[PATCH v2 16/37] KVM: PPC: Book3S HV P9: Stop handling hcalls in real-mode in the P9 path

[Nicholas Piggin]

Excerpts from Cédric Le Goater's message of February 26, 2021 12:51 am:
> On 2/25/21 2:46 PM, 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 at gmail.com>
>> ---
>>  arch/powerpc/include/asm/kvm_ppc.h      |  5 +++++
>>  arch/powerpc/kvm/book3s_hv.c            | 25 ++++++++++++++++++++++---
>>  arch/powerpc/kvm/book3s_hv_rmhandlers.S |  5 +++++
>>  arch/powerpc/kvm/book3s_xive.c          | 25 +++++++++++++++++++++++++
>>  4 files changed, 57 insertions(+), 3 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);
> 
> I can not find this routine. Is it missing or coming later in the patchset ? 

Yeah it leaked into a later patch but it belongs here. I'll fix it.

Thanks,
Nick