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SubjectRe: [PATCH 3/3] KVM: x86: do not scan IRR twice on APICv vmentry
On Tue, Sep 27, 2016 at 11:20:13PM +0200, Paolo Bonzini wrote:
> Calling apic_find_highest_irr results in IRR being scanned twice,
> once in vmx_sync_pir_from_irr and once in apic_search_irr. Change
> vcpu_enter_guest to use sync_pir_from_irr (with a new argument to
> trigger the RVI write), and let sync_pir_from_irr get the new RVI
> directly from kvm_apic_update_irr.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Acked-by: Michael S. Tsirkin <mst@redhat.com>

> ---
> arch/x86/include/asm/kvm_host.h | 2 +-
> arch/x86/kvm/lapic.c | 25 ++++++++++++++++---------
> arch/x86/kvm/lapic.h | 4 ++--
> arch/x86/kvm/svm.c | 2 +-
> arch/x86/kvm/vmx.c | 25 ++++++++++++++-----------
> arch/x86/kvm/x86.c | 7 +++----
> 6 files changed, 37 insertions(+), 28 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 4b20f7304b9c..f73eea243567 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -941,7 +941,7 @@ struct kvm_x86_ops {
> void (*set_virtual_x2apic_mode)(struct kvm_vcpu *vcpu, bool set);
> void (*set_apic_access_page_addr)(struct kvm_vcpu *vcpu, hpa_t hpa);
> void (*deliver_posted_interrupt)(struct kvm_vcpu *vcpu, int vector);
> - void (*sync_pir_to_irr)(struct kvm_vcpu *vcpu);
> + void (*sync_pir_to_irr)(struct kvm_vcpu *vcpu, bool sync_rvi);
> int (*set_tss_addr)(struct kvm *kvm, unsigned int addr);
> int (*get_tdp_level)(void);
> u64 (*get_mt_mask)(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio);
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index be8b7ad56dd1..85b79b90e3d0 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -317,7 +317,7 @@ static int find_highest_vector(void *bitmap)
> vec >= 0; vec -= APIC_VECTORS_PER_REG) {
> reg = bitmap + REG_POS(vec);
> if (*reg)
> - return fls(*reg) - 1 + vec;
> + return __fls(*reg) + vec;
> }
>
> return -1;

We checked that *reg is != 0 so __fls is safe.
It's a correct micro-optimization but why stick it in this patch?

> @@ -337,25 +337,32 @@ static u8 count_vectors(void *bitmap)
> return count;
> }
>
> -void __kvm_apic_update_irr(u32 *pir, void *regs)
> +int __kvm_apic_update_irr(u32 *pir, void *regs)
> {
> - u32 i, pir_val;
> + u32 i, vec;
> + u32 pir_val, irr_val;
> + int max_irr = -1;
>
> - for (i = 0; i <= 7; i++) {
> + for (i = vec = 0; i <= 7; i++, vec += 32) {
> pir_val = READ_ONCE(pir[i]);
> + irr_val = *((u32 *)(regs + APIC_IRR + i * 0x10));
> if (pir_val) {
> - pir_val = xchg(&pir[i], 0);
> - *((u32 *)(regs + APIC_IRR + i * 0x10)) |= pir_val;
> + irr_val |= xchg(&pir[i], 0);
> + *((u32 *)(regs + APIC_IRR + i * 0x10)) = irr_val;
> }
> + if (irr_val)
> + max_irr = __fls(irr_val) + vec;
> }
> +
> + return max_irr;
> }
> EXPORT_SYMBOL_GPL(__kvm_apic_update_irr);
>
> -void kvm_apic_update_irr(struct kvm_vcpu *vcpu, u32 *pir)
> +int kvm_apic_update_irr(struct kvm_vcpu *vcpu, u32 *pir)
> {
> struct kvm_lapic *apic = vcpu->arch.apic;
>
> - __kvm_apic_update_irr(pir, apic->regs);
> + return __kvm_apic_update_irr(pir, apic->regs);
> }
> EXPORT_SYMBOL_GPL(kvm_apic_update_irr);
>
> @@ -376,7 +383,7 @@ static inline int apic_find_highest_irr(struct kvm_lapic *apic)
> return -1;
>
> if (apic->vcpu->arch.apicv_active)
> - kvm_x86_ops->sync_pir_to_irr(apic->vcpu);
> + kvm_x86_ops->sync_pir_to_irr(apic->vcpu, false);
> result = apic_search_irr(apic);
> ASSERT(result == -1 || result >= 16);
>
> diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
> index f60d01c29d51..fc72828c3782 100644
> --- a/arch/x86/kvm/lapic.h
> +++ b/arch/x86/kvm/lapic.h
> @@ -70,8 +70,8 @@ int kvm_lapic_reg_read(struct kvm_lapic *apic, u32 offset, int len,
> bool kvm_apic_match_dest(struct kvm_vcpu *vcpu, struct kvm_lapic *source,
> int short_hand, unsigned int dest, int dest_mode);
>
> -void __kvm_apic_update_irr(u32 *pir, void *regs);
> -void kvm_apic_update_irr(struct kvm_vcpu *vcpu, u32 *pir);
> +int __kvm_apic_update_irr(u32 *pir, void *regs);
> +int kvm_apic_update_irr(struct kvm_vcpu *vcpu, u32 *pir);
> int kvm_apic_set_irq(struct kvm_vcpu *vcpu, struct kvm_lapic_irq *irq,
> struct dest_map *dest_map);
> int kvm_apic_local_deliver(struct kvm_lapic *apic, int lvt_type);
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 9b4221471e3d..60e53fa2b554 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -4383,7 +4383,7 @@ static void svm_load_eoi_exitmap(struct kvm_vcpu *vcpu, u64 *eoi_exit_bitmap)
> return;
> }
>
> -static void svm_sync_pir_to_irr(struct kvm_vcpu *vcpu)
> +static void svm_sync_pir_to_irr(struct kvm_vcpu *vcpu, bool sync_rvi)
> {
> return;
> }
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 207b9aa32915..1edefab54d01 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -4852,17 +4852,6 @@ static void vmx_deliver_posted_interrupt(struct kvm_vcpu *vcpu, int vector)
> kvm_vcpu_kick(vcpu);
> }
>
> -static void vmx_sync_pir_to_irr(struct kvm_vcpu *vcpu)
> -{
> - struct vcpu_vmx *vmx = to_vmx(vcpu);
> -
> - if (!pi_test_on(&vmx->pi_desc) ||
> - !pi_test_and_clear_on(&vmx->pi_desc))
> - return;
> -
> - kvm_apic_update_irr(vcpu, vmx->pi_desc.pir);
> -}
> -
> /*
> * Set up the vmcs's constant host-state fields, i.e., host-state fields that
> * will not change in the lifetime of the guest.
> @@ -8609,6 +8598,20 @@ static void vmx_hwapic_irr_update(struct kvm_vcpu *vcpu, int max_irr)
> }
> }
>
> +static void vmx_sync_pir_to_irr(struct kvm_vcpu *vcpu, bool sync_rvi)
> +{
> + struct vcpu_vmx *vmx = to_vmx(vcpu);
> + int max_irr;
> +
> + if (!pi_test_on(&vmx->pi_desc) ||
> + !pi_test_and_clear_on(&vmx->pi_desc))
> + return;
> +
> + max_irr = kvm_apic_update_irr(vcpu, vmx->pi_desc.pir);
> + if (sync_rvi)
> + vmx_hwapic_irr_update(vcpu, max_irr);
> +}
> +
> static void vmx_load_eoi_exitmap(struct kvm_vcpu *vcpu, u64 *eoi_exit_bitmap)
> {
> if (!kvm_vcpu_apicv_active(vcpu))
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 604cfbfc5bee..148e14fdc55d 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2821,7 +2821,7 @@ static int kvm_vcpu_ioctl_get_lapic(struct kvm_vcpu *vcpu,
> struct kvm_lapic_state *s)
> {
> if (vcpu->arch.apicv_active)
> - kvm_x86_ops->sync_pir_to_irr(vcpu);
> + kvm_x86_ops->sync_pir_to_irr(vcpu, false);
>
> return kvm_apic_get_state(vcpu, s);
> }
> @@ -6448,7 +6448,7 @@ static void vcpu_scan_ioapic(struct kvm_vcpu *vcpu)
> kvm_scan_ioapic_routes(vcpu, vcpu->arch.ioapic_handled_vectors);
> else {
> if (vcpu->arch.apicv_active)
> - kvm_x86_ops->sync_pir_to_irr(vcpu);
> + kvm_x86_ops->sync_pir_to_irr(vcpu, false);
> kvm_ioapic_scan_entry(vcpu, vcpu->arch.ioapic_handled_vectors);
> }
> bitmap_or((ulong *)eoi_exit_bitmap, vcpu->arch.ioapic_handled_vectors,
> @@ -6611,8 +6611,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> * virtual interrupt delivery.
> */
> if (vcpu->arch.apicv_active)
> - kvm_x86_ops->hwapic_irr_update(vcpu,
> - kvm_lapic_find_highest_irr(vcpu));
> + kvm_x86_ops->sync_pir_to_irr(vcpu, true);
> }
>
> if (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win) {
> --
> 1.8.3.1

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