Li RongQing <lirongqing@xxxxxxxxx> writes:
> merge pv_eoi_get_pending and pv_eoi_clr_pending into a single
> function pv_eoi_test_and_clear_pending, which returns and clear
> the value of the pending bit.
>
> and clear pv eoi pending bit only when it is set, to avoid calling
> pv_eoi_put_user(), this can speed about 300 nsec on AMD EPYC most
> of the time
>
> and make pv_eoi_set_pending as inline as there is only one user
Compiler is likely smart enough to inline static functions with a single
user anyway.
>
> Suggested-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> Suggested-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Signed-off-by: Li RongQing <lirongqing@xxxxxxxxx>
> ---
> diff with v1:
> merge as pv_eoi_test_and_clear_pending
> add inline for pv_eoi_set_pending
>
> arch/x86/kvm/lapic.c | 47 +++++++++++++++++++++++------------------------
> 1 files changed, 23 insertions(+), 24 deletions(-)
>
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 76fb009..4da5db8 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -673,18 +673,7 @@ static inline bool pv_eoi_enabled(struct kvm_vcpu *vcpu)
> return vcpu->arch.pv_eoi.msr_val & KVM_MSR_ENABLED;
> }
>
> -static bool pv_eoi_get_pending(struct kvm_vcpu *vcpu)
> -{
> - u8 val;
> - if (pv_eoi_get_user(vcpu, &val) < 0) {
> - printk(KERN_WARNING "Can't read EOI MSR value: 0x%llx\n",
> - (unsigned long long)vcpu->arch.pv_eoi.msr_val);
> - return false;
> - }
> - return val & KVM_PV_EOI_ENABLED;
> -}
> -
> -static void pv_eoi_set_pending(struct kvm_vcpu *vcpu)
> +static inline void pv_eoi_set_pending(struct kvm_vcpu *vcpu)
> {
> if (pv_eoi_put_user(vcpu, KVM_PV_EOI_ENABLED) < 0) {
> printk(KERN_WARNING "Can't set EOI MSR value: 0x%llx\n",
> @@ -694,14 +683,31 @@ static void pv_eoi_set_pending(struct kvm_vcpu *vcpu)
> __set_bit(KVM_APIC_PV_EOI_PENDING, &vcpu->arch.apic_attention);
> }
>
> -static void pv_eoi_clr_pending(struct kvm_vcpu *vcpu)
> +static inline bool pv_eoi_test_and_clr_pending(struct kvm_vcpu *vcpu)
> {
> - if (pv_eoi_put_user(vcpu, KVM_PV_EOI_DISABLED) < 0) {
> + u8 val;
> +
> + if (pv_eoi_get_user(vcpu, &val) < 0) {
> + printk(KERN_WARNING "Can't read EOI MSR value: 0x%llx\n",
> + (unsigned long long)vcpu->arch.pv_eoi.msr_val);
pr_warn() would probably be a better choice but looking at this makes me
wonder: isn't it triggerable by the guest? I think it is when the value
written to MSR_KVM_PV_EOI_EN is bogus and this is bad: we don't even
ratelimit these messages! I think this printk() needs to be dropped.
> + return false;
> + }
> +
> + val &= KVM_PV_EOI_ENABLED;
> +
> + /*
> + * Clear pending bit in any case: it will be set again on vmentry.
> + * While this might not be ideal from performance point of view,
> + * this makes sure pv eoi is only enabled when we know it's safe.
> + */
> + if (val && pv_eoi_put_user(vcpu, KVM_PV_EOI_DISABLED) < 0) {
> printk(KERN_WARNING "Can't clear EOI MSR value: 0x%llx\n",
> (unsigned long long)vcpu->arch.pv_eoi.msr_val);
... and this one, probably, too.
> - return;
> + return false;
> }
> __clear_bit(KVM_APIC_PV_EOI_PENDING, &vcpu->arch.apic_attention);
> +
> + return !!val;
> }
>
> static int apic_has_interrupt_for_ppr(struct kvm_lapic *apic, u32 ppr)
> @@ -2673,7 +2679,6 @@ void __kvm_migrate_apic_timer(struct kvm_vcpu *vcpu)
> static void apic_sync_pv_eoi_from_guest(struct kvm_vcpu *vcpu,
> struct kvm_lapic *apic)
> {
> - bool pending;
> int vector;
> /*
> * PV EOI state is derived from KVM_APIC_PV_EOI_PENDING in host
> @@ -2687,14 +2692,8 @@ static void apic_sync_pv_eoi_from_guest(struct kvm_vcpu *vcpu,
> * -> host enabled PV EOI, guest executed EOI.
> */
> BUG_ON(!pv_eoi_enabled(vcpu));
> - pending = pv_eoi_get_pending(vcpu);
> - /*
> - * Clear pending bit in any case: it will be set again on vmentry.
> - * While this might not be ideal from performance point of view,
> - * this makes sure pv eoi is only enabled when we know it's safe.
> - */
> - pv_eoi_clr_pending(vcpu);
> - if (pending)
> +
> + if (pv_eoi_test_and_clr_pending(vcpu))
> return;
> vector = apic_set_eoi(apic);
> trace_kvm_pv_eoi(apic, vector);
--
Vitaly
