rfid at the end of
> guest_exit_short_path?
Hash guest it's off. Radix guest it can be on or off depending on the
interrupt type and MSR and LPCR[AIL] values.
Thanks,
Nick
