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Message-ID: <20120516015519.GA4529@amt.cnet>
Date: Tue, 15 May 2012 22:55:19 -0300
From: Marcelo Tosatti <mtosatti@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: x86@...nel.org, kvm@...r.kernel.org,
Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>, Avi Kivity <avi@...hat.com>,
gleb@...hat.com, Linus Torvalds <torvalds@...ux-foundation.org>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3 7/8] kvm: host side for eoi optimization
On Tue, May 15, 2012 at 05:36:19PM +0300, Michael S. Tsirkin wrote:
> Implementation of PV EOI using shared memory.
> This reduces the number of exits an interrupt
> causes as much as by half.
>
> The idea is simple: there's a bit, per APIC, in guest memory,
> that tells the guest that it does not need EOI.
> We set it before injecting an interrupt and clear
> before injecting a nested one. Guest tests it using
> a test and clear operation - this is necessary
> so that host can detect interrupt nesting -
> and if set, it can skip the EOI MSR.
>
> There's a new MSR to set the address of said register
> in guest memory. Otherwise not much changed:
> - Guest EOI is not required
> - Register is tested & ISR is automatically cleared on exit
> For tetsing results see description of patch 7 of the series.
>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---
> arch/x86/include/asm/kvm_host.h | 6 ++
> arch/x86/include/asm/kvm_para.h | 2 +
> arch/x86/kvm/cpuid.c | 1 +
> arch/x86/kvm/irq.c | 2 +-
> arch/x86/kvm/lapic.c | 110 +++++++++++++++++++++++++++++++++++++--
> arch/x86/kvm/lapic.h | 2 +
> arch/x86/kvm/trace.h | 34 ++++++++++++
> arch/x86/kvm/x86.c | 8 +++-
> 8 files changed, 158 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 32297f2..7673f4d 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -174,6 +174,7 @@ enum {
>
> /* apic attention bits */
> #define KVM_APIC_CHECK_VAPIC 0
> +#define KVM_APIC_EOI_PENDING 1
>
> /*
> * We don't want allocation failures within the mmu code, so we preallocate
> @@ -485,6 +486,11 @@ struct kvm_vcpu_arch {
> u64 length;
> u64 status;
> } osvw;
> +
> + struct {
> + u64 msr_val;
> + struct gfn_to_hva_cache data;
> + } eoi;
> };
>
> struct kvm_lpage_info {
> diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
> index 734c376..195840d 100644
> --- a/arch/x86/include/asm/kvm_para.h
> +++ b/arch/x86/include/asm/kvm_para.h
> @@ -22,6 +22,7 @@
> #define KVM_FEATURE_CLOCKSOURCE2 3
> #define KVM_FEATURE_ASYNC_PF 4
> #define KVM_FEATURE_STEAL_TIME 5
> +#define KVM_FEATURE_EOI 6
SKIP_EOI?
>
> /* The last 8 bits are used to indicate how to interpret the flags field
> * in pvclock structure. If no bits are set, all flags are ignored.
> @@ -37,6 +38,7 @@
> #define MSR_KVM_SYSTEM_TIME_NEW 0x4b564d01
> #define MSR_KVM_ASYNC_PF_EN 0x4b564d02
> #define MSR_KVM_STEAL_TIME 0x4b564d03
> +#define MSR_KVM_EOI_EN 0x4b564d04
>
> struct kvm_steal_time {
> __u64 steal;
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index eba8345..bda4877 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -408,6 +408,7 @@ static int do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
> (1 << KVM_FEATURE_NOP_IO_DELAY) |
> (1 << KVM_FEATURE_CLOCKSOURCE2) |
> (1 << KVM_FEATURE_ASYNC_PF) |
> + (1 << KVM_FEATURE_EOI) |
> (1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT);
>
> if (sched_info_on())
> diff --git a/arch/x86/kvm/irq.c b/arch/x86/kvm/irq.c
> index 7e06ba1..07bdfab 100644
> --- a/arch/x86/kvm/irq.c
> +++ b/arch/x86/kvm/irq.c
> @@ -48,7 +48,7 @@ int kvm_cpu_has_interrupt(struct kvm_vcpu *v)
> if (!irqchip_in_kernel(v->kvm))
> return v->arch.interrupt.pending;
>
> - if (kvm_apic_has_interrupt(v) == -1) { /* LAPIC */
> + if (kvm_apic_has_interrupt(v) < 0) { /* LAPIC */
> if (kvm_apic_accept_pic_intr(v)) {
> s = pic_irqchip(v->kvm); /* PIC */
> return s->output;
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 93c1574..c7e6ffb 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -270,6 +270,54 @@ int kvm_apic_set_irq(struct kvm_vcpu *vcpu, struct kvm_lapic_irq *irq)
> irq->level, irq->trig_mode);
> }
>
> +static int eoi_put_user(struct kvm_vcpu *vcpu, u8 val)
> +{
> +
> + return kvm_write_guest_cached(vcpu->kvm, &vcpu->arch.eoi.data, &val,
> + sizeof(val));
> +}
> +
> +static int eoi_get_user(struct kvm_vcpu *vcpu, u8 *val)
> +{
> +
> + return kvm_read_guest_cached(vcpu->kvm, &vcpu->arch.eoi.data, val,
> + sizeof(*val));
> +}
> +
> +static inline bool eoi_enabled(struct kvm_vcpu *vcpu)
> +{
> + return vcpu->arch.eoi.msr_val & KVM_MSR_ENABLED;
> +}
Please find a more descriptive name, such as pv_eoi_* (or skip_eoi,
or...).
> +
> +static bool eoi_get_pending(struct kvm_vcpu *vcpu)
> +{
> + u8 val;
> + if (eoi_get_user(vcpu, &val) < 0)
> + apic_debug("Can't read EOI MSR value: 0x%llx\n",
> + (unsigned long long)vcpi->arch.eoi.msr_val);
> + return val & 0x1;
> +}
> +
> +static void eoi_set_pending(struct kvm_vcpu *vcpu)
> +{
> + if (eoi_put_user(vcpu, 0x1) < 0) {
> + apic_debug("Can't set EOI MSR value: 0x%llx\n",
> + (unsigned long long)vcpi->arch.eoi.msr_val);
> + return;
> + }
> + __set_bit(KVM_APIC_EOI_PENDING, &vcpu->arch.apic_attention);
> +}
> +
> +static void eoi_clr_pending(struct kvm_vcpu *vcpu)
> +{
> + if (eoi_put_user(vcpu, 0x0) < 0) {
> + apic_debug("Can't clear EOI MSR value: 0x%llx\n",
> + (unsigned long long)vcpi->arch.eoi.msr_val);
> + return;
> + }
> + __clear_bit(KVM_APIC_EOI_PENDING, &vcpu->arch.apic_attention);
> +}
> +
> static inline int apic_find_highest_isr(struct kvm_lapic *apic)
> {
> int result;
> @@ -482,16 +530,21 @@ int kvm_apic_compare_prio(struct kvm_vcpu *vcpu1, struct kvm_vcpu *vcpu2)
> return vcpu1->arch.apic_arb_prio - vcpu2->arch.apic_arb_prio;
> }
>
> -static void apic_set_eoi(struct kvm_lapic *apic)
> +static int apic_set_eoi(struct kvm_lapic *apic)
> {
> int vector = apic_find_highest_isr(apic);
> +
> + trace_kvm_eoi(apic, vector);
> +
> /*
> * Not every write EOI will has corresponding ISR,
> * one example is when Kernel check timer on setup_IO_APIC
> */
> if (vector == -1)
> - return;
> + return vector;
>
> + if (eoi_enabled(apic->vcpu))
> + eoi_clr_pending(apic->vcpu);
Why is this here again? If you got here, the bit should be cleared
already?
> apic_clear_vector(vector, apic->regs + APIC_ISR);
> apic_update_ppr(apic);
>
> @@ -505,6 +558,7 @@ static void apic_set_eoi(struct kvm_lapic *apic)
> kvm_ioapic_update_eoi(apic->vcpu->kvm, vector, trigger_mode);
> }
> kvm_make_request(KVM_REQ_EVENT, apic->vcpu);
> + return vector;
> }
>
> static void apic_send_ipi(struct kvm_lapic *apic)
> @@ -1085,6 +1139,7 @@ void kvm_lapic_reset(struct kvm_vcpu *vcpu)
> atomic_set(&apic->lapic_timer.pending, 0);
> if (kvm_vcpu_is_bsp(vcpu))
> vcpu->arch.apic_base |= MSR_IA32_APICBASE_BSP;
> + vcpu->arch.eoi.msr_val = 0;
> apic_update_ppr(apic);
>
> vcpu->arch.apic_arb_prio = 0;
> @@ -1211,9 +1266,10 @@ int kvm_apic_has_interrupt(struct kvm_vcpu *vcpu)
>
> apic_update_ppr(apic);
> highest_irr = apic_find_highest_irr(apic);
> - if ((highest_irr == -1) ||
> - ((highest_irr & 0xF0) <= apic_get_reg(apic, APIC_PROCPRI)))
> + if (highest_irr == -1)
> return -1;
> + if (((highest_irr & 0xF0) <= apic_get_reg(apic, APIC_PROCPRI)))
> + return -2;
> return highest_irr;
> }
>
> @@ -1245,9 +1301,20 @@ int kvm_get_apic_interrupt(struct kvm_vcpu *vcpu)
> int vector = kvm_apic_has_interrupt(vcpu);
> struct kvm_lapic *apic = vcpu->arch.apic;
>
> - if (vector == -1)
> + /* Detect interrupt nesting and disable EOI optimization */
> + if (eoi_enabled(vcpu) && vector == -2)
> + eoi_clr_pending(vcpu);
> +
> + if (vector < 0)
> return -1;
>
> + if (eoi_enabled(vcpu)) {
> + if (kvm_ioapic_handles_vector(vcpu->kvm, vector))
> + eoi_clr_pending(vcpu);
> + else
> + eoi_set_pending(vcpu);
> + }
> +
> apic_set_vector(vector, apic->regs + APIC_ISR);
> apic_update_ppr(apic);
> apic_clear_irr(vector, apic);
> @@ -1262,6 +1329,14 @@ void kvm_apic_post_state_restore(struct kvm_vcpu *vcpu)
> MSR_IA32_APICBASE_BASE;
> kvm_apic_set_version(vcpu);
>
> + if (eoi_enabled(apic->vcpu)) {
> + if (eoi_get_pending(apic->vcpu))
> + __set_bit(KVM_APIC_EOI_PENDING,
> + &vcpu->arch.apic_attention);
> + else
> + __clear_bit(KVM_APIC_EOI_PENDING,
> + &vcpu->arch.apic_attention);
> + }
Why is this necessary? kvm_apic_post_state_restore cannot change the
per cpu in memory value.
> apic_update_ppr(apic);
> hrtimer_cancel(&apic->lapic_timer.timer);
> update_divide_count(apic);
> @@ -1283,11 +1358,25 @@ void __kvm_migrate_apic_timer(struct kvm_vcpu *vcpu)
> hrtimer_start_expires(timer, HRTIMER_MODE_ABS);
> }
>
> +static void apic_update_eoi(struct kvm_lapic *apic)
> +{
> + int vector;
> + BUG_ON(!eoi_enabled(apic->vcpu));
> + if (eoi_get_pending(apic->vcpu))
> + return;
> + __clear_bit(KVM_APIC_EOI_PENDING, &apic->vcpu->arch.apic_attention);
> + vector = apic_set_eoi(apic);
> + trace_kvm_pv_eoi(apic, vector);
> +}
KVM_APIC_EOI_PENDING appears to be a shadow of the pervcpu value,
to speed up processing. If it is, please make that clear.
> void kvm_lapic_sync_from_vapic(struct kvm_vcpu *vcpu)
> {
> u32 data;
> void *vapic;
>
> + if (test_bit(KVM_APIC_EOI_PENDING, &vcpu->arch.apic_attention))
> + apic_update_eoi(vcpu->arch.apic);
> +
> if (!test_bit(KVM_APIC_CHECK_VAPIC, &vcpu->arch.apic_attention))
> return;
>
> @@ -1394,3 +1483,14 @@ int kvm_hv_vapic_msr_read(struct kvm_vcpu *vcpu, u32 reg, u64 *data)
>
> return 0;
> }
> +
> +int kvm_pv_enable_apic_eoi(struct kvm_vcpu *vcpu, u64 data)
> +{
> + u64 addr = data & ~KVM_MSR_ENABLED;
> + if (eoi_enabled(vcpu))
> + eoi_clr_pending(vcpu);
> + vcpu->arch.eoi.msr_val = data;
> + if (!eoi_enabled(vcpu))
> + return 0;
> + return kvm_gfn_to_hva_cache_init(vcpu->kvm, &vcpu->arch.eoi.data, addr);
> +}
> diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
> index 6f4ce25..042dace 100644
> --- a/arch/x86/kvm/lapic.h
> +++ b/arch/x86/kvm/lapic.h
> @@ -60,4 +60,6 @@ static inline bool kvm_hv_vapic_assist_page_enabled(struct kvm_vcpu *vcpu)
> {
> return vcpu->arch.hv_vapic & HV_X64_MSR_APIC_ASSIST_PAGE_ENABLE;
> }
> +
> +int kvm_pv_enable_apic_eoi(struct kvm_vcpu *vcpu, u64 data);
> #endif
> diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h
> index 911d264..851914e 100644
> --- a/arch/x86/kvm/trace.h
> +++ b/arch/x86/kvm/trace.h
> @@ -517,6 +517,40 @@ TRACE_EVENT(kvm_apic_accept_irq,
> __entry->coalesced ? " (coalesced)" : "")
> );
>
> +TRACE_EVENT(kvm_eoi,
> + TP_PROTO(struct kvm_lapic *apic, int vector),
> + TP_ARGS(apic, vector),
> +
> + TP_STRUCT__entry(
> + __field( __u32, apicid )
> + __field( int, vector )
> + ),
> +
> + TP_fast_assign(
> + __entry->apicid = apic->vcpu->vcpu_id;
> + __entry->vector = vector;
> + ),
> +
> + TP_printk("apicid %x vector %d", __entry->apicid, __entry->vector)
> +);
> +
> +TRACE_EVENT(kvm_pv_eoi,
> + TP_PROTO(struct kvm_lapic *apic, int vector),
> + TP_ARGS(apic, vector),
> +
> + TP_STRUCT__entry(
> + __field( __u32, apicid )
> + __field( int, vector )
> + ),
> +
> + TP_fast_assign(
> + __entry->apicid = apic->vcpu->vcpu_id;
> + __entry->vector = vector;
> + ),
> +
> + TP_printk("apicid %x vector %d", __entry->apicid, __entry->vector)
> +);
> +
> /*
> * Tracepoint for nested VMRUN
> */
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 185a2b8..bfcd97d 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -795,6 +795,7 @@ static u32 msrs_to_save[] = {
> MSR_KVM_SYSTEM_TIME_NEW, MSR_KVM_WALL_CLOCK_NEW,
> HV_X64_MSR_GUEST_OS_ID, HV_X64_MSR_HYPERCALL,
> HV_X64_MSR_APIC_ASSIST_PAGE, MSR_KVM_ASYNC_PF_EN, MSR_KVM_STEAL_TIME,
> + MSR_KVM_EOI_EN,
> MSR_IA32_SYSENTER_CS, MSR_IA32_SYSENTER_ESP, MSR_IA32_SYSENTER_EIP,
> MSR_STAR,
> #ifdef CONFIG_X86_64
> @@ -1653,6 +1654,10 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
> kvm_make_request(KVM_REQ_STEAL_UPDATE, vcpu);
>
> break;
> + case MSR_KVM_EOI_EN:
> + if (kvm_pv_enable_apic_eoi(vcpu, data))
> + return 1;
> + break;
>
> case MSR_IA32_MCG_CTL:
> case MSR_IA32_MCG_STATUS:
> @@ -5370,7 +5375,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> if (unlikely(vcpu->arch.tsc_always_catchup))
> kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
>
> - kvm_lapic_sync_from_vapic(vcpu);
> + if (unlikely(vcpu->arch.apic_attention))
> + kvm_lapic_sync_from_vapic(vcpu);
This apic_attention check is unrelated, please have in a separate patch.
Also please document that this is only possible because of interrupt window
exiting.
The Hyper-V spec, does it provide similar interface ? It mentions
that "Most EOI intercepts can be eliminated and done lazily if the guest
OS leaves a marker when it performs an EOI".
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